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

[Starlight Solar Power Systems]

Hi Lou,

On some of the Li battery brands that we sell, if the shunt current is +/- 1 Amp from zero, the current is not counted. On larger systems I have seen +/-2 Amps not counted. If the system spends much time there, counting error can accumulate. A battery can shut down on LV while the SoC meter still shows a high percentage. We have seen this several time from customers that don’t want to fully charge thinking they will make the Li battery last longer (damn internet blog myths). The solution is to fully charge regularly where the SoC counter is automatically reset when full charge parameters are met. 

If you can force the FNDC SoC to reset each time you full charge, it may provide better accuracy between your two counters. We often use Magnum Energy ME-BMK and it is always very close to the Li battery SoC because they both reset at full charge. 

Larry Crutcher
Starlight Solar Power Systems






On Aug 17, 2018, at 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 <mailto:lou at spreesolarsystems.com>
808 345 6762
Spree Solar Systems LLC 
CT-34322

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