50v battery bank?

n4wff
n4wff Solar Expert Posts: 48 ✭✭
in General Solar Power Topics #1
I have been playing with 2 used 36v forklift batteries for a few weeks now. After selecting the strongest cells and bypassing the bad ones with jumpers, I have a good string of 25 cells. On my 48v system, is there anything wrong with keeping the battery bank at 50v and raising the float, absorption, and equalization voltages up on my inverter and charge controller? With the new settings, float = 55, absorption = 60.4, and equalization = 63.9. I can go back to 48v, but I would have to cut another factory jumper which I did not want to do unless I had to.
On a side note, the original amp hour capacity was 930 when new, would this new bank be equivalent to a 969ah 48v bank? (930/24x25=968.75)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: 50v battery bank?

    The only issue is (usually) the maximum AC inverter (and sometimes battery charger maximum output voltage--especially backup AC battery charger) ability to run at "+2.5 volts"... As long as your devices can operate at the equalization voltage (or you can live with shutting down the inverter during absorb)--You should be fine.

    Yes, the additional cell adds voltage (not AH directly)--But the overall energy storage is 25/24 times larger (in terms of kWH of storage).

    With higher voltage battery banks, be sure to monthly (or weekly) take a volt meter and check the voltage across each cell... It is very easy on a "higher voltage" battery bank to "lose a cell" (i.e., a cell becomes shorted) and not notice it in day to day operation (everything works fine, but the rest of the cells become over charged/shorted cell may overheat during operation).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n4wff
    n4wff Solar Expert Posts: 48 ✭✭
    #3
    Re: 50v battery bank?

    Thanks Bill. My XW will accept up to 64v DC so I am OK on the voltage. With so little extra capacity it wouldn't be economical to buy an extra cell, but since I already had it, I hated to waste that extra cell.

    - Jack
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: 50v battery bank?

    If your system works well with the "extra cell"--I would use it...

    Otherwise, you are looking at trying to find/make a 2.xx volt battery charger with at least 9 amps output (regulated, or just put a lamp timer that runs, for example, a couple hours a day) to float the cell. Otherwise, a "real" 90-200 amp 2 volt battery charger--Not sure one exists outside of a battery mfg...

    Electrically, it is not that difficult to design/build a 2 volt current limited battery charger--But it does take effort to do it. And finding a 10 amp current limited charger that would work for this project off the shelf--A bit more difficult (if not impossible)...

    I wonder if you can contact a battery distributor to find where they get there (if they can), and/or if they have one the could sell you used at a good price.

    There are other ways of current limiting--A filament lamp is great, but it is very inefficient.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n4wff
    n4wff Solar Expert Posts: 48 ✭✭
    #5
    Re: 50v battery bank?

    I just checked and it cycled through absorption, and is now in float holding steady at 55v, so everything seems to be working. Later I will try to equalize and see what happens.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #6
    Re: 50v battery bank?
    n4wff wrote: »
    I just checked and it cycled through absorption, and is now in float holding steady at 55v, so everything seems to be working. Later I will try to equalize and see what happens.

    If you equalize with SCC and the battery temperature is below 25C, it will not temperature compensate above 64V. You can fix it by re-programming it to nominal 60V bank.
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  • n4wff
    n4wff Solar Expert Posts: 48 ✭✭
    #7
    Re: 50v battery bank?

    I had forgotten about the 60v setting. I just tried it and the system would not let me set the equalize voltage to anything but 72v. Possible firmware bug? I could change the values for everything else. If I go back to the 48v setting, and as a work around, I set the default battery temperature on the charge controller to warm, and then connect the battery temperature monitor to the inverter only. I rarely put over 50a charging into the batteries from the solar panels anyway so I do not think overheating the batteries will be a problem.
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  • n4wff
    n4wff Solar Expert Posts: 48 ✭✭
    #8
    Re: 50v battery bank?

    Update, The Combox menu has the bug in it. I can change the voltage manually from the menu on the charge controller. 67.5v is the lowest I can set it. It is within the 70v safety cutout for the XW, but a little too high for the battery bank. Back to the 48v setting.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #9
    Re: 50v battery bank?

    Any way to manually equalize, or program with a SCP? Manually, change the absorb voltage, and monitor it for a DIY EQ setting, then switch it back.
    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 ,

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  • n4wff
    n4wff Solar Expert Posts: 48 ✭✭
    #10
    Re: 50v battery bank?

    The SCP is hard coded and will not let you go outside its programed range. Also 48v is the highest you can set low battery cutout. I do like the the idea you had to manually equalize. During the cooler months, I think I can set the bank voltage to 60v and run the absorb voltage up to equalize, then set it back to 48v for normal operation. I wouldn't do it with new batteries, but I am willing to take a chance on these old cells.
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