Multiple battery bank with different capacity or chemistry

AGB
AGB Registered Users Posts: 40 ✭✭
in General Solar Power Topics #1
Is there any BMS out there that can combine multiple batteries with different capacity and or different chemistry to be use on a single load? For example having a 24V or 48V Lead Acid and LiFe connected together by a single BMS.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #2
    The BMS is not really the problem, it is the differing electrical profiles for these batteries (charging and discharging voltages vs state of charge).

    Keeping each bank separate (by chemistry) and using (for example) AC inverters or DC to DC converters to createa coming power bus would be the only "good" method I can think of to mix and match something like this.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • AGB
    AGB Registered Users Posts: 40 ✭✭
    #3
    Better yet, maybe a charge controller that can charge two separate battery banks simultaneously with different charging profile and then use relay to switch between the battery bank depending on the state of charge.
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #4
    AGB said:

    Is there any BMS out there that can combine multiple batteries with different capacity and or different chemistry to be use on a single load? For example having a 24V or 48V Lead Acid and LiFe connected together by a single BMS.

    No. You can still do it but it's not that straightforward. Each battery has to have its own BMS (if it's a lithium chemistry, that is.) You can combine their outputs if their discharge curves sort of match. For example, you could combine a 48V li-ion and 48V lead-acid and get reasonable performance during discharge. They wouldn't discharge at the same rates, but by the time you hit about 44 volts both would be fully discharged. You'd have to charge them separately, though - the li-ion would want 54.6 volts and the lead acids want 58.4.

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  • AGB
    AGB Registered Users Posts: 40 ✭✭
    #5
    bill von novak said:

    AGB said:

    Is there any BMS out there that can combine multiple batteries with different capacity and or different chemistry to be use on a single load? For example having a 24V or 48V Lead Acid and LiFe connected together by a single BMS.

    No. You can still do it but it's not that straightforward. Each battery has to have its own BMS (if it's a lithium chemistry, that is.) You can combine their outputs if their discharge curves sort of match. For example, you could combine a 48V li-ion and 48V lead-acid and get reasonable performance during discharge. They wouldn't discharge at the same rates, but by the time you hit about 44 volts both would be fully discharged. You'd have to charge them separately, though - the li-ion would want 54.6 volts and the lead acids want 58.4.

    That is the kind of solution I am looking for. I was thinking to combine lead acid and li-ion. What device would you use to combine the output?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited October 2018 #6
    AGB said:



    That is the kind of solution I am looking for. I was thinking to combine lead acid and li-ion. What device would you use to combine the output?

    I don't think it will work, without some real expensive stuff, that has yet to be invented.

    You could do it with 2 charge controllers, 2 arrays, and some sort of 400A MOSFET's to act as a super diode to combine the banks.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited October 2018 #7
    The charging and dischargeing curves are so far apart, the notion of combining the two in any sort of symbiosis is absolutely unrealistic, they should be isolated from one another at the DC level.



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