Time for Upgrade, Comments needed

dishxpertdishxpert Registered Users Posts: 22
Hello Forumites,

I have been away for awhile as my system has been running quite fine for the last 10 months except during spring when sun hours fell and my batteries wouldnt float. Now i am back as i need to upgrade my system and go tfully off-grid with some overall of course.

I entered into solar when my bill became ridiculous and was using 420KWH/month

Here's what i currently have:

* 5 x 230W CSP (29.2V/7.78A)
* 5 x 280W SunTech (35V/7.9A)
They are connected as follows 2pairs of 230W, 2 pairs of 280W, and a 230W/280W combo.

* 16 x 6V/225AH connected as 4 strings of 24V
* 3000W/24V Pure Sine Wave Inverter
*Outback FM80 Charge Controller.
* 6-circuit/30A prewired GENTRAN manual transfer switch (for load shedding)
*Midnite combiner & disconnect box.

These 10 panels lay on the south side of my roof at about 23o.

MY ISSUES
Even though i produce on average 8.7-11.2 KWH/dy of electricity, and the batteries FLOAT for 1-2 hrs each day, my shortfall per month is about 120KWH or 4KWH/dy.

* How many more batteries can i add to this system to offset the long float period and is it too late? (After 10 months).

* How many more panels do i need and how would i configure them since my FM80 can accommodate 2500W @ 24V? Or would i need another charge controller? i have an old TRISTAR 60A.

Please help me with the math to decide where to go.

Thanks a lot guys!!

Dishxpert
«1

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed

    First the standard reiteration that off grid power costs more than grid power just about any place in the world.
    Second the standard reiteration that conservation will return you more per $ than generation.

    Okay, that's been said and you still want to go ahead and produce 14kW hours per day even in Winter.

    What you've got: (5 * 230) 1150 Watts + (5 * 280) 1400 Watts = 2550 Watt array. On 24 Volts that could produce 81 Amps, possibly more.
    If you have that all on one FM80 controller it is already maxed out.

    Moreover, 2550 * 4 hours of sun * 0.52 efficiency = 5.3 kW hours AC per day, or approximately 1/3 of your stated needs.

    Four parallel strings of batteries on 24 Volt is already a bad idea. 900 Amp hours @ 24 Volts is good for up to about 5 kW hours.

    You would need about 3 times the array (where are you going to put it?) and 3 times the charge controllers and 3 times the battery bank and maybe 3 times the inverter.

    If you are serious about that 14kW hours per day you really need to go to a 48 Volt system and different (higher capacity) batteries.
    Vis:
    14,000 Watt hours / 48 Volts = 292 Amp hours * 4 = 1167 Amp hour battery bank. There you're looking at either 2 Volt cells or forklift batteries. You'd only need two charge controllers, but you'd still need about 7500 Watts of array.

    Sure you want to do this? Just how much are they charging you for utility power? $0.75 per kW hour? Is grid-tie with feed back possible?
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    Even though i produce on average 8.7-11.2 KWH/dy of electricity, and the batteries FLOAT for 1-2 hrs each day, my shortfall per month is about 120KWH or 4KWH/dy.

    Using your real world data, your 2.5kW of panels provide 8.7kWh/day worst case. If you need 30% more energy, then 30% more panels should do it. I would first increase the panels and see how it goes, then if you really need more battery you can add or swap in some more. The suntech's are a good voltage to use without an MPPT controller so you could shift these onto the 60A tristar and then use the outback controller for the existing CSPs, and the additional panels. The voltage of the CSP is common for grid connected panels so you shouldn't have a problem finding more at a good price.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed
    stephendv wrote: »
    Using your real world data, your 2.5kW of panels provide 8.7kWh/day worst case. If you need 30% more energy, then 30% more panels should do it. I would first increase the panels and see how it goes, then if you really need more battery you can add or swap in some more. The suntech's are a good voltage to use without an MPPT controller so you could shift these onto the 60A tristar and then use the outback controller for the existing CSPs, and the additional panels. The voltage of the CSP is common for grid connected panels so you shouldn't have a problem finding more at a good price.

    I know its not a good idea to have too many strings of battery of lower AH but my current 4 strings of 24V batteries starts floating by 12-1pm these days. Doesnt this mean i am wasting/dumping the sun's energy for 2 or so hours? If i am correct, why would it be preferrable for me to add more panels? Would i start floating by 11am instead of 12noon? Other than a cloudy/rainy day, i am a bit uncertain...
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Time for Upgrade, Comments needed

    please explain this statement as it is why we are thinking about more panels...
    "my shortfall per month is about 120KWH or 4KWH/dy."
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    I know its not a good idea to have too many strings of battery of lower AH but my current 4 strings of 24V batteries starts floating by 12-1pm these days. Doesnt this mean i am wasting/dumping the sun's energy for 2 or so hours?

    Yes it means you're not using all the available power from the solar panels. It also means that your overnight consumption was quite light, because your batteries charged up fairly quickly. Which begs the question, if the batteries are floating so soon, then where is the 4kWh shortfall coming from? Do you often run out of battery storage at night or on bad solar days?

    The reason I suggested more panels first, is that with more panels you add more available energy to the system for both good and bad solar days. If you add more battery capacity you only increase the capacity during bad solar days, and then you still sit with the problem of how to charge those batteries if the sun still isn't shining.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    My utility bill from the Electric company shows that i consume 120kwh per month which is about 4kwh/day.. I start

    Probably my batteries are discharging too rapidly in the evenings? They are US Power 6V/225Ah batteries. How long from 5pm is 900AH to carry me until 50% SOC?

    By 530 pm the panels are asleep so its all battery power from then on (i live in the Caribbean) . I usually start load shedding my appliances from 24.7 V and if it gets to 24.2V before morn then everything is off batteries though my fridge can make it through the nite but not the LCD and fridge.
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    My utility bill from the Electric company shows that i consume 120kwh per month which is about 4kwh/day.
    By 530 pm the panels are asleep so its all battery power from then on

    These two don't make sense together. Are you off grid? Are you using a charger connected to the grid? Where is that 4kWh going?
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    My utility bill from the Electric company shows that i consume 120kwh per month which is about 4kwh/day.. I start

    Probably my batteries are discharging too rapidly in the evenings? They are US Power 6V/225Ah batteries. How long from 5pm is 900AH to carry me until 50% SOC?

    By 530 pm the panels are asleep so its all battery power from then on (i live in the Caribbean) . I usually start load shedding my appliances from 24.7 V and if it gets to 24.2V before morn then everything is off batteries though my fridge can make it through the nite but not the LCD and fridge.

    Just to go back and get a clear answer from you on this:
    Are you not allowed to set up a grid-tied system?
    Or are you allowed to do this but do not get any credit at all for net power which you push back into the grid?
    Or is power so unreliable that you want to have the battery capability full time to avoid brownouts and outages?
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    My utility bill from the Electric company shows that i consume 120kwh per month which is about 4kwh/day.. I start

    Probably my batteries are discharging too rapidly in the evenings? They are US Power 6V/225Ah batteries. How long from 5pm is 900AH to carry me until 50% SOC?

    By 530 pm the panels are asleep so its all battery power from then on (i live in the Caribbean) . I usually start load shedding my appliances from 24.7 V and if it gets to 24.2V before morn then everything is off batteries though my fridge can make it through the nite but not the LCD and fridge.

    What else is running? Because a refrigerator and an LCD are not chewing up 5 kW hours over night.

    I suspect that you are looking at the daily output on the charge controller as the maximum power available from solar, and it isn't. Depending on how the AC to loads is wired, you could have some things on grid and some things off or a mixture of the two.

    50% capacity of the 900 Amp hours @ 24 Volts is 10 kW hours. At that point your battery Voltage would be 24 with no loads. If this battery bank is running out of power over night it is either trying to run something very large like air conditioning or else the wiring is bad and much of the capacity is going untapped. For four parallel strings you really need to use bus bars and equal length wires on all strings.
  • KeithWHareKeithWHare Solar Expert Posts: 140 ✭✭✭
    Re: Time for Upgrade, Comments needed

    Dishxpert,

    There is a big missing piece in your description
    dishxpert wrote: »
    ...
    * 3000W/24V Pure Sine Wave Inverter
    ...

    What is the inverter and how is it wired?

    Is this an inverter/charger and is it connected to the grid?

    What loads are running on the inverter?

    Keith
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Bill,
    My system is off grid with batteries until batteries dip below 24.7V below i start to load shed with manual transfer switch. In other words, the house runs on battery power from the sun goes down at 530pm until system starts to charge at 630am next day, almost 11 hours.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Keith,

    I have a Samlex 3000W/ 24V Inverter along with FM 80 charge controller and 4 strings of 24V @225AH battery banks in parallel to give 900AH.

    During the day i run the house (refridgerator, Desktop/monitor/stereo)
    During the night, its the fridge, 32"LCD, computer for a few hours and a few LED bulbs. These are wired to the inverter through a manual transfer switch to the house breaker box in order to load shed selected breakers.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Carib,

    I have no AC in house, no bus bars on banks, so probably the wiring on banks is bad. What test can i do?

    As i said, before solar, i would normally consume 12-14 kwh/day, now i consume about 4 kwh/dy on a 2500W panel/24V battery bank with 4 strings of 225 AH and FM80 charge controller.

    On the FM80 at 1450 EST, the total AH for today is 288Ah, 7.8Kwh, voltage in is 64V, voltage out is 27.4V and it is floating for 1 hour. Maximum output is 2260W.

    Can that help you to decipher what might be happening why i run out at nights?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    Keith,

    I have a Samlex 3000W/ 24V Inverter along with FM 80 charge controller and 4 strings of 24V @225AH battery banks in parallel to give 900AH.

    During the day i run the house (refridgerator, Desktop/monitor/stereo)
    During the night, its the fridge, 32"LCD, computer for a few hours and a few LED bulbs. These are wired to the inverter through a manual transfer switch to the house breaker box in order to load shed selected breakers.

    "Computer for a few hours". Desktop or laptop? There's a good 100 Watt difference between the two. Likewise the TV can use up to 200 Watts while on.
    Worst case: 300 to 400 Watts being used for these two items. * 5 hours would be as much as 2kW hours. A really bad refrigerator might use half that in 12 hours.

    No matter how you look at it, this does not add up to severe depletion of that battery bank.
    You should run everything you leave plugged in through a Kill-A-Watt for these over-night hours and see what sort of totals you get. The best thing you can do for yourself is chase down the power consumers and get rid of them, no matter what your electric source is.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    Carib,

    I have no AC in house, no bus bars on banks, so probably the wiring on banks is bad. What test can i do?

    As i said, before solar, i would normally consume 12-14 kwh/day, now i consume about 4 kwh/dy on a 2500W panel/24V battery bank with 4 strings of 225 AH and FM80 charge controller.

    On the FM80 at 1450 EST, the total AH for today is 288Ah, 7.8Kwh, voltage in is 64V, voltage out is 27.4V and it is floating for 1 hour. Maximum output is 2260W.

    Can that help you to decipher what might be happening why i run out at nights?


    First thing to check on the battery bank is the wiring method. Chances are they are "laddered". Look at the diagrams from Smart Gauge here: http://www.smartgauge.co.uk/batt_con.html
    For four strings in parallel the methods that work best are #3 and #4.

    The info on the power showing on the FM80 doesn't mean much when you switch loads from inverter to main. It really only shows the amount of power the charge controller has delivered. This is limited by both available sunlight and load demand at the time. You need to get some solid numbers on your total consumption to plan any expansion.

    Another helpful item would be a battery monitor. It will keep track of all the power going in/out of the batteries so you can get a much more realistic idea of the SOC at any moment, rather than relying on Voltage which is not that accurate. Some examples here: http://www.solar-electric.com/metersmonitors.html
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Carib,

    I just spoke to a local installer and based on what i am explaining to him, he concurs that the Outback charge controller voltage display is an unreliable method to determine SOC. He thinks at 24.2V on Outback i may be yet to get to 50% SOC. He is also recommending a trimetric meter. So, this may be my first move before i do anything else.

    What size shunt to get 100 or 500A?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Time for Upgrade, Comments needed

    The "smaller" the shunt (higher millivolts/amp) the more accurate it will be... However, if you have a large system, you need to worry about peak current (inverter, charge controllers, DC loads, etc.).

    So, a smaller system could get away with a 100 amp shunt, but that will, at best support a 600-1,000 watt load/charging source on a 12 volt system (without over loading the shunt--which is really just a precision power resistor).

    Also--You need to read the manual of the Battery Meter you wish to use... Make sure it supports the voltage bank you are/will be using, and allows you to program the correct shunt parameters for your meter/system.

    Our host, NAWS, points to this Delta (shunt) web page for the basics.
    Continuous operating current should not exceed 2/3 ammeter shunt rating. To ensure proper operation the shunt temperature is in no way to exceed 145°C, as a permanent change in resistance will occur.
    For example, if continuous current for an application is 500 amps, the ammeter shunt rating should be no less than 750 amps. This applies to both 50 and 100 millivolt current drop. To estimate minimum standard shunt rating required, divide continuous application amperage by .6666.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed

    Fortunately you have a 24 Volt system. The 3kW inverter should draw about 125 Amps at maximum output.

    One thing I recommend is that the low voltage disconnect (if applicable) be set to system Voltage. That way if it reaches 24 Volts while under load when the load is removed it will "rebound" and you will not have actually drawn your battery bank down to 50%.
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    He is also recommending a trimetric meter. So, this may be my first move before i do anything else.

    What size shunt to get 100 or 500A?

    I have a trimetric and like it. Get a 500 amp shunt.

    btw, Outback makes an excellent battery monitor, the flexnet DC. It costs more than the trimetric, but it integrates well with other Outback equipment and will allow you to do a few tricks that the trimetric can't do.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed
    vtmaps wrote: »
    I have a trimetric and like it. Get a 500 amp shunt.

    btw, Outback makes an excellent battery monitor, the flexnet DC. It costs more than the trimetric, but it integrates well with other Outback equipment and will allow you to do a few tricks that the trimetric can't do.

    --vtMaps

    Ah, but then he'd have to sell his Samlex 3kW inverter and by an Outback VFX3524.
    Not a bad idea, but not a cheap one either. :D
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Time for Upgrade, Comments needed
    Ah, but then he'd have to sell his Samlex 3kW inverter and by an Outback VFX3524.
    Not a bad idea, but not a cheap one either. :D

    I thought he had an fm80. When used with the flexnet DC the fm80 can terminate absorb by using the end amps as measured by the battery shunt.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed
    vtmaps wrote: »
    I thought he had an fm80. When used with the flexnet DC the fm80 can terminate absorb by using the end amps as measured by the battery shunt.
    --vtMaps

    He does and it would.
    But if you're going to "go Outback" ....

    You have to admit they make the most flexible, adaptable, best-interacting equipment there is.
  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Re: Time for Upgrade, Comments needed

    I'm hopping in late here, but this doesn't sound right, in any sense. Without A/C what are your major loads? fridge? hot water heater? Well pump? TV... I'm currently on grid and with limited use of A/C running at night when I'm home, with an electric water heater that is turned on and off manually, and a 12 year old fridge, and normal tv, light(compact floresents), use and a laptop ceiling fans... I use 11KWh a day, that's with the hot water heater and limited A/C so somethings not right.

    Have you reduced loads since trying to go solar only? What is the switch device from battery to grid? You stated somewhere "GENTRAN manual transfer switch", so you manually switch this or is it automated? perhaps switching when you have a high draw? I think a battery monitor might help figure things out. I take it you had some cloudy days with hurricanes? Were you switched "on grid" for a couple days? Is there a voltage at which you use electric from grid? I have a large battery bank, but If I have a large draw for 3-4 minutes I can make the apparent voltage drop to near or below 24V (my cabin system, a microwave while I have the A/C running will do it about a 1600 watt load)

    It's hard to imagine what your loads are that create a 14KWh per day use. I think you should look carefully at your loads.

    I wouldn't want more batteries, If you wanted to go with an outback inverter, I would seriously look at switching to 2 strings at 48volts, but of course the panels don't configure well for this, perhaps adding one (or 4 of the 230 watt panels for strings of 3 and put the 280's on the other controller)

    Under load the batteries will look much lower measuring the voltage than they truly are, if you have a simple volt meter or your inverter has a volt meter display, try microwaving some oatmeal(or whatever a cup of water, do put something in the microwave though...) in the morning before any serious charging is going on and see how low you go...

    Do know, that spring will come again, and if your off grid you must have either the array or some alternative charging for those cloudy days...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed
    First thing to check on the battery bank is the wiring method. Chances are they are "laddered". Look at the diagrams from Smart Gauge here: http://www.smartgauge.co.uk/batt_con.html
    For four strings in parallel the methods that work best are #3 and #4.

    Another helpful item would be a battery monitor. It will keep track of all the power going in/out of the batteries so you can get a much more realistic idea of the SOC at any moment, rather than relying on Voltage which is not that accurate. Some examples here: http://www.solar-electric.com/metersmonitors.html

    Hello Cariboocoot & All,

    I am back. I surprised myself and installed the Trimetric with 500A shunt to my system. I programmed P1 = 28.6V; P2 = 18.0A; P3 = 900AH

    By the usual 1-2 pm the batteries were fully charged so trimetric read 100%.

    Here is the surprising part. It was always in my head from an online battery chart that 50% SOC = 24.2V so i would not allow my batteries to drain below that voltage as read by the charge controller and usually started to load shed at 24.7V.
    Last night, when the trimetric read 24.7V the %SOC = 95 and when it read 24.2V it read 85%. However, for the first time i allowed my batteries to go as low as 22.5V as the trimetric read 78%.
    After 22.5V i started to load shed as i wanted to inform you guys and confirm that FLA batteries should really be allowed to drain to that voltage even if you are far from 50% SOC.

    I feel good but concerned out of unbelief........What to do?
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    Here is the surprising part. It was always in my head from an online battery chart that 50% SOC = 24.2V so i would not allow my batteries to drain below that voltage as read by the charge controller and usually started to load shed at 24.7V.
    Last night, when the trimetric read 24.7V the %SOC = 95 and when it read 24.2V it read 85%. However, for the first time i allowed my batteries to go as low as 22.5V as the trimetric read 78%.
    After 22.5V i started to load shed as i wanted to inform you guys and confirm that FLA batteries should really be allowed to drain to that voltage even if you are far from 50% SOC.

    22.5 volts is too low. What sort of currents are you drawing when you report these voltages? You need to calibrate your battery monitor by measuring specific gravity (SG) of your battery cells. If you lie to your battery monitor it will lie to you. Do you really know what the AH capacity of your batteries is? Not the manufacturer's ratings, but the actual capacity of your somewhat used batteries. The only way to know is to measure SG. If you don't know your capacity neither does your battery monitor.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed

    First of all, Voltage is not an accurate measurement of SOC. But when it's all you've got it's what you use. As a rule, 24 Volts being 50% SOC is in reference to resting Voltage, not the Voltage read on an active system. In other words if you disconnect the batteries from everything for a few hours and then measure 24 Volts the batteries are about 50% SOC.

    The thing you need to do is check the accuracy of the Trimetric by comparing its SOC numbers to specific gravity readings. There are things that can throw a battery monitor off, incorrect programming being #1 of course. Sometimes it is incorrect even though you've done it right; installing a monitor on old batteries and setting the capacity for their full capacity is one way. Getting the efficiency wrong is another. I'm not sure setting P1 at 28.6 is correct either. That sounds like Float Voltage and I think it's supposed to be set for resting Voltage (25.5). Someone who's done one of these recently will be better informed about it. I also think the Amp hour is supposed to be the usable capacity not the total. Another thing someone else needs to check for us.

    The other thing that is important is that the batteries are wired properly. Yes, I've already gone on about this. But it's possible to have the system using basically only one string of batteries fully (and the others partially) and the monitor thinks it's 900 Amp hours when it's really only a portion of that.

    Despite the lack of analog correlation between active Voltage and SOC, I share your concern that your monitor is reading optimistically in light of the Voltage readings. This needs to be triple checked before things get worse.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Now, i am worried. How low a voltage should i then go?

    Prior to now i was being asked where is my stored energy going why i am using so many KWH from grid per day (4kwh).

    I was beginning to feel happy that my batteries were being underused as i didnt allow the voltage to drop below 24V. Now, 78% is not equal to 22.5V. How do i calibrate my battery banks after measuring SG?

    More questions than answer!!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Time for Upgrade, Comments needed

    Got a hydrometer? Many of them have an easy-to-see green/white/red zoning on the float. The green (good) starts at about 1.265. The white (fair) at about 1.200. You can consider that as 50%, but first get the green lined up with your monitor as what state is fully charged. If the monitor was programmed and set to work at a point when the battery was actually less than fully charged it will think that the battery is charged when the SG reads 1.225 for example - because that's where it started and was 'told' "this battery is fully charged".

    Using 24 Volts as a cut-off point is a simple short-cut for saving batteries. Technically that would be 50% of a resting Voltage. As an active Voltage it ensures the battery will not actually be pulled down below 50%. Once loads are removed the Voltage will rebound. How much depends on how heavy the loads are. This is what vtMaps was referring to: if you are measuring lower-than-normal Voltages even though the monitor says you have 78% SOC it can be due to heavy loads drawing the Voltage down (this doesn't have as immediate an affect of SOC as it does on V).

    I wish the monitor makers would include a very detailed set of instructions for initial install and calibration. I believe there's an input number for efficiency as well? And like vtMaps said, you've lost some capacity already because they are not brand new batteries.
  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    More questions than answer!!

    That's cool, when we have 'Dish' questions we'll ask you!

    I saw a $10 glass hydrometer that looks very much like the one I use at O'Rielly's auto parts, I bought a spare and it matches mine.

    I'd set the low voltage cutoff to @23V for now, if you have heavy loads, like a microwave that run with other household items running. I believe P1 represents the point that tells the meter you've reach full charge and you should set it just below your daily high absorb voltage. I think P2 and P3 are set correctly for a 900 Ah battery bank, with 4 strings it is almost a certainty that one string will react quicker than the others and this will become greater as they age.

    It's not uncommon to set the battery banks capacity to less than the battery rating. Some set it to represent only the capacity they are willing to use, like 50%.

    All this is from my faulty memory, so check it out and corrections encouraged! Hope I'm not just one of those open forum idiots...lol
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed
    Photowhit wrote: »
    That's cool, when we have 'Dish' questions we'll ask you!

    I saw a $10 glass hydrometer that looks very much like the one I use at O'Rielly's auto parts, I bought a spare and it matches mine.

    It's not uncommon to set the battery banks capacity to less than the battery rating. Some set it to represent only the capacity they are willing to use, like 50%.

    All this is from my faulty memory, so check it out and corrections encouraged! Hope I'm not just one of those open forum idiots...lol

    Hey Photowhit,
    I bought a hydrometer some time ago but unfortunately, i cannot find its rubber tip. Will have to repurchase. Is there a derating factor that one can put on their batteries with each passing month or year based on 50% discharge?

    Probably i will hold strain at 23.7V for now while discharging!! What ref value do you guys with 24V system use? Today is the first full day of trimetric use so hopefully i will get better data with each passing day..
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