Newbie - help with oddball setup

JR2980
JR2980 Registered Users Posts: 14 ✭
in Off Grid Solar & Battery Systems #1
Hi everyone - new guy here, and I need some help! (at least thats what my wife constantly tells me :D )

I'm not really sure if this is the right section for this question, so mods, please feel free to move it if necessary.

My question relates to using a genset to recharge a battery bank. I will not be using the genset to recharge all the time, but want the option when needed.

The PV side of the system is really irrelevant to this discussion, so I wont get into it at all.

Say I have a battery bank with 4 100ah 12v batteries wired in parallel series so that I have a 200ah 24v battery bank. If I use no more than 60% of the total capacity, then the most I'll ever discharge will be 120ah.


Now to the oddball part.....

I recently acquired a diesel DC genset capable of delivering 71+/- amps continuously at a nominal 28v (2kw). The genset is regulated to maintain a constant voltage, and the voltage is manually adjustable in a range from 26.6v to 32.2v. If it helps, the genset is a MEP-501a, and the manual is available here-> http://www.deweyelectronics.com/assets/pdfs/misc/2kW-Military-Tactical-Generator-Sets-Technical-Manual.pdf

I want to use the genset to help charge the battery bank quickly when needed, and I want to make sure that I'm not going to damage the genset or the battery bank.

Now, the math I did was - assuming I need to recharge the battery bank that sits at 40%, I should be able to push a minimum of 60amps continuous from the genset, so using those numbers with this formula: capacity/hours = amps, 120ah / 2Hours = 60 amps..... I should be able to recharge the battery bank that has been discharged to 40%, in 2 hours. If I'm wrong here, please let me know.


My next question is, do I need a charge controller (I'm guessing yes) between the genset and the battery bank. Here's where I get a little lost. I've been looking at the Xantrex C60 - I even spoke to someone at Xantrex, though they were less than helpful.

Here's what I think..... I think I can hook the C60 up between the genset and the battery bank, and set the generator output voltage to 32v. The C60 will take that 32v and step it down to whatever is necessary to charge the batteries depending on their state. What I haven't been able to wrap my head around is the current, and this comes back more to my ignorance on power generation. The genset runs at 28v and can deliver up to a nominal 71amps (2K watts), but it it will only deliver as much current as the load "asks" for right? I'm afraid that if I hook the battery bank up directly to the genset, a deeply discharged battery could easily exceed the current limits of the genset and overload it - hence the charge controller - if I understand correctly, the charge controller will only supply up to 60 amps, so it could never "ask" for more than that from the generator (taking into account losses due inefficiencies it could be slightly higher than 60amps but should be well within the tolerances of the genset....I think).

Maybe this is a stupid question.....sorry if I didn't explain it very well. :blush:

Obviously, this is not going to be an everyday thing, but if a big storm rolls through, and we get overcast skies for 3-4 days straight, it sure would be nice to be able to recharge the battery bank since PV sure wouldn't keep up in that case.

I feel like I know enough to be dangerous, but not enough to be confident! :confused:



Thanks for any help!
JR
· Share on Twitter
«1

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Newbie - help with oddball setup

    Welcome to the forum JR.

    Well "oddball set-up" is my middle name. My mother had a strange sense of humour. :D

    Let's simplify this.

    You've got a battery bank of 200 Amp hours @ 24 Volts. You've got a DC genset which put out 26 to 32 Volts at up to 71 Amps.

    What you haven't got is any way of regulating that output to charge the battery. The idea of installing a PWM type controller in between is good, but not without a couple of issues.

    First of these is Voltage. You will need to crank it up, and then possibly down again once you get the system working in order to find that spot that can deliver the 28.8 Volts for Absorb. This may take more fiddling than you think due to the second issue.

    Second issue is current. You only need 40 Amps maximum and that not sustain. 20 Amps would be better for 200 Amp hours, and a peak of 30 Amps is a good idea. Problem: PWM type controllers usually don't limit current. Put the C60 in and when the batteries are low the gen will try to push 70 Amps through it and the controller will fry. So we need to limit current on the gen's output.

    Using an MPPT type controller might be suggested, but it isn't going to 'like' the impure DC of the gen and will probably go haywire as a result.

    I'm not certain but I think Morningstar's TriStar PWM can be programmed to limit output current using a computer connection and their software. If someone here has the info on that it would be appreciated.

    The other choice is to add a load on the gen output to take up some of its power before the charge controller. It would need to be something that would draw 40 Amps so that a maximum of 30 Amps would be available for charging. Putting this additional load on the gen will make it run more efficiently too, providing the load is actually doing something practical (such as heating a tank of water). You're looking at roughly 1200 Watts.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Newbie - help with oddball setup
    JR2980 wrote: »
    I recently acquired a diesel DC genset capable of delivering 71+/- amps continuously at a nominal 28v (2kw). The genset is regulated to maintain a constant voltage, and the voltage is manually adjustable in a range from 26.6v to 32.2v. If it helps, the genset is a MEP-501a, and the manual is available here-> http://www.deweyelectronics.com/assets/pdfs/misc/2kW-Military-Tactical-Generator-Sets-Technical-Manual.pdf

    I want to use the genset to help charge the battery bank quickly when needed, and I want to make sure that I'm not going to damage the genset or the battery bank.

    Now, the math I did was - assuming I need to recharge the battery bank that sits at 40%, I should be able to push a minimum of 60amps continuous from the genset, so using those numbers with this formula: capacity/hours = amps, 120ah / 2Hours = 60 amps..... I should be able to recharge the battery bank that has been discharged to 40%, in 2 hours. If I'm wrong here, please let me know.

    More or less, a Lead Acid battery bank can take "large amounts of charging current" up to around 80% state of charge (20-25% or more?). Once the battery bank is over >~80% state of charge, the battery will be at ~14.75 volts or so, and the current will be reduced by the battery charger/controller. Basically:

    0-80% SOC, the charging course is "current limited". Solar RE companies call this "Bulk" charging
    80-90%+ is "voltage limited" charging. Also called "Absorb" charing
    90-100% is a lower voltage charging (maintaining charge). Called "Float" charging

    So, the time for battery charging... The Bulk phase is pretty much the math you state... AH / Amp charging = Hours charging time.

    However, once you hit the ~80-85% SOC, the Absorb phase is basically time. For a "shallow" discharged battery, this is around 2 hours minimum. For a deep cycled battery, you are probably looking at a 4-6 hour charging cycle.

    And this is where gensets become an issue. They are pretty fuel efficient when operated at 50% to 100% of rated output, and when you drop below 25% of rated output, gensets can be very fuel inefficient (and diesel gensets can "wet stack"/"coke up"/glaze cylinder walls).

    We generally suggest using a genset at higher current output for charging up to ~80% SOC (do this early morning), and let the solar array finish the Absorb cycle.
    My next question is, do I need a charge controller (I'm guessing yes) between the genset and the battery bank. Here's where I get a little lost. I've been looking at the Xantrex C60 - I even spoke to someone at Xantrex, though they were less than helpful.

    Here's what I think..... I think I can hook the C60 up between the genset and the battery bank, and set the generator output voltage to 32v. The C60 will take that 32v and step it down to whatever is necessary to charge the batteries depending on their state. What I haven't been able to wrap my head around is the current, and this comes back more to my ignorance on power generation. The genset runs at 28v and can deliver up to a nominal 71amps (2K watts), but it it will only deliver as much current as the load "asks" for right? I'm afraid that if I hook the battery bank up directly to the genset, a deeply discharged battery could easily exceed the current limits of the genset and overload it - hence the charge controller - if I understand correctly, the charge controller will only supply up to 60 amps, so it could never "ask" for more than that from the generator (taking into account losses due inefficiencies it could be slightly higher than 60amps but should be well within the tolerances of the genset....I think).

    A C60 is a PWM (pulse width modulation) type of charge controller... Basically it is an "on/off" switch that cycles every few seconds to hundreds of times a second to give you the "average voltage" you want.

    Re-right this part--Missed this was a 24 volt battery bank.

    A C60 could work OK... But it is a bit small for a 70 amp genset. Also, you would have to crank the genset voltage up a couple volts to allow the C60 to regulate. You need to look at the genset's regulation/electrical performance to see if a cycling PWM controller would work with it or not

    I am not sure a DC generator+PWM type charge controller will be a good match (inductive genset could cause high voltage surges everytime the C60 cycles off).

    Just adjusting the genset to the charging voltage would be a better solution and avoid the C60 completely.
    Maybe this is a stupid question.....sorry if I didn't explain it very well. :blush:

    Obviously, this is not going to be an everyday thing, but if a big storm rolls through, and we get overcast skies for 3-4 days straight, it sure would be nice to be able to recharge the battery bank since PV sure wouldn't keep up in that case.

    I feel like I know enough to be dangerous, but not enough to be confident! :confused:

    A Honda eu2000i (or similar Yamaha inverter generator) 1,600 watt genset + couple hundred dollar AC battery charger would probably more fuel/cost efficient over time--Plus it gives you a small/fuel efficient backup genset to (when your inverter eventually fails).

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #4
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    Welcome to the forum JR.

    Well "oddball set-up" is my middle name. My mother had a strange sense of humour. :D

    Thanks for the input!

    Cariboocoot wrote: »
    First of these is Voltage. You will need to crank it up, and then possibly down again once you get the system working in order to find that spot that can deliver the 28.8 Volts for Absorb. This may take more fiddling than you think due to the second issue.

    This is why I was looking at the C60 as it can regulate the voltage - I can set the genset to supply 32v, and let the C60 the voltage down to whatever level it needs to be at for charging.

    Cariboocoot wrote: »
    Second issue is current. You only need 40 Amps maximum and that not sustain. 20 Amps would be better for 200 Amp hours, and a peak of 30 Amps is a good idea. Problem: PWM type controllers usually don't limit current. Put the C60 in and when the batteries are low the gen will try to push 70 Amps through it and the controller will fry. So we need to limit current on the gen's output.

    This is where I get lost - I understand constantly delivering 28v, but I don't understand the current delivery. The genset is rated at 2kw, so at 28v that would come out to just over 71amps - but does that mean that the genset is pushing out that 71amps all the time? I didn't think so since if that were the case it would only be able to power something that needed to use the full 71amp - if for instance I connect a 28v 60w lamp, it should only draw 2.1amps or so correct? What then happens to the other 68+/- amps at the genset? Shouldnt the same logic apply to a charge controller that is only rated to supply up to 60 amps to the battery bank...if it only supplies 60 amps, isnt that the most it would ever draw from the genset?




    I'm sure that I'm missing something, and probably something simple!
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #5
    Re: Newbie - help with oddball setup

    Thanks for the input!

    BB. wrote: »

    A C60 could work OK... But it is a bit small for a 70 amp genset. Also, you would have to crank the genset voltage up a couple volts to allow the C60 to regulate. You need to look at the genset's regulation/electrical performance to see if a cycling PWM controller would work with it or not

    I am not sure a DC generator+PWM type charge controller will be a good match (inductive genset could cause high voltage surges everytime the C60 cycles off).

    I wouldnt even begin to know what to look at as far as the genset specs to determine is the PWM controller would work or not, or if the genset is inductive or not


    BB. wrote: »
    Just adjusting the genset to the charging voltage would be a better solution and avoid the C60 completely.

    I thought about that and in a pinch I could do that, but I'd like to have a way to let a charge controller manage all of that for me - just to take me and my ignorance out of the loop! :D


    BB. wrote: »
    A Honda eu2000i (or similar Yamaha inverter generator) 1,600 watt genset + couple hundred dollar AC battery charger would probably more fuel/cost efficient over time--Plus it gives you a small/fuel efficient backup genset to (when your inverter eventually fails).

    Your thoughts?

    -Bill


    I've got a small/cheap/Chinese 24v inverter that I plan to test - I'm going to hook it up directly to the genset and see what happens! :)

    I really want to stay with the diesel genset - its small and easy to move around (under 150lbs) - plus, I have a couple of larger diesel gensets (5kw) and all of my vehicles are diesel (truck/tractor/atv), and I have bulk diesel storage available, so I'm planning to get away completely from gasoline. This DC genset only cost $300 and sips fuel (.3gph at 75% load), so if I can make it work, that's just a bonus. I figured that I could charge the battery bank much quicker with this than trying to do it via an AC generator and running a battery charger off of it. A charger running off of an AC source will take much longer to charge the battery bank wouldn't it? I was hoping to be able to run this generator for a couple of hours tops just to push a charge to the battery bank when needed.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Newbie - help with oddball setup

    Current from a constant Voltage power source is subject to Ohm's law: I = V/R. V is Voltage, R is resistance in Ohms, I is current.

    So you are correct that 2kW @ 28 Volts is (2000 / 28 ) 71 Amps. But the actual current will depend on the resistance of the load. With a battery this varies as a function of its state of charge: low charge = low resistance = high current. It's not easily predictable because you can't measure the battery's resistance with an Ohmmeter. The problem is that it may demand more current than is good for it. Hence we try to keep the maximum available current from going above that point where it will cook the battery.

    Moreover, this will probably be on an active system which means loads will draw some of that current potential. But you can't rely on them to be steady or predictable. Again we come back to limiting the maximum to protect the battery.

    Cheapest, easiest way would be to put a 30 Amp DC breaker on the gen's output to the charge controller. Should the current go above that for any reason the breaker will trip. Might get to be a pain with it tripping every time the refrigerator comes on. If you limit the current in another manner then the loads will be accommodated up to the maximum allowed from the gen and any difference will be made up by the batteries discharging. Load off, full charging resumes. But that relies on putting that 1200 Watt load on the gen as I mentioned before.

    Another method: use two PWM controllers as diversion load controllers. Gen connects directly to the battery, Voltage is regulated by the controllers shunting excess power to diversion load. In that case you need the controllers to handle more than the gen can put out - as in two 60 Amp controllers - and the diversion load must be able to take the full power of 2kW. I would not recommend this method as it has too many things that may go wrong.

    On the whole I think the constant load on the gen output to limit the power available for charging is the easiest and safest method. Ideally this would have ganged DC breakers on it so if the load failed from over-current it would disconnect power to the controller as well. Even so if the connected opened full power would be available to the controller and it might be subjected to 70 Amps. In which case having a 40 Amp DC breaker on the controller input would be a good idea.

    No matter what you do there's always some way for something to go wrong. :roll:
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Newbie - help with oddball setup
    JR2980 wrote: »
    Thanks for the input!

    I've got a small/cheap/Chinese 24v inverter that I plan to test - I'm going to hook it up directly to the genset and see what happens! :)

    Don't do this. The gen output is probably not regulated well enough to keep the Voltage steady within the inverter's range as loads vary. Most likely the inverter will fry.
    I really want to stay with the diesel genset - its small and easy to move around (under 150lbs) - plus, I have a couple of larger diesel gensets (5kw) and all of my vehicles are diesel (truck/tractor/atv), and I have bulk diesel storage available, so I'm planning to get away completely from gasoline. This DC genset only cost $300 and sips fuel (.3gph at 75% load), so if I can make it work, that's just a bonus. I figured that I could charge the battery bank much quicker with this than trying to do it via an AC generator and running a battery charger off of it. A charger running off of an AC source will take much longer to charge the battery bank wouldn't it? I was hoping to be able to run this generator for a couple of hours tops just to push a charge to the battery bank when needed.

    I think it can be made to work if the proper precautions are taken.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Newbie - help with oddball setup
    JR2980 wrote: »
    I wouldnt even begin to know what to look at as far as the genset specs to determine is the PWM controller would work or not, or if the genset is inductive or not

    In general electric motors and generators have a fair amount of inductance. Switching inductive loads with current flow creates a inductive kick back that can arc over the contacts (or FETs) unless a snubbing capacitor or diode is used (remember the condensor used in point type ignition systems).

    Using a PWM controller as the final regulator for a DC generator--Not my first choice.
    I thought about that and in a pinch I could do that, but I'd like to have a way to let a charge controller manage all of that for me - just to take me and my ignorance out of the loop!

    No--Does not work well that way. Even if you get everything dialed in/automated the way you want it to work--It will eventually fail somehow/sometime. Highly automated systems seem to find more ways to fail than we can figure out how to fail-safe/monitor them. :cry:

    So, my suggestion is to start out simple--Get your system up and running. Then look at automating specific tasks that make sense.

    In general, your most efficient fuel usage will be to start the genset around 50% state of charge and run it to around 80% state of charge, then shut it down. You want the genset running at ~50-80% of rated output current (if commercial/industrial design, you should be able to run near 100% continuous output).

    It turns out there is another way to "manage" Lead Acid battery banks. We think of charging them to 100% at the end of every day (or after a couple of days of no-sun). First, you really only want to charge to >90% stage of charge. That last 10% takes a lot of extra energy (50% or less efficient charging/chemistry conversion), uses a lot of extra water (gassing), and is sort of hard on the battery bank (batteries heat up, erosion of plates, oxygen corrosion of the positive grid in the plates, etc.).

    An alternative is to cycle the battery from 80-50-80% daily--And recharge back >90% once every ~7-10 days (one vendor says once every ~4 weeks). This is a much more efficient charging regime and pretty good for overall battery life. As long as you are cycling daily, you should not have issues with sulfation (batteries standing without charge cycling, or at less than ~75% state of charge will convert the soft/fluffy lead sulfate to hard lead sulfate crystals--permanently lessening the capacity of the battery bank).

    So--If you notice, we talk about State of Charge when looking at battery "state of charge". We don't talk about battery voltage--So "smart" regulation based on voltage becomes quite difficult. Ideally, you want to monitor current flow and time (amp*hours) estimate the state of charge of the battery bank.
    I've got a small/cheap/Chinese 24v inverter that I plan to test - I'm going to hook it up directly to the genset and see what happens! :)

    AC inverters are (generally) designed to operate from a very low "impedance" source--Like a large battery bank. An inverter can draw upwards of 2x of rated current during motor starting surges (pumps, etc.). As long as your running/surge current do not exceed the generator rated output current--It may work.

    There is an issue that AC inverters are "constant power" devices. You may see surging/DC bus voltage stability issues when directly driving an AC inverter... A constant power device (P=I*V)--When the DC voltage rises, the current falls, which causes current to fall more--And the opposite, when the current increases, causing voltage to fall, the current drawn by the inverter increases more, and the voltage falls more--As you can see, this can become a stability issue for the generator regulator and the AC inverter feedback design.

    Another issue is that AC inverters do not draw a "constant" DC current, they actually draw current at 120 Hz sine wave type current profile (specifically a "sine squared" wave form). You may need some good sized capacitors at the input of the AC inverter to stabilize the DC voltage from the genset.

    I guess I am saying, don't be too surprised if your DC genset+AC inverter does not perform as expected and at rated output... There are a lot of potential issues that can byte you in the behind.
    I really want to stay with the diesel genset - its small and easy to move around (under 150lbs) - plus, I have a couple of larger diesel gensets (5kw) and all of my vehicles are diesel (truck/tractor/atv), and I have bulk diesel storage available, so I'm planning to get away completely from gasoline. This DC genset only cost $300 and sips fuel (.3gph at 75% load), so if I can make it work, that's just a bonus. I figured that I could charge the battery bank much quicker with this than trying to do it via an AC generator and running a battery charger off of it. A charger running off of an AC source will take much longer to charge the battery bank wouldn't it? I was hoping to be able to run this generator for a couple of hours tops just to push a charge to the battery bank when needed.

    For you--Diesel is obviously the best solution. And if you can manually (or automate) the running of your diesel genset at 50%-80% State of charge, you will be quite happy.

    Others do that here and are very happy with their systems. Obviously, adding a warm up/cool down cycle to the genest is going to help with genset life/smoke production too.

    Your "difference" is you want to do this with a DC output genset. There are AC inverter systems that already automate generator operations following this profile--It is just they do it with 120/240 VAC power, not DC. So that makes it a bit more difficult for your setup.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #9
    Re: Newbie - help with oddball setup

    What about just increasing the capacity of the bank? Either bigger Ah to suit genset, or go AGM which can take more amps...


    BB. wrote: »
    In general electric motors and generators have a fair amount of inductance. Switching inductive loads with current flow creates a inductive kick back that can arc over the contacts (or FETs) unless a snubbing capacitor or diode is used (remember the condensor used in point type ignition systems).

    Using a PWM controller as the final regulator for a DC generator--Not my first choice.



    No--Does not work well that way. Even if you get everything dialed in/automated the way you want it to work--It will eventually fail somehow/sometime. Highly automated systems seem to find more ways to fail than we can figure out how to fail-safe/monitor them. :cry:

    So, my suggestion is to start out simple--Get your system up and running. Then look at automating specific tasks that make sense.

    In general, your most efficient fuel usage will be to start the genset around 50% state of charge and run it to around 80% state of charge, then shut it down. You want the genset running at ~50-80% of rated output current (if commercial/industrial design, you should be able to run near 100% continuous output).

    It turns out there is another way to "manage" Lead Acid battery banks. We think of charging them to 100% at the end of every day (or after a couple of days of no-sun). First, you really only want to charge to >90% stage of charge. That last 10% takes a lot of extra energy (50% or less efficient charging/chemistry conversion), uses a lot of extra water (gassing), and is sort of hard on the battery bank (batteries heat up, erosion of plates, oxygen corrosion of the positive grid in the plates, etc.).

    An alternative is to cycle the battery from 80-50-80% daily--And recharge back >90% once every ~7-10 days (one vendor says once every ~4 weeks). This is a much more efficient charging regime and pretty good for overall battery life. As long as you are cycling daily, you should not have issues with sulfation (batteries standing without charge cycling, or at less than ~75% state of charge will convert the soft/fluffy lead sulfate to hard lead sulfate crystals--permanently lessening the capacity of the battery bank).

    So--If you notice, we talk about State of Charge when looking at battery "state of charge". We don't talk about battery voltage--So "smart" regulation based on voltage becomes quite difficult. Ideally, you want to monitor current flow and time (amp*hours) estimate the state of charge of the battery bank.



    AC inverters are (generally) designed to operate from a very low "impedance" source--Like a large battery bank. An inverter can draw upwards of 2x of rated current during motor starting surges (pumps, etc.). As long as your running/surge current do not exceed the generator rated output current--It may work.

    There is an issue that AC inverters are "constant power" devices. You may see surging/DC bus voltage stability issues when directly driving an AC inverter... A constant power device (P=I*V)--When the DC voltage rises, the current falls, which causes current to fall more--And the opposite, when the current increases, causing voltage to fall, the current drawn by the inverter increases more, and the voltage falls more--As you can see, this can become a stability issue for the generator regulator and the AC inverter feedback design.

    Another issue is that AC inverters do not draw a "constant" DC current, they actually draw current at 120 Hz sine wave type current profile (specifically a "sine squared" wave form). You may need some good sized capacitors at the input of the AC inverter to stabilize the DC voltage from the genset.

    I guess I am saying, don't be too surprised if your DC genset+AC inverter does not perform as expected and at rated output... There are a lot of potential issues that can byte you in the behind.



    For you--Diesel is obviously the best solution. And if you can manually (or automate) the running of your diesel genset at 50%-80% State of charge, you will be quite happy.

    Others do that here and are very happy with their systems. Obviously, adding a warm up/cool down cycle to the genest is going to help with genset life/smoke production too.

    Your "difference" is you want to do this with a DC output genset. There are AC inverter systems that already automate generator operations following this profile--It is just they do it with 120/240 VAC power, not DC. So that makes it a bit more difficult for your setup.

    -Bill
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Newbie - help with oddball setup

    Yes, AGM's would be good alternative... I tend to "forget them" as they generally cost about 2x that of flooded cell, and AGM may have a few years less life vs flooded cell batteries (that are well cared for).

    The smaller battery bank could be done with with AGM's driving the microwave.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #11
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    I think it can be made to work if the proper precautions are taken.


    I sure hope so!
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #12
    Re: Newbie - help with oddball setup

    Thanks to everyone that has replied so far - I really appreciate the help!



    The generator has a CB in place already that (per the manufacturer) will trip after exceeding 72 amps (+/-), so I shouldn't be able to damage the genset, but if the breaker is tripping constantly, then its not charging and no good to me! It is voltage regulated so will do everything it can to maintain the voltage that I set it at, and will supply current up the CB limit.


    From what I gather so far, it seems that the charge controllers cannot regulate their input current, so I'm not seeing how using them as diversion controllers would work. If the load is determining how much current is delivered, then how does adding more load help to not exceed the genset limits? :confused:

    Let me see if I'm grasping this at all - I feel dumber now than when I started!!! :blush:.....


    If I hook up 10, 24v 200w lights directly to my genset, when off, there is no load, so no current. When a single light is turned on, it will use 8.3amps, so well within the genset capabilities. If I turn on 5 of those lights, it will draw 41.5amps, still well within genset limits. If I turn on all 10 of those lights, it will draw 83amps and exceed the genset limits, at which point the CB will trip.

    Seems pretty simple to me - static load - the light should never use more current than its rated for, so easy to size to the genset and determine how many I can run at any one time.


    Now, the dynamic load is where I cant seem to grasp (I'm going to use the C60, but I guess the same would apply for any charge controller)....


    If I hooked up the C60 to my genset, and don't connect a battery bank to the C60, there is no load, so no draw on the genset.

    If I then hook up a fully charged battery to the C60, again, no load, so no draw.

    If I connect a 10 amp load to the battery, now there is a 10 amp load that is well within the capabilities of both the C60 and the genset.

    If I were to connect a 70amp load, what would happen? Would the C60 only supply 60 amps since that's its max, or would it attempt to pass through the 70amps from the genset? At that point we're still within the capabilities of the genset, but exceeding the capabilities of the C60 (C60 probably fries).

    If I were to connect a 200ah battery discharged to, say, 40-50%, how much current would it potentially draw? Seems to me that it could easily exceed the capabilities of the genset nevermind overheating and damaging the batteries, but I dont know how to do the calculations.


    I guess what I need to know is how the load is presented to the genset......is the C60 only presenting its max load of 60amps to the genset, or is it presenting the actual 70amp load?

    If it will never present more than a 60 amp load to the generator, then I should have no problems, but if it will present whatever load is connected to it, then I will end up tripping the CB on the genset constantly when trying to charge a discharged battery bank.

    I cant wrap my head around how a diversion load will help here if the C60 just passes through whatever load is connected to it.....wouldn't that just trip the CB sooner?

    I thought that the purpose of the charge controller was to limit how much current was applied to the batteries during the different stages of charging in order to not damage the batteries - high current for bulk, then step that current down in stages to fully charge the battery. Seems like I may be wrong on that.




    Sorry for all the dumb questions - I just cant seem to grasp this. :confused::confused::confused:
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Newbie - help with oddball setup

    Sorry; it's an engineer thing. "Never give one answer when there are more available." :p

    We were talking about two different methods of regulation. One involving using charge controllers on a dump load and one involving using a static load to limit the current available to the charge controller on the batteries. The second method is the most sure-fire.

    The static load only needs to be large enough to limit the current available to the charge controller so that its maximum is not exceeded. 71 Amps - 60 Amps to the controller = 11 Amp static load. You'll actually want that a bit higher because you don't need the full 60 Amps for the batteries. That in combination with a breaker on the controller's input (in case something goes wrong) should make for a reasonable workable system.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #14
    Re: Newbie - help with oddball setup

    A C60 is a PWM type charge controller... Think of it as simply an "on/off" switch that cycles (some controllers switch on/off every few seconds, others will "cycle" 100s to 1,000s of times a second). If the switch is closed 50% of the cycle time, it is, on average, letting through 50% of the charging current. If it is closed 100% of the time--full charging current to battery... If it is closed 1% of the time, ~float charging batter.

    So, as far as the genset is concerned, a PWM controller cannot limit maximum current to the battery bank--Only modulate the "average charging current".

    With a generator--It is either rated to limit its own output current safely (more or less a current source)... I.e., 70 amps to battery bank if battery is at 21 volts (near dead) or 29 volts (near fully charged).

    If the DC generator is designed to operated live loads, and not charge a battery bank, it will output at ~27 volts output between 0 current and maximum current (all loads, plus surge current for starting loads, such as turning on a DC pump motor, starter motor APU--auxiliary power unit, etc.).

    Also, to be clear--Is your genset rated at 70 amps and you are tripping the breaker when charging your battery bank?

    Normally, a typical fuse/breaker is rated at 1.25 maximum continuous load:

    70 amps * 1.25 breaker/wiring deratings = 87.5 amps

    Generally fuses and breakers are designed to trip if operated at 100% of rated current (could take minutes to hours to open), and operate at 80% of rated current and never trip (note that fuses and many breakers are somewhat temperature sensitive--hot temperatures can cause trips at less than 80% rated current).

    Also, breakers do wear out/fail and can trip even at 80% or less of rated current.

    So--What is the actual genset rated output vs the breaker rating that you are using (and tripping?).

    Do you have a DC Current Clamp Meter (like this one or similar) to measure your actual current? Have you monitored the temperature of the (electrical) generator to see if it is over heating?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #15
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    Sorry; it's an engineer thing. "Never give one answer when there are more available." :p

    We were talking about two different methods of regulation. One involving using charge controllers on a dump load and one involving using a static load to limit the current available to the charge controller on the batteries. The second method is the most sure-fire.

    The static load only needs to be large enough to limit the current available to the charge controller so that its maximum is not exceeded. 71 Amps - 60 Amps to the controller = 11 Amp static load. You'll actually want that a bit higher because you don't need the full 60 Amps for the batteries. That in combination with a breaker on the controller's input (in case something goes wrong) should make for a reasonable workable system.


    But limiting the current available to the load needs to be handled by some type of regulator right? The only "regulator" right now for the current is the CB on the genset that trips if you exceed its capacity. If that CB is removed, the genset will push as much current as it can until it melts.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Newbie - help with oddball setup
    JR2980 wrote: »
    But limiting the current available to the load needs to be handled by some type of regulator right? The only "regulator" right now for the current is the CB on the genset that trips if you exceed its capacity. If that CB is removed, the genset will push as much current as it can until it melts.

    You do not remove the CB on the genset.

    The static load limits the current available to the charge controller. The charge controller will limit the current to the battery.

    Lets say the static load draws 21 Amps. Subtract that from the gen's 71 Amps maximum and you have 50 Amps maximum that can be used by the C60. This in combination with a 50 Amp circuit breaker on the C60's input will prevent the controller from being subjected to greater current than it can handle. The C60 will regulate the charging of the batteries.
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #17
    Re: Newbie - help with oddball setup
    BB. wrote: »
    A C60 is a PWM type charge controller... Think of it as simply an "on/off" switch that cycles (some controllers switch on/off every few seconds, others will "cycle" 100s to 1,000s of times a second). If the switch is closed 50% of the cycle time, it is, on average, letting through 50% of the charging current. If it is closed 100% of the time--full charging current to battery... If it is closed 1% of the time, ~float charging batter.

    So, as far as the genset is concerned, a PWM controller cannot limit maximum current to the battery bank--Only modulate the "average charging current".

    Ok - I think that answers my question about regulation. In a nutshell, the C60 (or any PWM charge controller) doesn't regulate the current.

    BB. wrote: »
    With a generator--It is either rated to limit its own output current safely (more or less a current source)... I.e., 70 amps to battery bank if battery is at 21 volts (near dead) or 29 volts (near fully charged).

    If the DC generator is designed to operated live loads, and not charge a battery bank, it will output at ~27 volts output between 0 current and maximum current (all loads, plus surge current for starting loads, such as turning on a DC pump motor, starter motor APU--auxiliary power unit, etc.).

    I guess the genset is designed to operate a load - it is voltage regulated (user selectable between 26.6v and 32.3v) and will supply up to 2KW (71amps). If a load of more than 71 amps is applied, there is a CB that will trip to protect the genset.

    So this wasn't designed to charge batteries - I'm still hoping that there would be a way to adapt it and use it that way.

    It would really suck to have to use an inverter to go to AC, then connect an AC-DC charger. I'm pretty sure that this would work - I don't know what the losses would be, but I have to think it would be pretty substantial, so I'd end up getting a percentage of the rated 70amps for charging, and wasting energy in the conversion process.


    BB. wrote: »
    Also, to be clear--Is your genset rated at 70 amps and you are tripping the breaker when charging your battery bank?

    I dont yet have it connected to the battery bank, and dont want to until I have an understanding of how/if its going to work and I know that I wont damage the genset or batteries (or anything else)

    BB. wrote: »
    Normally, a typical fuse/breaker is rated at 1.25 maximum continuous load:

    70 amps * 1.25 breaker/wiring deratings = 87.5 amps

    Generally fuses and breakers are designed to trip if operated at 100% of rated current (could take minutes to hours to open), and operate at 80% of rated current and never trip (note that fuses and many breakers are somewhat temperature sensitive--hot temperatures can cause trips at less than 80% rated current).

    Also, breakers do wear out/fail and can trip even at 80% or less of rated current.

    So--What is the actual genset rated output vs the breaker rating that you are using (and tripping?).

    I spoke to the manufacturer - they thought that what I was trying to do was "an interesting experiment" but for liability reasons, they wouldn't tell me anything other than the fact that there is a breaker that will trip if you exceed approximately 71 amps.

    The genset is rated at 2KW, so at 24v that would be about 71.4 amps


    BB. wrote: »
    Do you have a DC Current Clamp Meter (like this one or similar) to measure your actual current? Have you monitored the temperature of the (electrical) generator to see if it is over heating?

    -Bill

    I don't, but I am looking into getting one - this is the one that I've been considering..... http://www.amazon.com/gp/product/B005HOPRRK/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=A15QLX3KDITQKH

    I haven't monitored the genset to check its temp, but it is rated at 24v 2kw continuous, so as long as I don't draw more than 71 amps, I should be able to run it right up to that point.




    Thanks again!
    JR
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #18
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    You do not remove the CB on the genset.

    The static load limits the current available to the charge controller. The charge controller will limit the current to the battery.

    Lets say the static load draws 21 Amps. Subtract that from the gen's 71 Amps maximum and you have 50 Amps maximum that can be used by the C60. This in combination with a 50 Amp circuit breaker on the C60's input will prevent the controller from being subjected to greater current than it can handle. The C60 will regulate the charging of the batteries.



    But what happens if the batteries are deeply discharged - they would try to suck as many amps as they could, lets say 100amps, and since the C60 doesn't limit the input current, wouldn't the batteries then attempt to draw that much from the genset, and immediately trip the 50amp CB (or cook the C60)?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #19
    Re: Newbie - help with oddball setup

    A "regulator" is a generic term.

    A typical "regulator" on a generator is a Voltage Regulator.

    The current regulation is by design inside the generator itself (the amount of steel/iron, the way the windings are wound/connected, etc.) that the generator cannot physically output more current than is "safe" for the generator.

    I.e., like an Arc Welder--You "short the output" of the power supply to arc weld. The transformer (AC arc welders) or the design of the generator (and its control circuit) limits the welding current (and voltage to a degree).

    A circuit breaker is not a "current limit"--It is and emergency "off switch" if the current exceeds design specifications.

    Either your DC Generator is:
    • not designed to charge a battery bank,
    • the internal regulator of the generator is "broken" (regarding current limit/control),
    • your Circuit Breaker is too small for the genset,
    • the CB is broken,
    • your battery bank is larger (Amp*Hour rating) than the generator is deigned to support (a very large battery bank can draw very large amounts of current during charging and overheat many gensets/AC battery chargers that do not have over current limiting regulation), a smaller battery will be "forced" to 29.X volts with a large enough genset,
    • etc.
    Having issues with charging a large AH battery bank with typical consumer grade equipment is actually quite common.

    For AC consumer gensets (AC generators, or correctly stated AC Alternators), we recommend derating to 80% of name plate (or even derate more) because running many hours at rated load will "cook" the genset.

    Battery charging is very hard on wiring/breakers/generators (and alternators).

    For AC alternator systems--It is an easy fix. Just get a smaller AC to DC battery charger to limit the load on the genset (some modern AC chargers and many AC inverter-chargers are actually programmable--Very nice to find the "sweet spot" for running your smaller Honda/Yamaha gensets).

    For DC generator systems--You are in a bit more trouble... Your battery load is your battery load. You either have to get into the generator "guts" and figure out what it was designed to do. Possibly fix a flaky charge regulator/controller.

    Or worst case, put some ballast resistance in between the generator and the battery bank. Say your generator charges at 29 volts. And you want a maximum of (70amps*0.80 derate=) 56 amps charging the battery bank:
    • 29 volts - 24 volts minimum battery voltage = 5 volt drop
    • V=I*R, R=V/I, R= 5 volts / 56 amps = 0.089 ohms resistance
    • P=V*I= 5 volts * 56 amps = 280 Watts "waste heat"
    So, you need to build a ballast resistor bank that has 0.089 ohms and can disspate 280+ Watts to limit your genset output to charging a well discharged large AH battery bank (assuming 29 volt genset and 24 volt minimum battery voltage). You could even do this with XX feet of extra cable hung in free air (watch temperatures).

    Would I do a ballast resistor--Not really, it is not a very good solution--As the battery charges, the ballast reduces charging current--And slows the battery charging unnecessarily.

    You could also crank the generator output up to ~31-32 volts, and use a solar MPPT type charge controller. These are designed to limit output current. Put a 60-80 amp MPPT charge controller between the generator and the battery bank (and many high end MPPT controllers can be programmed for maximum output current to the battery bank) and use the MPPT controller as your "electronic ballast". It should work just fine (90% chance anyway).

    Anyway, going back through the thread--You calculated:
    I guess the genset is designed to operate a load - it is voltage regulated (user selectable between 26.6v and 32.3v) and will supply up to 2KW (71amps). If a load of more than 71 amps is applied, there is a CB that will trip to protect the genset.

    71 amps--The proper circuit breaker should be:
    • 71 amps * 1.25 breaker derating = 88.75 amps
    Or 90-100 amp rated breaker for this genset (with cabling rated for same current). You cannot use a Circuit Breaker to "regulate" output current of a power source. It is only there to protect the wiring.

    So, what rating breaker are you using (I may have missed it earlier in the thread)?

    Running a 70 amp breaker on this genset (assuming your numbers are correct) is a guarantee that you will pop the circuit breaker under normal use.

    Do you have a manual/link to the genset available?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #20
    Re: Newbie - help with oddball setup
    JR2980 wrote: »
    But what happens if the batteries are deeply discharged - they would try to suck as many amps as they could, lets say 100amps, and since the C60 doesn't limit the input current, wouldn't the batteries then attempt to draw that much from the genset, and immediately trip the 50amp CB (or cook the C60)?

    With the static load on there is not 100 Amps available to the C60, or even 71. There is only 71 Amps less the draw of the static load.

    You should always have over-current protection on the output of the C60, regardless of application, in case something goes wrong - including the C60 shorting internally and drawing current from the batteries.

    So you have the breaker on the gen set to prevent it being overloaded. You have the static load (with over-current protection too) to prevent there being too much current available to the C60. You have a breaker on the C60's input in case the static load fails (hopefully it will trip before the current exceeds the 60 Amps max - hence my suggesting limiting the current to 50 Amps). Finally you have the output of the C60 protected in case something goes wrong there. Four separate but inter-acting circuits, each with its own over-current protection.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #21
    Re: Newbie - help with oddball setup

    You could use the voltage adjustment of the genset to limit charging current to the battery bank... It may mean you have to change the voltage set point every 1 hour +/- to not exceed the generator's current rating.

    If this is only for "emergencies"--It will work OK.

    -Bill

    PS: The Amazon meter looks fine for the job.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #22
    Re: Newbie - help with oddball setup
    BB. wrote: »
    Either your DC Generator is:
    • not designed to charge a battery bank,
    • the internal regulator of the generator is "broken" (regarding current limit/control),
    • your Circuit Breaker is too small for the genset,
    • the CB is broken,

    The generator was definitely not designed as a battery charger - of that I am 100% sure. It was designed to supply power for 24v electronics - specifically radios and computers.

    Per the manufacturer, there is no current limit/control other than the CB - it was designed for static loads, so youwould never connect loads that would exceed the 71amps that its rated at

    The CB is the original CB from the manufacturer, and as far as I know is functioning properly (I havent loaded it more than 71 amps)

    BB. wrote: »
    • your battery bank is larger (Amp*Hour rating) than the generator is deigned to support (a very large battery bank can draw very large amounts of current during charging and overheat many gensets/AC battery chargers that do not have over current limiting regulation), a smaller battery will be "forced" to 29.X volts with a large enough genset,
    • etc.

    This is what I'm worried about - if my battery bank is deeply discharged, I may not even be able to charge it because just hooking it up to the genset, it will try to draw large ammounts of current, and immediately trip the CB. Thats why I'm trying to find a way to limit how much load is placed on the genset so that I can get as close to the 70amps as possible from the genset to the battery bank without tripping the breaker.


    BB. wrote: »
    Having issues with charging a large AH battery bank with typical consumer grade equipment is actually quite common.

    For AC consumer gensets (AC generators, or correctly stated AC Alternators), we recommend derating to 80% of name plate (or even derate more) because running many hours at rated load will "cook" the genset.


    This is not a standard consumer genset - it is a military genset that is rated to its full load continuously, so no need to derate



    BB. wrote: »
    You could also crank the generator output up to ~31-32 volts, and use a solar MPPT type charge controller. These are designed to limit output current. Put a 60-80 amp MPPT charge controller between the generator and the battery bank (and many high end MPPT controllers can be programmed for maximum output current to the battery bank) and use the MPPT controller as your "electronic ballast". It should work just fine (90% chance anyway).


    If that's the case, I can get an MPPT controller - I don't mind the extra cost if I know for sure it will work, but I don't want to spend that kind of money and just hope that it will do what I want it to do, then end up eating the coast if it doesnt work right, or even worse damage the several hundred dollar controller!



    BB. wrote: »
    Anyway, going back through the thread--You calculated:


    71 amps--The proper circuit breaker should be:
    • 71 amps * 1.25 breaker derating = 88.75 amps
    Or 90-100 amp rated breaker for this genset (with cabling rated for same current). You cannot use a Circuit Breaker to "regulate" output current of a power source. It is only there to protect the wiring.

    So, what rating breaker are you using (I may have missed it earlier in the thread)?

    Running a 70 amp breaker on this genset (assuming your numbers are correct) is a guarantee that you will pop the circuit breaker under normal use.

    I dont know specifically what breaker it has other than that its the original breaker from the manufacturer, and I spoke to the manufacturer and was told that it would trip at approx 71.4 amps

    BB. wrote: »
    Do you have a manual/link to the genset available?

    -Bill

    Yep - manual is available here..... http://www.deweyelectronics.com/assets/pdfs/misc/2kW-Military-Tactical-Generator-Sets-Technical-Manual.pdf

    The bottom of page 58 is where it talks about regulation and output supply - I've read it several times and understand some of it, but its definitely over my head!
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #23
    Re: Newbie - help with oddball setup

    Normally current is not regulated it is only limited. That's what circuit breakers and fuses are for. If the circuit is designed right they do not trip unless something goes horribly wrong.

    You do not want to use an MPPT controller on the gen's output. It will probably not like the 'quality' of DC it gets. Nor should you expect to run an inverter directly from it.

    If you are planing on a battery bank that can be charged at 10% capacity and that is <50 Amps there will be no problem with ordinary use. Key here is to prevent the batteries from being discharged too much. LVD set at system nominal is your friend there. 50 Amps current would do for a 500 Amp hour battery bank.

    Yes, if the battery is too deeply discharged or indeed if the circuit is shorted too much current may be drawn and the circuit over-current protection will be tripped. That's what it is there for.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #24
    Re: Newbie - help with oddball setup

    I can draw you a diagram once I get back from today's doctor visit. If I get back. :roll:
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #25
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    With the static load on there is not 100 Amps available to the C60, or even 71. There is only 71 Amps less the draw of the static load.

    You should always have over-current protection on the output of the C60, regardless of application, in case something goes wrong - including the C60 shorting internally and drawing current from the batteries.

    So you have the breaker on the gen set to prevent it being overloaded. You have the static load (with over-current protection too) to prevent there being too much current available to the C60. You have a breaker on the C60's input in case the static load fails (hopefully it will trip before the current exceeds the 60 Amps max - hence my suggesting limiting the current to 50 Amps). Finally you have the output of the C60 protected in case something goes wrong there. Four separate but inter-acting circuits, each with its own over-current protection.



    I guess I'm just dense.... whats limiting the current to 71 amps?


    Taking everything else out of the equation... static load, C60, and CB - if I connect a 100amp load directly to the genset what limits the genset so that it cannot supply the 100amps that its loaded with?

    My understanding was that in this scenario voltage would drop, and the genset would attempt to bring it back up by speeding up - eventually (pretty quickly I think) the engine would be unable to compensate enough and would stall, OR the alternator would overheat either way, you could never deliver that 100 amps - the generator would either stall everytime you connect it, or the alternator would be damaged and no more genset.


    Is that correct?


    Assuming that it is, whats different with adding the CB - it will simply trip so that the genset wont be damaged, but ultimately the result is the same; you'll never deliver the 100amps, and the batteries never get charged.


    Again, adding the CB and the C60, we would get the same result right? And the same again with the static load.


    If the batteries are deeply discharged and will suck up as much current as possible, I need a way to limit the amount of current that the batteries "see". They can want as much current as possible, but I need to regulate somehow whats available to them without overloading the genset.

    I get what you're saying with the static load will limit whats available from the rating of the genset, but it still wont change the fact that a deeply discharged battery could be trying to get 100amps, which would still trip the CB and the batteries would never get charged.


    Am I missing something - I feel like I'm over complicating it and maybe I'm just missing the one little piece that will make it all click in my head, but I just cant see it!


    I appreciate you all taking the time to try and educate me!




    Thanks!
    JR
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #26
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    Normally current is not regulated it is only limited. That's what circuit breakers and fuses are for. If the circuit is designed right they do not trip unless something goes horribly wrong.

    Absolutely - I actually understand this (score 1 for me!) :D

    But that's for static loads right?

    I was a radio tech in the Marines and we knew how much power our radios needed, and we made sure that we never exceeded the capabilities of the genset when using them - easy as pie because we knew exactly what the max load was for everything we were connecting to it.

    In this case, the load from the battery bank will vary depending on the state - deeply discharged would equal more load. How can I (or, can I at all) somehow limit how much of that load is placed on the genset?

    Cariboocoot wrote: »
    You do not want to use an MPPT controller on the gen's output. It will probably not like the 'quality' of DC it gets. Nor should you expect to run an inverter directly from it.

    Can you please explain this a little more? What would be wrong with the quality of the DC that is supplied by the genset? We've used these to power some fairly high tech mil-spec radios as well as laptops with no ill effects at all. They were specifically designed as a DC power supply for electronics, so why would there be an issue with the quality of the power?


    Cariboocoot wrote: »
    If you are planing on a battery bank that can be charged at 10% capacity and that is <50 Amps there will be no problem with ordinary use. Key here is to prevent the batteries from being discharged too much. LVD set at system nominal is your friend there. 50 Amps current would do for a 500 Amp hour battery bank.

    Yes, if the battery is too deeply discharged or indeed if the circuit is shorted too much current may be drawn and the circuit over-current protection will be tripped. That's what it is there for.

    I completely agree, and ideally would discharge no lower than 50% (40% tops), but stuff happens, and I'd still like to be able to charge the battery if it did somehow get discharged to deeply on occasion.



    Thanks!
    JR
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #27
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    I can draw you a diagram once I get back from today's doctor visit. If I get back. :roll:


    I would appreciate that - maybe it will make more sense to me that way.

    Being a Marine, I always did do better with pictures! :D



    Thanks!
    JR
    · Share on Twitter
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #28
    Re: Newbie - help with oddball setup
    JR2980 wrote: »
    Can you please explain this a little more? What would be wrong with the quality of the DC that is supplied by the genset? We've used these to power some fairly high tech mil-spec radios as well as laptops with no ill effects at all. They were specifically designed as a DC power supply for electronics, so why would there be an issue with the quality of the power?
    The problem with putting an MPPT controller onto a "stiff" DC source such as a generator or a battery charger is that the MPPT algorithm is designed to work with a limited current source like PV. Connect it to a generator and it will try to keep increasing the current it draws until it reaches the point where the voltage drop reduces the actual available power. That will kill a generator (or at least open the generator breaker.)
    SMA SB 3000, old BP panels.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #29
    Re: Newbie - help with oddball setup

    That Dr. visit took rather longer than I expected.

    Anyway, here's a basic diagram of what I am suggesting.

    The only way I can think of to limit current without breaker tripping is to use a coil and key (relay) so that if the current goes high it will change a part of the pathway to reduce the current to the battery through a resistor. That would be somewhat tricky to set up as there needs to be an 'on' and 'off' differential. It's how old mechanical "Voltage" regulators in vehicles worked.
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #30
    Re: Newbie - help with oddball setup
    inetdog wrote: »
    The problem with putting an MPPT controller onto a "stiff" DC source such as a generator or a battery charger is that the MPPT algorithm is designed to work with a limited current source like PV. Connect it to a generator and it will try to keep increasing the current it draws until it reaches the point where the voltage drop reduces the actual available power. That will kill a generator (or at least open the generator breaker.)

    Thanks for that info - I didn't realize that the MPPT controllers would behave that way. That being the case, then it definitely wouldnt work with the genset.

    How about using an inverter though? I still don't see how that would be a problem as long as I don't exceed the generators capacity.



    Thanks!
    JR
    · Share on Twitter
  • JR2980
    JR2980 Registered Users Posts: 14 ✭
    #31
    Re: Newbie - help with oddball setup
    Cariboocoot wrote: »
    That Dr. visit took rather longer than I expected.

    Anyway, here's a basic diagram of what I am suggesting.

    The only way I can think of to limit current without breaker tripping is to use a coil and key (relay) so that if the current goes high it will change a part of the pathway to reduce the current to the battery through a resistor. That would be somewhat tricky to set up as there needs to be an 'on' and 'off' differential. It's how old mechanical "Voltage" regulators in vehicles worked.



    Thanks for this info - setting up something like that is most definitely beyond my ability! I was really hoping that there was a charge controller or some type of regulator that would do exactly this but it seems that I may be out of luck on this.
    · Share on Twitter

Categories