Charging a florklift battery with a GC2 bank

jedon
jedon Registered Users Posts: 3 ✭
in Off Grid Solar & Battery Systems #1
I have an older bank of 16 GC2'a I want to use as a reserve for my forklift battery. When the forklift battery voltage gets low can I use a DC SSR + Diode to hook the GC2 bank to the forklift battery to charge it?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    edited October 2020 #2
    You can try it and see how it works.. 
    Your resting charged bank is resting at 12.7/25.4/etc. volts and your discharged bank is strong 12.0/24.0 volts.
    You may get some charging, but real charging is around 14.8/29.6 volts.
    You might just parallel the two banks for charging and discharging (assuming the charge set point voltages are similar) and see how it works.
    I am not a big fan of paralleling battery banks, but if you already have them and monitor voltages & specific gravity... Why not.
    If the batteries are different types (flooded cell vs AGM as an example), you should use the lower AGM charging voltage.
    If the two banks are very different regarding capacity (if smaller back is 20% or less of large capacity back), then it will be very difficult to even measure the added capacity of the smaller back.... And possibly not worth the effort.
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jedon
    jedon Registered Users Posts: 3 ✭
    #3
    Ahh good point about the charging voltages, they are both 48V banks, one is 16 GC2'a and the other is a 56kWh forklift battery so very different capacities although they are both FLA. 
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,113 ✭✭✭✭✭
    #4
    Isn't there a danger of explosion or generally bad things happening if there is a large difference in soc between battery banks when connecting them together?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    littleharbor2 said:
    Isn't there a danger of explosion or generally bad things happening if there is a large difference in soc between battery banks when connecting them together?
    Only if you let uncontrolled current flow.   Hundreds of amps even with small banks - one car battery can supply 300A to the starter motor in a car.
    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

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #6
    Nominally, you should only be looking at 12.0 volts low battery bank vs 12.7 volts for "charged" battery bank (or 48.0 vs 50.8 volts @ 48 volt bank)... Should not be a lot of current flow for an FLA battery to FLA battery (if this was Li Ion--Probably a different issue).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jedon
    jedon Registered Users Posts: 3 ✭
    #7
    It would be maybe 50.4 (GC2) to 48.7 (forklift), I suppose I could PWM the DC SSR to limit current. 
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