---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Sat 08/21/21: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 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 _____________________________________ Time: 07:18:38 PM PST US From: Steve Stearns Subject: AeroElectric-List: 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 _____________________________________ Time: 08:44:19 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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?" ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.