Wrong percentage JBD/Overkill

[42OhmsPA]

I just measured the JBD SP16S020 V1.1 at .015A @ 26.4V so idle power draw with bluetooth dongle running is about 0.4 watts. After 60 seconds of no activity (no charging, discharging and with BT ap closed) it shuts and goes below anything I can measure with DC clamp. Even if the ap.is running in the background of my phone the Bluetooth remains active.

I just found the calibration section in the Overkill BMS ap but haven't messed with it yet. My clamp meter always reads about 5% low so I'll have to try that with actual inline Fluke ammeter. It will be interesting if there is a way to improve it's low power draw sensing I'm sure that is the main cause of drift. From what I have seen the charge and discharge readings seem accurate from JBD.

@42OhmsPA Im trying the 100% at 3.35 to try and get a more accurate reset when resting and that should be easy to dial in (99.5% resting basically).

I noticed the the generic lifepo4 normal and lifepo4 lite 20% 40% 60% 80% voltage settings are way off compared what JBD set from the factory. This is a screenshot of the custom settings JBD sent me, which is much more accurate and precise. If we can get a general consensus on these numbers we will have a much better chance of gauging SOC at any time with a quick rest.

Thank you very much for those values. I'll try entering them tomorrow.

I attached some crappy photos of the current settings I'm running.

 

[bronxfire]

actually the SCC has the job to manage the battery, the BMS is there to protect the cells if the SCC doesn't, or one single cell gets too high/lowells get too hot/cold / but the SCC doesn't know this information, it only knows the total pack/ESS voltage.
I had some issues with my batteries and SOC until I bought the Victron 500A smart shunt, then my life changed.

Agreed
But i just thought a product whose sole function was to manage a battery would always know whats happening in the battery. Maybe i expect too much

 

[SupraSPL]

I doubt there is any way to improve the threshold required to trigger power draw ..... I had the same problem with my Chargery BMS.
I haven't experimented enough with the JK BMS to figure out how much low of current it draw it will detect.
I think the higher the amperage the BMS will handle, the less sensitive it is going to be for low current draw situations ..... also don't know how low of current the Victron shunts will measure ... but, they are probably better.

One hack I am experimenting with is increasing the setting for "self-discharge". Since the problem seems to be on the discharge side, that might allow us to dial it in much closer. Stock settings I have seen are 0.1% and 2% (per day) so I'm going to try 1% and 2%.

 

[SupraSPL]

Thank you very much for those values. I'll try entering them tomorrow.

I attached some crappy photos of the current settings I'm running.

Those look pretty good. I noticed that JBD set 100% at 3.417 and I might switch mine to that since the battery would be pretty full before reaching that and it's not high enough to distort the 100% resting voltage by much.

 

[OffGridForGood]

Agreed
But i just thought a product whose sole function was to manage a battery would always know whats happening in the battery. Maybe i expect too much

I don't disagree, however the BMS is mostly set up to be a switch - turn off charge or discharge if total current exceeds "x" , a cell temp or voltage is more or less than "y" & "z" - and to manage cell balancing function.
I don't know if a typical JK BMS has a built in 'shunt' - it may have, however it seems none of the BMS's in this price range track the pack SOC very well for very long.

 

[time2roll]

Please pay attention to its ability to sense discharge under 30 watts. Mine and many others dont sense any discharge under that amount of draw. So in theory if u only draw 25 watts for 2 weeks straight it would be 8400watts depleted and this stupid bms would still think 100%??. Its sole purpose is to manage battery and ita not accurate. Sorry im not satisfied with this bms

The stupid BMS has voltage settings programmed by the smart user to keep the state of charge reasonably on track.

Otherwise put a half amp load on and see if it still says 100% as it drops to 3.0 vpc.

 

[JerzyR]

Thanks a lot everyone! Now I have much better image of what is going on in my battery pack.
I've entered values suggested by @SupraSPL

Do you guys use external coloumb meters? I use my van also in winter for skiing in places that doesn't get much sun and nowing how much is left my battery is vital. So I'm wondering if I can relay on my BMS readings or not.

Now I have to wait for a sunny day - I charge from solar panels and engine alternator - and check how high it will go. I suspect that yesterday it didn't charge all the way because van was in a shadow for a while.

 

[bronxfire]

The stupid BMS has voltage settings programmed by the smart user to keep the state of charge reasonably on track.

Otherwise put a half amp load on and see if it still says 100% as it drops to 3.0 vpc.

i dont think you read what i was saying. i shouldnt have to program it to see if 1.5 amps are coming through the bms. it doesnt see it so it reports zero discharge current when in fact 1.5 amps are being drawn. even after i calibrated it.

 

[time2roll]

i dont think you read what i was saying. i shouldnt have to program it to see if 1.5 amps are coming through the bms. it doesnt see it so it reports zero discharge current when in fact 1.5 amps are being drawn. even after i calibrated it.

I am just saying in all practical use the very small draw has little effect.

 

[bronxfire]

I am just saying in all practical use the very small draw has little effect.

actually what u were saying was i was stupid but i figured i wouldnt respond with a nasty reply because i dont know you. just stating what ive noticed

 

[42OhmsPA]

Play nicely boys and girls....
Here's a great example of how they don't read low currents. I wish I were home to see what the shunt is reading...

 

[bronxfire]

Play nicely boys and girls....
Here's a great example of how they don't read low currents. I wish I were home to see what the shunt is reading...
View attachment 186647View attachment 186648

pack 2 shows no draw. i see that

 

[time2roll]

actually what u were saying was i was stupid but i figured i wouldnt respond with a nasty reply because i dont know you. just stating what ive noticed

'stupid BMS' were your words I repeated. No insult intended.

 

[Brett V]

Thanks. That could be a pain with multiple packs. Added to the project list.

Would that be on page 2 or 3?

 

[SupraSPL]

The way I read it he was calling the smart BMS stupid and the user smart, because we have to feed it custom voltage numbers to keep it in line, which is true but it's a minor issue overall if we can mostly fix it with the self discharge setting