Overkill bms useless

[time2roll]

I run both in parallel and the drift is always about 7-12% off. Someone mentioned that JDB might use the voltage values in the config vs true measurements. Starting to think that individual is correct.

How deep are the cycles?

 

[ChrisG]

How deep are the cycles?

Not many, about 120 total cycles and from 85-15%

 

[upnorthandpersonal]

Out of curiosity, does anyone know if the JK or Seplos BMS actually track current accurately?

No, not really. You can calibrate the JK, but it won't be as accurate as a dedicated shunt. Personally, I want my BMS just to protect the cells, not report the state of charge or anything else. I can use a shunt for that - I just want the BMS to turn it all off if something bad happens, and both the JK and the JBD/Overkill work perfectly fine for this.

 

[SeaGal]

Not many, about 120 total cycles and from 85-15%

You need to get it up to 100% from time to time to keep the SOC in sync. Going from 15 to 85 is always going to drift as the BMS is not hitting any reference point.

 

[ChrisG]

You need to get it up to 100% from time to time to keep the SOC in sync. Going from 15 to 85 is always going to drift as the BMS is not hitting any reference point.

I do every 3 days, always gets to 100 to balance over 3.45v. Cells always tight:

 

[time2roll]

Would be interesting to go to 0% shut down and see what calls it closer.

 

[ChrisG]

I do every 3 days, always gets to 100 to balance over 3.45v. Cells always tight:

Not to far off right now. 59%vs65%.

 

[time2roll]

Does the app show in 5% increments?

 

[ChrisG]

Does the app show in 5% increments?

Nope. 1%.

 

[ChrisG]

Would be interesting to go to 0% shut down and see what calls it closer.

The JBD gets to 0% MUCH faster than Victron.

 

[time2roll]

The JBD gets to 0% MUCH faster than Victron.

So JBD says zero before it actually shuts down?
Does this somewhat match the cell capacity voltages programmed?

 

[ChrisG]

So JBD says zero before it actually shuts down?
Does this somewhat match the cell capacity voltages programmed?

Did a full charge to 56v, 100%, let it balance for about an hour above 3.45v. JDB hits 0% SOC, Victron Shut at 11% SOC. Victron is correct on SOC and AH still available.

 

[42OhmsPA]

...

 

[ChrisG]

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So JDB is reporting 82% but shunt is saying 100%? That’s quite a gap.

 

[42OhmsPA]

So JDB is reporting 82% but shunt is saying 100%? That’s quite a gap.

Yes but I have the shunt set to 742ah capacity vs the 765ah from the BMSs. Still it's quite the gap.
The issue, I think, is this time of year I'm lucky to break even with loads vs PV for a majority of the day(s)... BMS gets all out of whack because it doesn't see a full charge and has very low current for long periods of time.

 

[time2roll]

Wait now. The battery has not been at full charge for a while but the shunt says 100%?

 

[42OhmsPA]

Wait now. The battery has not been at full charge for a while but the shunt says 100%?

Correct.



I reset the shunt to match the BMS and set grid charging to 10a, 3 JBDs in parallel don't see the 10a.


I should just buy a bloody blue smart shunt, I need a new MPPT maybe that'll be blue too.

 

[RCinFLA]

Cheap bms's generally do not do anything to compensate for op amp DC offset. With the amplification from shunt resistance voltage the offset can represent +/- 1 to 3 amps of uncertainty. Most cheap BMS's just set a threshold below which they just declare it to be zero current.

Quality shunts like Victron employ DC offset correction.

 

[Quattrohead]

Here is a smart shunt for you.

50v oh shit
51v better tell her indoors no washing
52v I wish the sun would shine
53v good but I want more
54v niceeee
55v they getting warm
56v stoppppp

 

[42OhmsPA]

Already have a difference between the shunt and BMS. Wow that balance is embarrassing. (the 305s were not top balanced)