[RE-wrenches] Load testing batteries?

Mick Abraham mick at abrahamsolar.com
Wed Jan 26 07:58:42 PST 2011


My "Brand" brand kWh meter has non-volatile capture of the kWh data even
when power is removed. I assumed that was true of the other kWh meters,
also, but one would certainly want to check on that point. Dan's other
points are helpful. If the clock is left out of the setup , one could still
get a useful capacity number for the batteries.

Batteries are rated in amp-hours...not watt-hours, of course, so there is
some conversion math to be done. Similar testing could be done with an
amp-hour meter on the DC side between battery and load...and that would be
more precise for a couple of reasons. My suggested setup does not account
for inverter inefficiency, for example, so it will tend to understate the
actual capacity.

The big advantage of my original suggested test rig is that the needed items
are less exotic and more usable for other purposes. If Jesse doesn't already
own one of those plug in watt-hour meters, he probably wants a good excuse
to get one. Ditto for the mini inverter.

Jolliness,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675


On Wed, Jan 26, 2011 at 8:42 AM, Exeltech <exeltech at yahoo.com> wrote:

> Once the electrolyte has been changed out, all bets are off for using SG as
> an indicator for state of charge.  Jamie Surette gave excellent commentary
> on a similar thread recently on how to handle a situation such as this.
>
> Mick's suggested procedure (below) will work, with caveats.
>
> Be sure you use a meter that records accumulated watt-hour usage in
> non-volatile memory.  You'll be connecting the meter on the AC-side of the
> inverter, and when the AC goes off due to low DC input voltage, the meter
> will go off as well.  The basic Kill-A-Watt meter (and perhaps others?)
> forget everything when the power goes off.   P3 (mfgr of the K-A-W meter)
> make a model P4460 that "remembers" values even when powered down.  Others
> likely do as well.
>
> I would recommend using incandescent lamps as a safer and more easily
> adjustable load.  Parallel three 100 watt lamps on a power strip.  With a
> meter (above) measure the actual power drawn by the lamps.
>
> As a backup "timer" for testing batteries, I use an ordinary analog clock
> .. the type with moving hands (remember those?).  Got mine from a big-box
> store.  It uses 3 watts, so is an insignificant load compared to 300-400
> watts.  Set the clock to 12 am and start your test.  The clock will stop
> with the total run time when the inverter shuts off.
>
> Speaking of inverters .. use a model that requires a manual reset after
> low-voltage shutdown.  Some types will automatically start back up if the
> voltage rises high enough again.  This could give you a bit of a false
> reading as to total capacity
>
> Be careful.
>
>
> Dan
>
>
> --- On *Wed, 1/26/11, Mick Abraham <mick at abrahamsolar.com>* wrote:
>
>
> From: Mick Abraham <mick at abrahamsolar.com>
> Subject: Re: [RE-wrenches] Load testing batteries?
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Wednesday, January 26, 2011, 9:19 AM
>
>
> 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<http://mc/compose?to=dahlsolar@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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