Today's Message Index:
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1. 07:18 PM - How to temperature derate AGM capacity? (Steve Stearns)
2. 08:44 PM - Re: How to temperature derate AGM capacity? (Robert L. Nuckolls, III)
Message 1
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| Subject: | How to temperature derate AGM capacity? |
Greetings All,
I build up and I'm using a 3 ohm version of Bob's Battery Capacity tester
that he designed a while back. So I get nominally a 4 Amp discharge which,
for a new 17 amp-hr AGM battery (whatever brand Batteries Plus is currently
selling), when new, I get something like 3:45 before the output voltage
drops below 11 volts (where my threshold is set). And after about 3 years,
it's capacity has dropped about 20% or more and I rotate it out (Longeze ->
Motorcycle -> Taylorcraft -> Telescope -> lab).
However, it's clear the tested capacity varies greatly with ambient
temperature so I would like to normalize my test results, based on
temperature, so I can get more accurate comparisons. Additionally, I'd
also like to understand the derating so that I can more accurately estimate
my effective no-alternator battery endurance given that I often fly up high
where it can be quite cold where the battery resides. So it's likely quite
a bit shorter than the time I measure in the lab at the same output
current. I Googled around and didn't find any answers.
Does anyone have the capacity derating for cold temps on an AGM battery
available?
Thanks,
Steve Stearns
O235 Longeze N45FC,
Taylorcraft BC12D
Message 2
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| Subject: | Re: How to temperature derate AGM capacity? |
At 09:17 PM 8/21/2021, you wrote:
>Greetings All,
>
>I build up and I'm using a 3 ohm version of
>Bob's Battery Capacity tester that he designed a
>while back.=C2 So I get nominally a 4 Amp
>discharge which, for a new 17 amp-hr AGM battery
>(whatever brand Batteries Plus is currently
>selling), when new, I get something=C2 like 3:45
>before the output voltage drops below 11 volts
>(where my threshold is set).=C2 And after about 3
>years, it's capacity has dropped about 20% or
>more and I rotate it out (Longeze -> Motorcycle
>-> Taylorcraft -> Telescope -> lab).
>
>However, it's clear the tested capacity varies
>greatly with ambient temperature so I would like
>to normalize my test results, based on
>temperature, so I can get more accurate
>comparisons.=C2 Additionally, I'd also like to
>understand the derating so that I can more
>accurately=C2 estimate my effective no-alternator
>battery endurance given that I often fly up high
>where it can be quite cold where the battery
>resides.=C2 So it's likely quite a bit shorter
>than the time I measure in the lab at the same
>output current.=C2 I Googled around and didn't find any answers.
>
>Does anyone have the capacity derating for cold
>temps on an AGM battery available?
See Figure 5 of https://tinyurl.com/yekn362u
Figure 6 of
https://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf
https://kb.unavco.org/kb/article/sla-battery-cold-performance-tests-gel-vs-
agm-386.html
https://www.dcbattery.com/lifeline_capacity_temp_graph.html
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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