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

[Ray]

My experience has bee that all SOC meters can drift off over time.  Best 
I can figure is that they don't reset at full, or do reset when the 
battery is not fully charged.  This coupled with an inability to account 
for temperature variation and differences in discharge rates, can also 
contribute to inaccuracy.  Thus, my solution has been to not depend on 
auto starting the generator. The smartest control is the user 
themselves, who can look at the weather, look at their usage, time of 
day, SG of the batteries, voltage, etc. and better decide when to start 
the generator. Their batteries and generator last longer, and they spend 
$1000s less in propane over the life of the system.

For folks that insist on auto start, they better get ready for big fuel 
bills, generator replacement, and an overall less reliable system, since 
their is not human management of the system.  A seasoned off grid 
customer is always smarter than any auto start system.  That being said, 
the advent of batteries with their own BMS systems that can communicate 
with the rest of the system may make auto start a more viable and less 
costly option in the future

Ray Walters
Remote Solar
303 505-8760

On 8/18/18 7:24 AM, Tump wrote:
> Yep its is terrible! Spoke w/ a former member of their (OB)’s tech 
> support and was told that the counting of amp hours both up & down 
> drifts so you have to recalibrate monthly.
> This IS something OB is aware of and has no interest in addressing. 
> Thoughts…. remove and when you find a device that I am able to install 
> and get accurate info on multiple shunts to trigger gen start let me 
> know.T
>> On Aug 17, 2018, at 3:09 PM, Lou Russo <lou at spreesolarsystems.com 
>> <mailto: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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