Overkill BMS onboard shunt accurate?

[james1]

Just put 16s into service with 100 ah Overkill Bms.
Did a 6 minute test with constant draw no PV input. Watched the onboard bms shunt system display (x ah of 280 ah) then shut off load and started PV input. The drawdown matched the fill-up.
So it seems accurate at that tiny test window.

Anyone here with actual experience with the Overkill over a larger drawdown and over several months monitoring it compared to an external shunt?

 

[james1]

Just put 16s into service with 100 ah Overkill Bms.
Did a 6 minute test with constant draw no PV input. Watched the onboard bms shunt system display (x ah of 280 ah) then shut off load and started PV input. The drawdown matched the fill-up.
So it seems accurate at that tiny test window.

Anyone here with actual experience with the Overkill over a larger drawdown and over several months monitoring it compared to an external shunt?

My test was 1650 watt constant draw for 6 minutes then refill at 1100 watts(Max solar at the moment)

 

[alcook62]

My test was 1650 watt constant draw for 6 minutes then refill at 1100 watts(Max solar at the moment)

I haven't done an actual test, but anecdotal evidence comparing the soc between the Whizbang Jr. shunt and my Overkill BMS they are within one percent of each other. Normally, it is spot on.
Anyways, the Overkill BMS doesn't track the soc via a shunt. I believe it's by coulomb counting.

 

[TacomaJoe]

I ran my bank down and turned on the charging overnight. This morning my AiLi shunt shows 766.4Ah and my LIONTRON app shows 766.82Ah (which does in fact equal the sum of the Ah reported by the 3 BMSs). In my trailer I have about a 1A parasitic draw and I do see drift between the shunt reading and the BMS reading, but during normal usage and higher charge/discharge currents the readings line up.

 

[PreppenWolf]

I have (8) of these BMSs and they are pretty accurate for live draws, but your SOC/Ah long term tracking will be trash. You have to hit the reset button in the app to get the Ah to refresh to proper values because the BMS is tracking voltage and extrapolating Ah, which it doesn't refresh in its own. It takes the value at reset and then the value will drift downward over time.

Use a real, separate shunt if you want Ah tracking. I just use voltage, so it doesn't bother me.