Controller choice & dump resistance

SurfpathSurfpath ✭✭✭Solar Expert Posts: 393 ✭✭✭
I am putting together the components for an off-grid 48v solar/hydro system. Check out this link for more details on the project, including feedback from others. Because the principles concerning dump loads are similar, I figured this wind power thread fit my hydro question best.

In short, I expect my hydro to produce about 400w and I intend to run it about 5 hours a night. Complimenting this will be 1400w - 1800w's of solar, connected to a Flexpower 1-6 and a 450amp/hr (Rolls S600?) bank. I need to have solar because occasionally the stream dries up. However, I am installing the hydro first and willl see how much power I actually get from this before building too big/small a solar system.

My first question: Is the Morningstar TS-45 an appropriate dump controller for my project? I have already purchased this on NAWS, but I just wanted to be 100% sure.

My second question: I remember reading advice on a forum that one's dump load resisitor for hydro or wind needs to be at least as large as the entire system (ie. in my case my hydro + solar). I also remember reading on another forum (sorry, I dont have the links) that you only need a dump resistor as large as the maximum output of just your wind (or hydro) system. In simple terms..the solar takes care of itself, the dump resistor is really just for the hydro/wind. Which is right?

I don't plan to run both my hydro and solar at the same time. However, I'd like to know what size dump load resistor would be needed in case I need to simultaneously engage both systems.

By the way, I am thinking of a wirewound resistor such as this one (BTW - I think this site is a good find).
Thanks for the help.
Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.

Comments

  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Controller choice & dump resistance

    The TS-45 is a good dump-load controller. Kind of overkill on a 400 Watt generator @ 48 Volts though.

    The dump load only needs to be able to take the output of the turbine; the solar would be on a separate controller and will look after itself. The idea here is that the TS-45 will "monitor" the battery bank and feed power to the dump load if the Voltage climbs too much due to the hydro output.

    That resistor you cite is probably twice as large as you need, which is not necessarily a bad thing.

    Other forum members will no doubt have further input on this.
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance

    Answer to your first question: yes the TS-45 is fine for your setup.

    Answer to your second q is a bit more long winded:
    An important thing to note about dump load controllers and wind/hydro is that the hydro is effectively connected directly to the battery bank. The dump load controller is then also connected to the battery bank and watches the battery bank voltage, if the voltage is too high it diverts the excess to the dump. The reason I mention this, is because the dump controller is not aware of any of your other system components, all it sees is the battery voltage. So if you turn on your generator and set it to equalize at 65V and your dump load controller is connected to the battery, it will see the high voltage as excess and start dumping... result = your battery never reaches EQ voltage and you're potentially pumping your entire 6kW generator output through the dump loads.

    The same would apply to any other charging source you connect to the battery, which is probably why you heard that the dump loads need to be big enough for solar + hydro. If you have 1 dump load controller for hydro + 1 MPPT controller for solar then it won't be an issue as long as they both have exactly the same configuration. But if the configuration is different, the dump load controller has veto rights since it will just dump any excess power. For example, if your solar controller is set to absorb for 3 hours and your dump load controller is set to absorb for 1, your batteries will just get 1 hour absorb + 2 hours of dumping solar excess through the dump load.

    If you like horror stories have a read here: http://www.navitron.org.uk/forum/index.php/topic,17188.0.html this is what happens when a dump load is too small and isn't programmed to the same settings as the other charging sources.
  • SurfpathSurfpath ✭✭✭ Solar Expert Posts: 393 ✭✭✭
    Re: Controller choice & dump resistance
    stephendv wrote: »
    If you have 1 dump load controller for hydro + 1 MPPT controller for solar then it won't be an issue as long as they both have exactly the same configuration. But if the configuration is different, the dump load controller has veto rights since it will just dump any excess power

    Powerful example and well explained.
    Thanks.

    Basically: a system size equivalent dump load is cheap insurance against controller program mismatch.

    I noticed that in your link someone recommended a volt meter panel to track battery bank voltage. Perhaps a dump alarm on the Morninstar controller would also be useful. I think I'd want to know when my system was kicking out potentially large amounts of electricity to a heating element. Maybe there is a product that does this independantly.

    The other point you made regarding generator charging was less evident to me because I am new to this. Are you saying that, if I have to charge the batteries by generator (say there is not enough water or sun to equalize), then I have to make sure that both my controllers know that this is going on (otherwise they will dump to my resistors after 'regular' 48V is achieved)? I guess the answer is system-dependant & I need to first absorb the (outback & morningstar) manuals when I get them to figure this out. But is there a quick and dirty answer?

    Seeing those pics was a real eye opener. Wind/hydro is a wonderful compliment to solar, but I now see it needs to be carefully monitored.
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • SurfpathSurfpath ✭✭✭ Solar Expert Posts: 393 ✭✭✭
    Re: Controller choice & dump resistance

    As an addendum:

    I have found a neat link regarding employing a power resistor as a dump load, using the TS-45 controller as an example.

    If my hydro produces 400w and my solar (say) 1800w will just 1 resistor, like the below, do the trick?

    1 Ohm, 1000W, 5% Wirewound Resistor
    Attachment not found.

    Using Hugh's page: For a 48v system...

    Current = voltage/resistance = 60/1 = 60 amps.

    Next find the power it will have to dissipate (as heat).

    Power = voltage x current = 60 x 60 = 3,600 Watts.


    Power is 60 x 60 = 3600 watts


    Again, just checking....a 1000w 1 Ohm wirewound resistor can dump 3600 watts of power?? Is my math wrong?
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Controller choice & dump resistance

    solar should not need a dump load or need to be diverted.
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    Surfpath wrote: »
    Perhaps a dump alarm on the Morninstar controller would also be useful. I think I'd want to know when my system was kicking out potentially large amounts of electricity to a heating element. Maybe there is a product that does this independantly.

    Hmmm,not sure if something like this exists. Perhaps the TS-45 includes something like this? I know the MPPT version can send emails based on certain events, dunno about plain the TS version.
    Surfpath wrote: »
    The other point you made regarding generator charging was less evident to me because I am new to this. Are you saying that, if I have to charge the batteries by generator (say there is not enough water or sun to equalize), then I have to make sure that both my controllers know that this is going on (otherwise they will dump to my resistors after 'regular' 48V is achieved)? I guess the answer is system-dependant & I need to first absorb the (outback & morningstar) manuals when I get them to figure this out. But is there a quick and dirty answer?

    As long as all three chargers have the same voltage setpoints for daily charging, there won't be any issues. When you do an EQ charge, ideally all three controllers should have the same charge settings and should try to EQ at the same time. Alternatively, disconnect the dump controller and hydro while doing an EQ with the other two sources.
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    Surfpath wrote: »
    As an addendum:
    Again, just checking....a 1000w 1 Ohm wirewound resistor can dump 3600 watts of power?? Is my math wrong?

    Looks good to me :) with the caveat that you'd need a 60A rated controller to dump that much, but given your proposed system of 400W + 2kW of solar a 45A controller will cope. It won't however cope with 6kW from the generator- so as above, either disconnect the dump when charging with the generator, or make sure that all the controllers have the same voltage settings.

    While on the subject of same voltage settings, make sure that all three controller are using temperature sensors and that all of them use the same temperature compensation settings.
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Controller choice & dump resistance

    Does anybody ever read my sig? :p

    Surfpath is talking about a dump load for microhydro. His math is correct for this.
    The solar will be on a separate controller which will take care of that.
    When do you run the generator? When the hydro and solar output zilch power of use. Its output should also be regulated by the battery charger, therefor it should not produce any over-supply of power after batteries have reached the point where the dump controller would try to activate.

    Regulate each charge source on its own and they will co-operate. I see no problems with the proposed set-up.
  • BB.BB. admin Super Moderators, Administrators Posts: 29,632 admin
    Re: Controller choice & dump resistance

    Remember the shunt load is going to take power and generate heat regardless (pretty much) of what ever or how much anything is charging.

    Power = Voltage * Current = Voltage2/Resistance = Current2*Resistance

    Even if your battery is not being charged, the battery will supply energy to the load until the battery is dead (if you have, for example, a failed or miss programmed dump load controller).

    So, the load should be designed to operate continuously (for many hours) at rated load/power dissipation.

    A 1kW resistor should not be designed to dissipate 3.6 kW of power ever--It will turn red hot and catch nearby materials on fire and/or drop red hot debris onto the floor/next to the wall.

    Same thing with wiring (and even battery banks)--They need to be kept to maximum rated power per Code/Manufacturer even if you plan/assume the loads should only be active for a few seconds/minutes at a time.

    You do not want your system set for flaming self destruction if something goes wrong (hence why I and others here recommend following code for wiring and using fuses/breakers when needed).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    BB. wrote: »
    A 1kW resistor should not be designed to dissipate 3.6 kW of power ever--It will turn red hot and catch nearby materials on fire and/or drop red hot debris onto the floor/next to the wall.

    3.6kW is bigger than 1kW, thanks Bill I missed that one :blush:
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    Surfpath is talking about a dump load for microhydro. His math is correct for this.
    The solar will be on a separate controller which will take care of that.

    I too was under the misconception of how dump load controllers worked. There is no such thing as a dump load controller for hydro, because it's a dump load across the entire battery bank, and by implication it will dump all charging sources that try to charge that bank. In effect the battery, the dump load controller and the microhydro are all connected in parallel, which is quite different to how a PWM charge controller is connected! The dump load could be active even if the microhydro is producing 0W.
    This is why it's so important that all the charging sources have the same charging set points.
  • BB.BB. admin Super Moderators, Administrators Posts: 29,632 admin
    Re: Controller choice & dump resistance

    For example, using the 1kW resistor, place two in series and you would get:
    • P=V2/R= (60v)2 / (1+1 ohm) = 1,800 Watts across two 1kW resistors

    So, for this installation, you would use several paralleled resistor banks (2 strings in parallel would give you 3,600 watt dissipation) across 4 resistors. Or ~900 watt per 1kW resistor--OK--but you are running near the rated capacity. Need good cooling air flow and mount aways from flammable materials.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Controller choice & dump resistance
    stephendv wrote: »
    I too was under the misconception of how dump load controllers worked. There is no such thing as a dump load controller for hydro, because it's a dump load across the entire battery bank, and by implication it will dump all charging sources that try to charge that bank. In effect the battery, the dump load controller and the microhydro are all connected in parallel, which is quite different to how a PWM charge controller is connected! The dump load could be active even if the microhydro is producing 0W.
    This is why it's so important that all the charging sources have the same charging set points.

    It's all in the controller programming! :D
    Just ask waynefromnscanada.
  • SolaRevolutionSolaRevolution ✭✭✭✭✭✭ Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Controller choice & dump resistance
    stephendv wrote: »
    There is no such thing as a dump load controller for hydro, because it's a dump load across the entire battery bank, and by implication it will dump all charging sources that try to charge that bank. In effect the battery, the dump load controller and the microhydro are all connected in parallel, which is quite different to how a PWM charge controller is connected! The dump load could be active even if the microhydro is producing 0W.
    This is why it's so important that all the charging sources have the same charging set points.

    I recently installed a Kestrel wind generator with it's own controller. The controller actually has a diversion load that shunts off the wind turbine's energy when the batteries are above a setpoint voltage (on the high end of float voltage) rather than dumping power from the battery bus into the diversion load. It is so much better (at least in concept) than any other diversion load I have ever used. No interference with other charging sources. You can EQ with other sources, you can run the generator, get your regular solar absorb time settings, etc without having to fuss with brakes or breakers.

    I asked Derik at Hydro Induction Power about this design for micro hydro. He said he had looked into trying to get one of their controllers for testing but Kestrel was not interested in selling the controllers seperately.

    I look foreward to being able to use a 600 volt MPPT CC to regulate micro hydros. No diversion, No self destruct mode...Someday?

    Alex Aragon
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,415 ✭✭✭✭✭
    Re: Controller choice & dump resistance
    Surfpath wrote: »
    As an addendum:

    I have found a neat link regarding employing a power resistor as a dump load, using the TS-45 controller as an example.

    If my hydro produces 400w and my solar (say) 1800w will just 1 resistor, like the below, do the trick?

    1 Ohm, 1000W, 5% Wirewound Resistor
    Attachment not found.

    Using Hugh's page: For a 48v system...

    Current = voltage/resistance = 60/1 = 60 amps.

    Next find the power it will have to dissipate (as heat).

    Power = voltage x current = 60 x 60 = 3,600 Watts.


    Power is 60 x 60 = 3600 watts


    Again, just checking....a 1000w 1 Ohm wirewound resistor can dump 3600 watts of power?? Is my math wrong?

    NO you need a resistor rated for 3600 watts. Or 4, 4ohm resistors in parallel. Then you have the same issue as batteries in parallel, one resistor is going to be 4.02 ohms, and another 3.98 ohms, one burns out, then the next, then the last 2 - pop pop pop. And you have to provide cooling for the 3600w of heat coming off them too. So, lights come to mind. 500W halagon lamps, don't need cooling (not much) but have lifetimes in 100's of hours, so reliability is a concern, on the 3rd windy night, and you see the lights in the power shed are off....
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Controller choice & dump resistance

    i'm thinking to myself, why is it that nobody brought up what i'm thinking about this cited resistive load's resistance value? it would seem to me that loading down the turbine is important, but using a 1 ohm resistor with appropriate wattage rating will essentially short out the turbine. you might just as well have put the + wire to the - wire here and with a short or with that 1 ohm resistor all wires are going to heat before the turbine actually seizes or stops from the short. i'm not sure what the wind industry likes to use in reference to load values, but 1 ohm is too low imo.
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Controller choice & dump resistance

    Well I've obviously gotten confused about which system we're discussing here (again) but I thought it was for a 400 Watt wind turbine? In which case Niel point is well taken and the resistance value should be about 10 Ohms I'm thinking.

    Or maybe I've gone over the edge to "hopelessly confused" and should just stop answering questions altogether. :blush:
  • vtmapsvtmaps ✭✭✭✭ Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Controller choice & dump resistance
    Or maybe I've gone over the edge to "hopelessly confused" and should just stop answering questions altogether. :blush:

    or do what I try to do... read or at least skim through the whole thread before answering. It can be very frustrating because by the time I post my response Cariboocoot has usually beaten me to it. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Controller choice & dump resistance
    vtmaps wrote: »
    or do what I try to do... read or at least skim through the whole thread before answering. It can be very frustrating because by the time I post my response Cariboocoot has usually beaten me to it. --vtMaps

    On the upside I've never beaten myself to the post. :p

    I think I'll leave more of it to you, vt; you're good. :D
  • BB.BB. admin Super Moderators, Administrators Posts: 29,632 admin
    Re: Controller choice & dump resistance

    The idea of shorting the turbine output is that you will place so much load on the alternator, that you will stall the blades (turns too slow to generate much current).

    The issue with using turbine loading as the only speed control (in very high winds), is that some turbines have been known to cook the alternator with excessive current flow. Would a resistive load vs short circuit load be better--I don't know (it may depend--for example, if the wind speed is so high that a shorted alternator does not have the torque needed to slow the RPM and stall the blades--then you could have excessive current flow).

    In any case, this is why I always preferred the Dutch standard of having multiple, independent, methods of stopping/controlling a wind turbine. Much less chance of out of control RPM and catastrophic failures.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada ✭✭✭✭ Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Controller choice & dump resistance

    The little 5 foot diameter, PM alternator wind turbine I had was supposedly designed to be controlled in high wind by "stalling" the thing with a dead short on the alternator. In practice, it worked fairly well in average wind speeds, but during a storm with high winds, the blades ran away with the overloaded alternator and spun up, screaming like an insane banshee. And yes, after I took it down, I discovered the stator windings blackened and the plastic sleeves around the windings where they go through the stator core, were all melted. An extremely poor "braking" system indeed. Perhaps one could call it a breaking system.:D
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Controller choice & dump resistance

    you've got my thoughts exactly bill.

    good one wayne. another might be braking wind.
  • SurfpathSurfpath ✭✭✭ Solar Expert Posts: 393 ✭✭✭
    Re: Controller choice & dump resistance

    Good discussion. Thanks. There seems to be many folks who have combined solar with wind/hydro. It’s interesting to see the challenges.

    So, for my education, let me try and summarize some of the points made in relation to solar+hydro system under review:

    First, it’s evident (thanks Stephendv and Cariboocoot) that I have to be very sure that the charge points for the Morningstar TS-45 dump load controller are identical to the (proposed) Outback Flexpower 1-6’s.

    Second, if I have to charge my 450amp/hr battery bank with my 6kw genny because the hydro +/or solar are unable to adequately charge/equalize the bank themselves [note: the latter two may still be producing some electricity though], I should be OK still because as Cariboocoot said, the generator's output should “be regulated by the [Outback Flexpanel’s] battery charger, therefore [the generator] should not produce any over-supply of power after batteries have reached the point where the dump controller would try to activate.”

    Nevertheless, when the genny is charging I have to make sure my hydro is completely shut down. Because, unlike a wind generator(*), the hydro is directly connected “in parallel [Stephendv]” to my battery bank. Do I need to “shut off” the solar input as well?

    *[Aside: Hugh Piggots web page that I referred to, however, doesn’t seem to differentiate between wind or hydro input in his Morningstar 45 examples].

    Finally, in terms of dumping to a resistor, the Morningstar 45 is fine as the dump controller for my system. However if I plan to run both the hydro generator and the solar at the same time then, ideally, I need a resistor with a higher resistance value (ie. Ohm) than the one I listed my post. Cariboocoot mentioned something like “10ohms” of resistance.

    So, what would you pick as a dump resistor for this system? As an aside: Wirewound resistors appeal to me. I’m not that attracted to the idea of a water tank heater – I already have solar heated water. Unless I could dump to a small jacuzzi? Now we’re talking.;)
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    Surfpath wrote: »
    Second, if I have to charge my 450amp/hr battery bank with my 6kw genny because the hydro +/or solar are unable to adequately charge/equalize the bank themselves [note: the latter two may still be producing some electricity though], I should be OK still because as Cariboocoot said, the generator's output should “be regulated by the [Outback Flexpanel’s] battery charger, therefore [the generator] should not produce any over-supply of power after batteries have reached the point where the dump controller would try to activate.”

    Correct, as long as all the settings of all the charge controllers are identical, including EQ.
    Surfpath wrote: »
    Nevertheless, when the genny is charging I have to make sure my hydro is completely shut down. Because, unlike a wind generator(*), the hydro is directly connected “in parallel [Stephendv]” to my battery bank. Do I need to “shut off” the solar input as well?

    If all the settings, including EQ of all the chargers (outback vfx + outback fm + morningstar) are identical, including WHEN to do an EQ - then there's no need to switch anything off. Only if this is not the case, should you switch off the dump load controller. If there is ever a condition where the morningstar is using a different set of settings to the other 2 controllers, then you need to switch the morningstar off. The hydro itself doesn't matter, it's the dump load controller that'll throw things out of whack. No need to ever shut off solar.
    Surfpath wrote: »
    Finally, in terms of dumping to a resistor, the Morningstar 45 is fine as the dump controller for my system. However if I plan to run both the hydro generator and the solar at the same time then, ideally, I need a resistor with a higher resistance value (ie. Ohm) than the one I listed my post. Cariboocoot mentioned something like “10ohms” of resistance.

    Again, if all the controllers use exactly the same settings then the solar should not dump through the dump load even if it's running at the same time as the hydro. But mistakes happen and resistors are cheap, so I would size it to handle hydro + solar just in case. :)
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    I recently installed a Kestrel wind generator with it's own controller. The controller actually has a diversion load that shunts off the wind turbine's energy when the batteries are above a setpoint voltage (on the high end of float voltage) rather than dumping power from the battery bus into the diversion load. It is so much better (at least in concept) than any other diversion load I have ever used. No interference with other charging sources.

    Interesting! I think the midnite clipper controllers will work in a similar way. Morningstar's MPPT controller also have a programmable "Wind mode" available if you program them using the MSView software- but there's no additional PWM output available for a dump load, so I don't really understand how they're supposed to be used for wind. ?
  • SurfpathSurfpath ✭✭✭ Solar Expert Posts: 393 ✭✭✭
    Re: Controller choice & dump resistance

    Hi folks
    A quick update on the final choice of my dump load resistance bank. Please note: this is for a HYDRO turbine (not a wind turbine).

    To recap, From the previous postings here are a few salient points:
    Stephendv: "All the settings of all the charge controllers [must be] identical, including EQ."

    BB: "Remember the shunt load is going to take power and generate heat regardless (pretty much) of what ever or how much anything is charging. Even if your battery is not being charged, the battery will supply energy to the load until the battery is dead (if you have, for example, a failed or miss programmed dump load controller). So, the load should be designed to operate continuously (for many hours) at rated load/power dissipation".

    Stephendv: "There is no such thing as a dump load controller for hydro, because it's a dump load across the entire battery bank, and by implication it will dump all charging sources that try to charge that bank. In effect the battery, the dump load controller and the microhydro are all connected in parallel, which is quite different to how a PWM charge controller is connected!"

    I thought the idea of using large halogen lights was creative, but not as reliable as wire wound resistors. I would therefore like to build a bank of 300w 48V wirewound resistors like these. Each resistor is rated at 10.4 ohms.

    Now, here's the slightly tricky bit. Do I really need 9 or 10 of these green "torpedos"? to cover both the PV potential (1980watts) and hydro (est 150-200 watts)? That would be a lot of rubber that I'd have to import for my solar room.

    I had only intended to run the hydro in the evenings/night (don't want any plumbing misshaps when I am not at home during the day). Let's say sunset 6pm to 11pm. My turbine will be located closeby and it should not be inconvenient to turn it on and off. Whenever I need to charge the batteries from the generator I also intend to shut down the hydro and turn off the dump load controller.

    If I follow the above rules can I theoretically lower the size of my resistor bank? (BB's note above makes me concerned that I may not be able to do this).

    Suggestions?

    ps. As I posted before, water heating elements don't seem that great to me (I can see the set-up becoming a mosquito breeding zone, with rapidly evaporating water. Plus water heating is not a useful thing for me since it is warm all year round here).
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • stephendvstephendv ✭✭ Solar Expert Posts: 1,571 ✭✭
    Re: Controller choice & dump resistance
    Surfpath wrote: »
    Each resistor is rated at 10.4 ohms.

    Now, here's the slightly tricky bit. Do I really need 9 or 10 of these green "torpedos"? to cover both the PV potential (1980watts) and hydro (est 150-200 watts)? That would be a lot of rubber that I'd have to import for my solar room.

    IF you use a dedicated solar charge and an additional dump load charger, and both of their charging parameters are identical, then the dump loads just need to dump the power from the hydro. But if you decide to just use 1 diversion controller for everything then the dump loads needs to handle all the available power, solar + hydro.

    So if you go for option 1 and just want to dump the hydro then a 10 Ohm resistor will draw 4.8A at 48V, which is 230W. So with 2 resistors in parallel you'd be able to dump 460W. <-- Hopefully someone will check my schoolboy math here :)
  • SurfpathSurfpath ✭✭✭ Solar Expert Posts: 393 ✭✭✭
    Re: Controller choice & dump resistance
    stephendv wrote: »
    IF you use a dedicated solar charge and an additional dump load charger, and both of their charging parameters are identical, then the dump loads just need to dump the power from the hydro.

    Hi Stephendv. A dedicated dump load controller (a TS-45) has been purchased just for the hydro.

    Additional info that may clarify things: I think a small issue I face with this dumpload is how to balance safety/equipment protection concerns with cost concerns. Sure, it would be sensible to have a large dump bank that covers all situations. However, a large order of 10 wirewound resistors would need to be shipped to me (+ 100% tax, + tax on shipping, etc) = potentially $600.00, and a lot of hassle. Versus, say, 2 wire wound resistors that I can have a friend put in his/her luggage on a visit = $56.

    My plan all along was to run the hydro just at night. I don't know all the implications, or if there are other precautions I'd have to take (?), but perhaps this allows me a relatively safe (temporary) alternative?

    I realize that with time I am going to be tempted to run the hydro longer (I have heard the saying "your loads will grow"). But by then I ought to have slowly, and more economically, grown my dump bank to cover the entire system.
    -SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
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