[RE-wrenches] How Best to Load Test 2 V Cells

[Jeff Clearwater]

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 <mailto:chris at solarwindworks.com>
> 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
> chris at solarwindworks.com
> 530-448-9692
>
> Sent from my Samsung Galaxy s9.
>
>
> -------- Original message --------
> From: Jeff Clearwater <jeffc at villagepowerdesign.com>
> Date: 7/14/21 1:42 PM (GMT-08:00)
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> 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 <mailto:jeffc at villagepowerdesign.com>
> 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
>
>
>
>
>
>
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