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

[Chris Worcester]

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.com530-448-9692Sent 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






     
   	Jay
        July 
14, 2021 at 1:15 PM    
  Hi JeffIf it’s 
the energy cell xlc from Outback then it shows an eq requirement. If not that battery, most industrial
 quality VRLA  I’ve seen have a eq requirement, conditioning charge or 
something similar. And the lowering of capacity is 
common from experience. QuestionWhat equipment/brand  is charging it?JayPeltz power


  
     
   	Jeff Clearwater        July 
14, 2021 at 11:32 AM    
  

Thanks Dave - yes I've 
done whole pack load testing.  The deal with this pack though is that it
 is so remote and the expense of "just replace the pack" in terms of 
shipping and labor is extreme - (tiny Bahaman island with only regular 
small boat access}

And if it was toward the end of the pack's life anyway I'd not mess 
around - but with only 600 well documented cylces on a $25K pack - and 
with probably half that again in shipping and labor to replace - I'm 
needing to carefully document the lagging cells for either a warranty 
claim or at least to make good decisions going forward.

It's easy to access the cells as this is an EnergyCell AGM stack with 
easily accessible terminals and removable terminal bars.

If we replace we'd go LFP - on the order of 100 KWHrs.  So no small 
decision for the customer - so worth the testing.

Thanks!

Jeff Clearwater

Village Power Design

  www.villagepowerdesign.com









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