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One Solar charge controller-Two separate 48V LifeP04 banks

teecomp

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Feb 26, 2021
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I have just purchased an 80amp MPPT 250V Growatt SCC. I plan on purchasing 2 365 Rich Solar 335W panels which I want to use to charge separate 48V 304AH LifePO4 banks for powering electric boat motors (no inverter involved) . Would it be possible (and safe) to use a A/B battery switch to manually chose which bank to charge? Thanks for any guidance.
 
That would work, but you could charg both as well.

It is generally a good idea to disconnect the solar before playing with the DC side of the controller. Consequently, you may want to add a disconnect switch on the solar side.
 
Thanks. It is my understanding that I would have to have a SCC capable of running dual battery banks and research on this forum led me to believe that they are hard to find.
 
It is my understanding that I would have to have a SCC capable of running dual battery banks
Will the two banks be used together, or will they be used separately? As long as they are charged and discharged together I do not know why you would need two controllers. If they will be discharged separately, it is a different story. When you hook two different batteries with different SOC, there will be an initial rush of currents while the SOC balances out between the two.
 
The battery banks are completely separate.
OK, if they are to be charged and discharged separately, then you probably do want to either keep them on separate controllers or use the same controller on one battery at a time.

If you do decide to use an AB switch, be sure to switch off the solar input before switching the batteries.
 
Thanks FilterGuy for the advice. Another question. I purchased Overkill 100a 16s 48v BMS for each battery bank. Does the BMS amperage need to be sized to the 304ah banks or the motor load (20kw 400aDC)?
 
Thanks FilterGuy for the advice. Another question. I purchased Overkill 100a 16s 48v BMS for each battery bank. Does the BMS amperage need to be sized to the 304ah banks or the motor load (20kw 400aDC)?

The BMS is sized for your loads. You could have a 5000 Ah battery, but only a 100 amp BMS if your loads never exceed 100 amps.
 
So if the specifications for my motor indicate: current 400Adc maximium input 20.0 kw, will this 100a overkill BMS work? Or is it undersized and would only allow a fraction of the motor capacity to be used? Would I need to wire multiple BMS's in series to reach the proper operating amps?
 
current 400Adc maximium input 20.0 kw, will this 100a overkill BMS work?
A 100A BMS will hit high current disconnect condition at 100A current and disconnect the battery. This would not be good, your BMS may not survive doing this, certainly not regularly.
 
At stated above, a 100 amp BMS isn't going to cut it. You'll want at least four BMS, wired in parallel (not series), to satisfy what your motor can pull.

You have two batteries already, so two BMS. Your options are to add two more batteries, each with it's own BMS, or you can install two BMS on each battery. The two BMS on a battery option is not what I would do, but there are a handful - at most - of forum members that have done just that. One forum member did and then decided against it after a period of time in use.
 
So I have two banks (each with 16 cells) that i was going to wire in series to make a 48v battery with a single 48V bms. It appears that instead I need to wire 4 cells in series to make a 12v with its own 12v 4s bms, and then series each 12v battery to the other three, which will each have a 12v 4s BMS. Correct? Ouch on my unexpected BMS budget!
 
No you need a 48 v battery- not four 12v batteries (if you wire up four 12v batteries in series with their own 100a bms you would have one 48v battery with a 100a capacity bms.

Here is probably a better idea - wire the 400a motor to a contactor (big relay) (like Kilovac EV200AAANA (that one is 9-36v - which is on my RV) the 48v is EV200ADNA or EV200AJNA or a gigavac - don’t know their products) then the bms controls the contactor. That can handle 500a. (Be sure and kill the motor before the bms disconnects (or connects) the Kilovac - or it will not last very long).

That motor is 48v - so you need a 48v battery. You probably need to put a 1000a shunt on that battery to keep track of its power level - like a Victron BMV712 (w/1000 shunt).

For the solar it would probably be better to connect a SCC (solar charge controller) to each battery, if you need to share panels find a DPDT switch (that can handle the volts and amps) then switch the solar panels between the two batteries. (You might be able to do that with two blue sea on-off-on battery switched -maybe even one if the negatives are tied together- but I do not know if that would be good???).

Just wanted to make sure you realize - those panels will not charge up that battery very fast - probably 3 to 4 days - while that motor will drain that battery in probably 30 to 45 minutes. (My guess is you need more solar and a bigger battery, you may also want a more capable BMS. (Look at Batrium).

Good luck with your project!
 
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