[RE-wrenches] Load testing batteries?

Mick Abraham mick at abrahamsolar.com
Wed Jan 26 07:19:48 PST 2011


Hello, Jesse~ Instead of trying for laboratory precision, here's a way to
measure the battery capacity using equipment that you may already own:

* Gather up appropriate safety stuff: gloves, goggles, baking soda,
distilled water, off duty fireman, blast protection, etc.

* Connect only two of the 6 volt batteries in series to make a 12 volt
battery string. Put those on charge once you're sure they're warmed up &
thawed out. Maintain about 75 degrees Fahrenheit air temperature in the
testing area. Recharge quality is important if you want to give the
batteries a fair opportunity to show what they can do.

* Install a DC breaker between battery positive and the positive DC terminal
on a 12 volt inverter. The inverter should be 500 watts or bigger with AC
plug in receptacles; you can connect inverter negative to battery negative &
power it up on the DC side.

* Plug into the inverter with an AC kilowatt-hour meter (such as
Kill-a-Watt, the Brand meter, WattsUp?, etc.) then plug into the kWh meter
with an adjustable blow dryer.

* Switch on the hair dryer at a low setting then dial up on the heat until
your AC meter shows about 360 watts of power draw. The battery pair, if new,
should be able to sustain a drain like this for about ten hours--this is
based on the 298 amp-hour rate for that battery on the Rolls spec sheet.

* Run the blow dryer until the inverter shuts off due to low voltage, then
read the number of AC watt-hours that were clocked by the kWh meter. 298 amp
hours X 12 volt nominal = 3,576 watt-hours. Battery professionals would
replace a battery if it fails to deliver 50% of the original rated power.

* Repeat this same test with the other battery pairs. As mentioned, this
approach is not scientifically perfect, but it might be done with minimal
outlays for new equipment...and the results will be close enough.

Jolliness~

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675


On Tue, Jan 25, 2011 at 10:53 PM, Jesse Dahl <dahlsolar at gmail.com> wrote:

> Wrenches,
>
> I have some (4) rolls 6 volt batteries 4000 series S-460. They are from a
> stand alone system in Ely, MN I have mentioned in a previous question. I had
> mentioned in the previous post that they were suspected to have been frozen
> (bulged cases).  The owner took them out of the system, dumped the
> electrolyte out and added new electrolyte.  I have no idea what she added or
> any specifics.
>
> I did a SG test today, all of the cells seemed to have 50% SOC, but I don't
> think that means anything.
>
> Most of the info I got from the last post and from my knowledge tells me
> the batteries are shot. They are 10 years old at least.  What I'm asking, I
> guess, is what type of load tester would a person need to load test a
> battery like this.  I have a cheap one, up 160Ah I believe, but I'm not sure
> if it will work this test.  I have limited battery experience and would
> appreciate any help with testing methods.
>
> Thanks everyone,
>
>
> Jesse
>
> Sent from my iPad!!!
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