Date: Sun, 14 Aug 2011 11:52:07 -0500
Reply-To: Tom Hargrave <thargrav@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Hargrave <thargrav@HIWAAY.NET>
Subject: Re: Battery testing solution
In-Reply-To: <4e47f91a.c3b2340a.1c57.5690@mx.google.com>
Content-Type: text/plain; charset="us-ascii"
The resting voltage will tell you the state of charge but you need to know
the battery chemistry to translate. That's why the local parts store enters
the battery type before they test the battery.
Thanks, Tom Hargrave
www.stir-plate.com
www.towercooler.com
www.kegkits.com
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Edward Maglott
Sent: Sunday, August 14, 2011 11:35 AM
To: vanagon@gerry.vanagon.com
Subject: Re: Battery testing solution
I like your test, good idea. Won't the resting voltage of the
battery tell you it's state of charge? or is that less accurate?
Edward
At 12:24 PM 8/14/2011, Tom Hargrave wrote:
>Charging then putting a load on the battery for a specific time won't tell
>any more than the CC test will tell.
>
>But here is a test that will tell you something.
>
>Fully charge the battery.
>Put a known load on the battery - something like a light that draws 20
amps.
>Watch the battery until the voltage drops to 11.8 volts.
>Subtract the start time from the stop time then multiply the hours X the
>load.
>The result will be ampere-hours delivered.
>
>You need to do this test on a new battery right after you install it &
>record the result as a baseline then do the exact same test with the exact
>same load later when you expect a problem. And don't expect the results to
>be the same as what's marked on the battery. If you test again a couple of
>years later and the time is 20% less than your capacity has dropped 20%.
>
>Also, it's extremely important to use the exact same load. As load
increases
>the ampere-hours delivered decrease because more energy is turned into heat
>inside the battery.
>
>Thanks, Tom Hargrave
>www.stir-plate.com
>www.towercooler.com
>www.kegkits.com
>
>
>-----Original Message-----
>From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
>Edward Maglott
>Sent: Sunday, August 14, 2011 10:26 AM
>To: vanagon@gerry.vanagon.com
>Subject: Re: Battery testing solution
>
>I have thought about this many times. For our "house" batteries we
>don't really care about CCA, we are concerned about capacity. I have
>gently used various "inappropriate" batteries for my house battery
>over the years, like starting batteries or SLA batteries designed for
>UPS systems. I have found it hard to even find out the capacity of
>these batteries, they just advertise CCA.
>
>I have wondered what would be a good laymans way to determine the
>remaining capacity in these batteries as they age. Maybe
>this: Charge them up. Let them rest for a while to get a good
>resting voltage. Put a known load of a couple Amps on them for a
>fixed time. (Not discharging too low of course.) Let them rest
>again. Measure an ending voltage. Calculate something. There must
>be some Electrical gurus (like David B.) on this list who could
>devise a good method so that we don't have to buy that $3K analyzer.
>
>Edward
>
>At 10:17 PM 8/12/2011, Jim Arnott wrote:
> >"The purpose of battery testing is to estimate the end of battery
> >life. Automotive technicians are most familiar with CCA, a measurement
> >that reflects engine cranking but does not always predict the end of
> >battery life correctly. The leading health indicator of a battery is
> >capacity. So we ask, "At what capacity should the battery be replaced?""
> >
>
>http://www.ecnmag.com/Articles/2011/04/Design-Talk/Battery-Testing-at-Garag
>es-Simplified/
> >
> >
> >Go check out the article. See what $3k+ gets you....
>-----
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