[RE-wrenches] SOC, FNDC, and LFP batteries

[Jay]

Interesting thread as I was just in contact with someone with a LGchem coupled to a solar edge inverter. 
He’s seeing at times 20-25% less capacity than rated kWh and pretty much never actual capacity. Tech support gives some wishy washy answers as to why this would be. Where is the difference, is it in the communication between units or the BMS?  And funny as he’s never seeing more capacity. 

Maybe there are some inaccuracies in the BMS’s? 

Standard OB, trimetric and midnight wiz bang meters all require frequent meeting of charge parameters ( volt/amps) to keep the devices accurate.  I’ve got 4 meters that I compare and if they are full daily it’s about 1-2% difference between them. If it’s been 7-10 days since full, then they could be off by 10-15%+ off. 

Curious what others are seeing

Jay

Peltz power. 





> On Aug 18, 2018, at 9:40 AM, Jerry Shafer <jerrysgarage01 at gmail.com> wrote:
> 
> Lou
> Sounds like you are having the same issue we did, l adjusted the size of the battery down to 50% of the battery rating and so far the values appear to follow in. We will also be installing a DC  CT on the egauge to see and have a better idea of whats going and out outside of the BMU
> Jerry
> 
>> On Fri, Aug 17, 2018, 12:09 PM Lou Russo <lou at spreesolarsystems.com> wrote:
>> Hello All,
>> 
>> Does anybody have any insight in getting the SOC to report accurately on the Outback FNDC when using batteries that have a minimal voltage curve? I have several systems with LFP batteries that have both a eGauge (communicating directly with the battery BMU) and a FNDC and I get wildly different SOCs. In a typical  24 hour period (12am-12am) I get SOCs on the FNDC that vary 2% to 34% of what the battery BMUs are reporting. I am assuming that the BMUs are reporting accurately. I would think a 1%-5% difference would be acceptable.
>> 
>> Any help or thoughts on this subject  would be greatly appreciated.  
>> 
>> Aloha,
>> 
>> Lou Russo
>> lou at spreesolarsystems.com
>> 808 345 6762
>> Spree Solar Systems LLC 
>> CT-34322
>> 
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