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Eber's avatar
Eber
Explorer
Aug 21, 2013

Amp/hour test is way off-

I have installed two NAPA 8145's rated at 6v and 226a/h each.
I'm testing to see how long they last with an Isotherm C-85, 3c/ft, 12v refrigerator, consuming an average .8amps.

I assumed it would run almost 10 days on a charge.
Adding variables and other minor loads, at least 4 days.

After 24hrs., my voltminder reads 12.29 with compressor running.

Other known loads are the voltminder, small fan on Nature's Head which draws milliamps (?), and a indicator light on the new 4 stage charger/converter from Best Converter.

At this rate, they would need charging after about 30 hours or so.

Am I wrong in expecting too much? Math error? Other?

All lights have been converted to led and there's a 100w solar panel coming to keep batteries up. My only concern was the actual use of the refrigerator.

Yes, refrigerator was prechilled and contained three, 2liter bottles of ice.

Thanks for any help-

Eber

17 Replies

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  • Huntindog's avatar
    Huntindog
    Explorer
    Aug 21, 2013
    Huntindog wrote:
    I don't know anything about that fridge. But you mentioned that it has a compressor, and that it consumes .8 amps.
    Where did that figure come from?

    When a compressor starts up, it draws a lot more than it's running amps. And when batteries supply higher amps, the efficiency goes down.
    For example, some batteries are advertised as having 100 AH at a 1 amp draw... Simple math would calculate that a 10 amp draw would drain the battery in 10 hours....But it will actually drain it quite a bit faster than that.
    That coupled with not being able to tell just how many start up cycles are occurring will make the math difficult if not impossible.

    Also, the 226 amps each at 6 volts do not get added together when coupling two 6 volts to make 12 volts. You have 226 AH @ 12 volts, of which about 50% or 113 AH is usable....Depending on how hard you are wanting to be on the batteries. That computes to 5.8 days at a steady .8 amp draw. Which as I just said likely won't be a "steady" draw.
  • RoyB's avatar
    RoyB
    Explorer II
    Aug 21, 2013
    lots of unknowns here...

    Here is a simple chart showing batteries voltages verse state of charge
    This is NOT absolute but close for me to use when camping off the power grid.


    I usually start out my runs off the battery at 90% SOC and will run the loads until the battery banks drops to 12.0VDC which is close to 50% SOC.

    Then I must recharge back up to 90%.

    You should be above to run your batteries until they get down to the 40% charge state before doing harm to them. I just chose along with a bunch of others to start re-charging when the batteries get down to the 50% charge state.

    Insure you are starting you test with a good charged battery first...

    Roy Ken
  • time2roll's avatar
    time2roll
    Nomad
    Aug 21, 2013
    I suspect you have a combination of... other loads in addition to the fridge, new battery needs some cycles to reach rated capacity, and less than 100% charge.

    Let the solar charge for a week and test again. Or just let it run if the solar can keep up.
  • 2oldman's avatar
    2oldman
    Explorer II
    Aug 21, 2013
    Eber wrote:
    After 24hrs., my voltminder reads 12.29 with compressor running.
    What does it read with compressor not running?
  • Rbertalotto's avatar
    Rbertalotto
    Explorer
    Aug 21, 2013
    .8 amps???

    I can't believe a refrigerator can run on 8/10th of an amp?

    Is it on propane with just the thermostat and ignition running?

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