Battery discharger

gicamucigicamuci Registered Users Posts: 30 ✭✭
Any idea what to use to discharge a single 6V 225Ah lead acid battery so it won't take forever ? Not looking for something high-end or such, but just something I could use and maybe I would have it around.
5.1kW, 12 × 250W + 4 x 275W + 3 x 330W (driving the pool pump MPPT controller or charging batteries on cloudy days) solar panels , FM80 MPPT CC, WavePower 6kW pure sine inverter, 16 x Trojan 105Plus in 8s2p strings 450Ah @ 48V battery bank.
8Kw Champion LPG gen for emergencies only.


  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Might get a 12 volt car heater, It should work at about 1/4 the rated power for 12 volt on 6 volts.

    They may have a low voltage disconnect that you would have to bypass.

    So on 6 volts it should be about 38watts, drawing 38/6=6.2 amps. Any straight resistance load should work. 

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Lots of ways to address the question...

    Say you wanted a 20 amp draw (10% of AH capacity)...
    • V=IR
    • V/I = R = 6 volts / 20 amps = 0.3 Ohm power resistor
    • P=V*I=V^2/R=I^2*R= 6 volts * 20 Amps = 120 Watt power dissipation...
    Find some power resistors that series/parallel to 0.3 Ohms and can dissapate >120 Watts--That would work.

    So would other "non-traditional" loads... Roughly 200 Feet of 12 AWG cable laying around on a 6 volt battery will draw about 20 amps... If you have a spool of wire, re-spool in loose coils for air circulation:

    • 12 AWG wire is 1.588 Ohms per 1,000 feet (rough number)
    • 0.3 Ohm load / 1.558 Ohms per 1,000 feet = 0.189 1000 ft = 189 feet
    6 volt light bulbs... Here is a 40/45 Watt bulb for old cars and motorcycles:
    Get 3-4 of those bulbs for $6 each--Connect them in parallel and you have your load bank.

    All the above numbers are approximate... Some things like 189 Feet of #12 AWG cable is a bit shade tree mechanic... And you should verify the actual current--And make sure the wire does not overheat.

    Your battery may start at 6.4 volts charged and end up at 5.25 volts dead--So current will vary.

    Neat things about filament lamps--They are sort of a constant current drain. When the filament is white hot, the resistance of the filament is relatively high. When the battery voltage drops and the filament starts glowing more towards they yellow/red spectrum, the filament resistance drops.

    Of course, there are lots of electronic battery testers/load banks... Ranging from $50 to $250+... I looked around, but it was difficult to find the specification/details to see that it could support 20 amps @ 6 volts (0.3 Ohm) and 120 Watts for hours on end (some seem to indicate continuous discharge of 25% of "rated watts").

    Any of this help?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,359 ✭✭✭✭✭
    i used to like sealed beam automotive headlamps.  When one element burned out, i had a new Load for things using the filament that was still good (usually the high beam)
    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

    gen: ,

  • TecnodaveTecnodave Registered Users Posts: 437 ✭✭✭✭
    I have used sealed beams in the same way....also industrial filament bulbs for higher voltages, but as mentioned resistance will vary with voltage/Temperature
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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