Your AH load testing will be optimistic realtive to the actual loading done
by driving which will have much higher currents than 6 oe 7 amps. My
OdysseyPC1500 nominally rated at 55AH derated to 16AH if discharged in 2
minutes. The 30 minute or 85A laod derates the battery to 42AH. me
by driving which will have much higher currents than 6 oe 7 amps. My
OdysseyPC1500 nominally rated at 55AH derated to 16AH if discharged in 2
minutes. The 30 minute or 85A laod derates the battery to 42AH. me
SLPinfo.org <[email protected]> wrote:
> HI folks,
>
> I've been struggling with how to determine how much life is left in my AGM
> batteries. The classic test that a battery shop does is a "load test", but
> I had heard that such a test was not very meaningful for deep cycle
> batteries. Some test of AH capacity needs to be done. But I was never
> sure
> how to do it until recently. Now that I have a method, I've tested all all
> the batteries I have (both the ones I was using and a group of used ones I
> purchased recently) and thought you might like to see the numbers.
>
> First I did a standard load test on all of them as determined in my Load
> Tester manual (3X the AH rating (330 Amps in this case) for 15 seconds)
> using the device below:
>
> http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html
>
> I then recharged each battery fully with my 12V smart charger
>
> http://www.battery-rechargeable-charger.com/vector-VEC1095A-car-battery-charger.htmlusing
> the AGM profile.
>
> I followed that by doing an AH capacity test using the procedure shown
> here:
>
> http://www.instructables.com/id/AmpHourTest/
>
> I bought a 400W inverter at Home Depot, bought an old plug in mechanical
> clock for $5 on Ebay, and used a 75W incandesent bulb which meant the load
> was at least 6.25 amps. I'm not sure how much current the old clock was
> drawing (probably not much). Even if the clock drew noticable current,
> that
> would mean a higher total draw and thus the AH results would be somewhat
> better than I found. But those AH values here are "at least" that much.
>
> You can argue with the specifics of these procedures - they may not be the
> most accurate way to do this, BUT the numbers are "RELATIVELY VALID" since
> I
> did the same thing to all the batteries both times.
>
> The batteries are 12V AGMs (110 AH rated)
> http://www.mrsolar.com/pdf/universal_battery/UB121100.pdf They are sealed
> so doing specific gravity testing of the acid is NOT possible and I
> understand that would only get me SOC anyway and not AH capacity.
>
> Here's what I found: .
>
> Group 1: Pack I was using - they were dying and I was starting to replace
> some, but I basically killed them by pushing them well below 20% several
> times (yes, David I committed battricide). I had to be towed home a couple
> of times and the last time my wife pushed my home the last mile with our
> Honda Civic. Have not driven the car since then. The very small AH
> numbers
> for this group don't really surprise me under the circumstances. The car
> sat
> for a week or so, but I had done a full charge of the pack as soon as I had
> gotten home. Then a few days before I did the testing I did a 3 hour
> equalization charge using my 120V Quick Charge Select-A-Charge (110V input;
> 10 Amp max). All were resting at about 13.2-13.3V each before the tests.
>
> Cycles on the battery Load test voltage AH capacity
> 60 ** 10.2V 33
> 60 ** 10.0V 16
> 120 10.6V 3
> 350 10.6V 3
> 120 10.7V 3
> 350 10.8V 5
> 60 ** 9.2V 4
> 350 9.6V 3
> 10 ** 9.8V 12
> 350 10.4V 3
>
>
> Group 2: Others (not yet used by me). I had charged them all about a week
> earlier one at a time using my 12V smart charger. They were resting about
> about 13.0-13.1V each. before the tests.
>
> Cycles on the battery Load test voltage AH capacity
> ** 9.0V 39
> ** 8.9V 53
> ** 9.4V 51
> ** 9.4V 47
> ** 9.6V 51
> ** 9.1V 54
> ** 9.2V 50
> ** 10.0V 57
> ** 9.6V 53
> ** 9.6V 53
> ** 8.8V 51
>
>
> ** had previously been used as part of a UPS standy system, but I really
> don't know how much use they've had (i.e., how hard they were pushed or how
> often they were cycled).
>
> It's hard to argue with these data. Bottom line is that CLEARLY THERE IS
> NO
> RELATIONSHIP BETWEEN THE TWO SETS OF FINDINGS. There doesn't seem to be
> much
> correlation between load test results and AH capacity testing. This may
> not
> be news to some of you but it was to me. I'm glad I went to the trouble and
> I now have the ability to test AH capacity.
>
> Given what we want to use the batteries for (deep cycling), and what I know
> about the history of these batteries, I'm much more inclined to trust the
> AH
> capacity numbers. My sense is that doing a conventional load test MAY tell
> you if a battery is really bad (it didn't here; all of the above voltages
> were a "pass" on the load tester), but it doesn't seem to really tell you
> if
> a deep cycle battery is any good for deep cycling.
>
> I now plan to install the 10 best of the "others" shortly (those with 47-57
> AH still in them) and see how they do.
>
>
> Peter Flipsen Jr
> Meridian, ID
> http://www.evalbum.com/1974
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