Checking batteries under load?

bigk

How is the best way to check batteries for a load test? Thanks

BGW

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dereckbc

Poor mans way is with a bank of auto head lights, timer, and volt meter.

For example let say you have a 36 volt battery bank rated at 225 Ah (Trojan T-105’s). You want to put about a 25 amp load on the batteries, so 25 amps @ 36 volts = 900 watts. Now you want to find a combination of 12 volt head lights that total 900 watts in groups of 3. So let’s say you go to the auto store and find 100 watt car headlights. You will need 9 of them. Wire 3 in series, do the same with the remaining 6, then wire the 3 sets in parallel.

Charge the batteries, disconnect charger, connect head lights, start timer, connect volt meter across the batteries and wait until the voltage drops to 31.5 volts. When you reach 31.5 volts, stop timer, disconnect head lights, and now it is time to roughly figure out the capacity in Amp Hours using a calculator.

AH = T x L

Where:

AH = Amp Hour rating of the batteries under test
T = Time in hours and 1/10 like 8.5 hours
L = Load Current used in test.

So under ideal conditions using the example above, we know L = 25 amps, test ran 9 hours, so AH = 9 hours x 25 amps = 225 Amp Hours. But that will never happen, 7 to 8 hours is more realistice.

Or you could buy an Al Biers battery load test box, controller for around $40K to get real accurate and test to IEEE-455 standards for battery load testing.

scubabud

HARBOR FREIGHT

http://search.harborfreight.com/cpis...ry+load+tester

Tick-Toc

Andy4639

tonyton

We have one of those 19.95 battery load tester 6v/12v and it works great. Immediate results.
If it says bad, it's bad......

Nate

Bigk asked how to check batteries under load.

Drive the cart with a voltmeter hooked to them, do the entire bank or one at a time for individual readings as Andy suggested. This is the best for real life readings IMO.

If you want to load test them individually you can use a load tester like tonyton suggested. Still not a bad way to go, just take notes of start and end voltages and don't allow a battery to go below 5.5V.

What dereckbc did was capacity test the bank of batteries. I am not trying to nit pick but show the difference. Some batteries will pass load but fail capacity but if they fail load they won't pass capacity.

All good suggestions I just want to add to dereckbc's test it would be wise to monitor each battery. As the pack's total voltage reaches 34V start to measure individual voltages. If one battery is a little lower than the others a total voltage of 31.5 could damage it. Since this is just a test, time the pack to 33V total OR when one battery reaches 5.5V then stop test and clock.

I am playing on the extra safe side when I say 5.5V per battery, you will still get a very good idea what is going on.

scubabud

My FUEL gauge is a digital meter that is always on and measures the pack voltage during all use as well as sitting. Once stopped after driving around the voltage reading is usually .5 - .7 lower then what it will show after around 10 minutes. The round LED gauge was my first gauge and is kind of useless for accurate readings but the wife likes it. The readings show on the Digital Meter were after it just finished charging and didn't settle down to the normal 51 - 50.9 pack voltage. The gauge is $17.50 on eBay plus $2.95 shipping.

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Andy4639

bigk

Thanks everyone for your testing under load advice . Going to get to work and try some of these will post results .Thank's again ..

billbird2111

Love it. A thread from 2009 and I discover a Harbor Freight store in Sacramento, WITH the Battery Load Tester I need AND at the exact same price as the link above...

Nice!