Use a shunt in a lab with a white coat on! Not possible for me to do as I do not like shunts and connecting/disconnecting cells. I would just do the load test like Steve wrote and look for temp differences also. Since there are more than a few cells, it is time to get them ready for check writing. Remote places have to have very good bank accounts offgrid!
Dave Angelini Offgrid Solar "we go where powerlines don't" http://members.sti.net/offgridsolar/ [1] e-mail [email protected] [2] text 209 813 0060 On Wed, 14 Jul 2021 14:43:20 -0700, Jeff Clearwater wrote: Yes good thought Chris -I doubt if there is an IR tester anywhere on the island - but when I go I will for sure look at that - thanks for that. How would one measure battery resistance with voltage present? I guess with a known voltage applied and current held constant one could calculate? but then how do you know you are measuring resistance vs storing energy? I don't think that's possible - others? jc Chris Worcester [3] July 14, 2021 at 2:14 PM Has an infra-red thermometer been used on every battery's terminals to check for resistance? I recall, although this might be my own thoughts, that internal resistance of each cell can be measured with an ohm meter... Chris Worcester [email protected] [4] 530-448-9692 Sent from my Samsung Galaxy s9. -------- Original message -------- From: Jeff Clearwater [5] Date: 7/14/21 1:42 PM (GMT-08:00) To: RE-wrenches [6] Subject: Re: [RE-wrenches] How Best to Load Test 2 V Cells Hey Jay, Yes the Sunny island Master of this Quad SI AC-coupled off-grid system has been giving automatic Eq and Full charge charges perodically as appropriate to this 48 V EnergyCell RE2700 pack. We are getting whole pack volt drops way before we should at 600 well- maintained cycles. When we do whole pack testing - when the voltage drops off there are 5 of the 24 cells lagging - their voltage drops faster than the rest - but they operate well between 50%-100% - all busbars have been triple checked for corrosion and tourque. So it looks like they just aged prematurely - so I'm in the process of collating data from EnnexOS to get exact numbers on how they've been treated. But even with a few hard cycles they should held up better than they have. So perhaps a warranty claim - I've gone through charge settings with SMA etc. I did have the AHrs programmed slightly below rated AHrs due to confusion of whether the SI uses the 20 hr or 10 hr rate (in Europe they use 10 but apparently - unbeknowst to me - the US SI uses the 20 Hr - I swear SMA tech support years ago told me 10 hours) but now they are claiming that might be the culprit - I have a hard time believing that setting the Ahour rating in the SI to 2100 instead of 2288 as rated would lead to pack failure - but they are claiming that could have contributed. Thoughts? Best, Jeff Jeff Clearwater [7] July 14, 2021 at 1:42 PM Hey Jay, Yes the Sunny island Master of this Quad SI AC-coupled off-grid system has been giving automatic Eq and Full charge charges perodically as appropriate to this 48 V EnergyCell RE2700 pack. We are getting whole pack volt drops way before we should at 600 well- maintained cycles. When we do whole pack testing - when the voltage drops off there are 5 of the 24 cells lagging - their voltage drops faster than the rest - but they operate well between 50%-100% - all busbars have been triple checked for corrosion and tourque. So it looks like they just aged prematurely - so I'm in the process of collating data from EnnexOS to get exact numbers on how they've been treated. But even with a few hard cycles they should held up better than they have. So perhaps a warranty claim - I've gone through charge settings with SMA etc. I did have the AHrs programmed slightly below rated AHrs due to confusion of whether the SI uses the 20 hr or 10 hr rate (in Europe they use 10 but apparently - unbeknowst to me - the US SI uses the 20 Hr - I swear SMA tech support years ago told me 10 hours) but now they are claiming that might be the culprit - I have a hard time believing that setting the Ahour rating in the SI to 2100 instead of 2288 as rated would lead to pack failure - but they are claiming that could have contributed. Thoughts? Best, Jeff _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org [8] List Address: [email protected] [9] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org [10] There are two list archives for searching. 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