Inconsistent voltage reported from BMS

[NorthTown2022]

So, It appears I am having inconsistent voltages being reported by the BMS. It's a JBD AP20S003S contactor model.

The voltages at rest, measured at the cells measure exactly the same at the BMS connector to .000v while the BMS reads 6 to 11mv above the DVOM. This was measured at 98% SOC (which is not entirely accurate).

Discharging at 56A 95% SOC and BMS reporting 3.28 - 3.29v the BMS reads -1mv to 6mv above DVOM.
Discharging at 56A 90.8% SOC and BMS reporting 3.28 - 3.29v the BMS reads -2mv to 5mv above DVOM.

Charging at 25A 91% SOC and BMS reporting 3.36 - 3.36v the BMS reads 9mv to 12mv above DVOM.
Charging at 49A 92.9% SOC and BMS reporting 3.38 - 3.39v the BMS reads 9mv to 12mv above DVOM.
Charging at 60A 94.8% SOC and BMS reporting 3.37 - 3.38v the BMS reads 10mv to 17mv above DVOM.
Charging at 25A 96% SOC and BMS reporting 3.37 - 3.38v the BMS reads 8mv to 12mv above DVOM.

@John Frum

 

[sunshine_eggo]

LOL... I had no idea you were dealing in XXmV.

To be clear, you observe no deviation > 0.02V?

IMHO, you're lucky they are as good as they are!!!!

You likely missed it, but my Batrium varied by ±5mV from my Fluke at rest.

I see nothing wrong here.

SoC isnt' accurate until it's synced at 100%

 

[John Frum]

So, It appears I am having inconsistent voltages being reported by the BMS. It's a JBD AP20S003S contactor model.

The voltages at rest, measured at the cells measure exactly the same at the BMS connector to .000v while the BMS reads 6 to 11mv above the DVOM. This was measured at 98% SOC (which is not entirely accurate).

Since the pack has not yet been cycled I don't trust the soc.

Discharging at 56A 95% SOC and BMS reporting 3.28 - 3.29v the BMS reads -1mv to 6mv above DVOM.
Discharging at 56A 90.8% SOC and BMS reporting 3.28 - 3.29v the BMS reads -2mv to 5mv above DVOM.

Charging at 25A 91% SOC and BMS reporting 3.36 - 3.36v the BMS reads 9mv to 12mv above DVOM.
Charging at 49A 92.9% SOC and BMS reporting 3.38 - 3.39v the BMS reads 9mv to 12mv above DVOM.
Charging at 60A 94.8% SOC and BMS reporting 3.37 - 3.38v the BMS reads 10mv to 17mv above DVOM.
Charging at 25A 96% SOC and BMS reporting 3.37 - 3.38v the BMS reads 8mv to 12mv above DVOM.

Was balancing enabled during any of the tests?
Did you do the tests in the order of the reported results?
If yes, I wonder if drift is increasing over time.
Possibly due to something getting warmer from the tests.

Anyway its ok for a BMS to have an offset from your reference meter but a drifting offset is bad.
I don't trust this BMS to protect your cells.
Plus it has other issues as in....
Temp sensors are quite inaccurate.
balance can not be limited to charge only.

 

[John Frum]

LOL... I had no idea you were dealing in XXmV.

To be clear, you observe no deviation > 0.02V?

IMHO, you're lucky they are as good as they are!!!!

You likely missed it, but my Batrium varied by ±5mV from my Fluke at rest.

I see nothing wrong here.

My bms is a consistent +.003V per cell relative to my reference meter.
I wouldn't be concerned if it was +-.02V per cell as long as it was consistent.

 

[sunshine_eggo]

My bms is a consistent +.003V per cell relative to my reference meter.
I wouldn't be concerned if it was +-.02V per cell as long as it was consistent.

You're just luckier.

IMHO, cheap Chinese stuff @ 0.XXNV. N = noise level.

 

[NorthTown2022]

Since the pack has not yet been cycled I don't trust the soc.

Was balancing enabled during any of the tests?

no

Did you do the tests in the order of the reported results?

Yes

If yes, I wonder if drift is increasing over time.

Seems to be load..

Possibly due to something getting warmer from the tests.

Anyway its ok for a BMS to have an offset from your reference meter but a drifting offset is bad.
I don't trust this BMS to protect your cells.
Plus it has other issues as in....
Temp sensors are quite inaccurate.

Now that I know there is an internal sensor, I believe the display shows the most critical value. I tested the external sensor and it is working fine.. just need to click on the temp button

balance can not be limited to charge only.

This is still a problem

 

[NorthTown2022]

LOL... I had no idea you were dealing in XXmV.

To be clear, you observe no deviation > 0.02V?

IMHO, you're lucky they are as good as they are!!!!

I still like the sound of the supervisor and K9

You likely missed it, but my Batrium varied by ±5mV from my Fluke at rest.

I see nothing wrong here.

SoC isnt' accurate until it's synced at 100%

I'm learning!

 

[John Frum]

You're just luckier.

IMHO, cheap Chinese stuff @ 0.XXNV. N = noise level.

Well, now I will feel foolish is @NorthTown2022 gets another bms and its similarly in terms of drift.
But I have to call it like I see it.

Seems to be load..

Load means discharge.
I see from your report that the drift is higher with charge current and lower with discharge current.
What do you mean by load?

Now that I know there is an internal sensor, I believe the display shows the most critical value. I tested the external sensor and it is working fine.. just need to click on the temp button

I must have missed something.
Yesterday you confirmed the sensor on the cell was 8C out.
Were you actually talking about a temperature sensor within the BMS itself?

 

[NorthTown2022]

Well, now I will feel foolish is @NorthTown2022 gets another bms and its similarly in terms of drift.
But I have to call it like I see it.


Load means discharge.
I see from your report that the drift is higher with charge current and lower with discharge current.
What do you mean by load?

Ok, I meant charge current not load.

I must have missed something.
Yesterday you confirmed the sensor on the cell was 8C out.

Yesterday I thought there was only one temp sensor, its easily calibrated by clicking on it. @HRTKD and @WingNut helped me out with this.

Were you actually talking about a temperature sensor within the BMS itself?

Yes. I don't see anything about it in the manual though.. just external yet It looks like I may actually have one external and two internal sensors yet to be confirmed.

So the big issue now seems to be balance while charging..

 

[John Frum]

Having a second to digest the report...

Where exactly are you putting the dvom probes on the terminals during these tests?
I suggest the spare connection point on the terminal block.

 

[John Frum]

So the big issue now seems to be balance while charging..

Yes and that is not a deal breaker.
Just set the trigger and release thresholds a little higher and it be ok.

If you are ok with the voltage sense drift I'll not mention it again.

 

[NorthTown2022]

Having a second to digest the report...

Where exactly are you putting the dvom probes on the terminals during these tests?
I suggest the spare connection point on the terminal block.

Right on the cell terminals. Are you suggesting I may get a different reading at the terminal block? It may change some there while charging or discharging but 100% for sure I got the exact same results at rest from the BMS plug.

 

[NorthTown2022]

Yes and that is not a deal breaker.
Just set the trigger and release thresholds a little higher and it be ok.

I think the only parameter is balance turn on voltage.

If you are ok with the voltage sense drift I'll not mention it again.

Hehe.. maybe just until I get everything setup and have a chance to recuperate from all my spending so I can upgrade to something that speaks vic

 

[John Frum]

I'm confused ^

 

[John Frum]

Right on the cell terminals. Are you suggesting I may get a different reading at the terminal block?

Yes.
I expect the pattern will be tighter.

 

[NorthTown2022]

I'm confused ^

I hit post before typing by accident..

 

[John Frum]

@sunshine_eggo what is the temperature envelope for your cells?
Mine live between 24C and 29C.

 

[sunshine_eggo]

@sunshine_eggo what is the temperature envelope for your cells?
Mine live between 24C and 29C.

-12 to 43°C

 

[Ampster]

Right on the cell terminals. Are you suggesting I may get a different reading at the terminal block?

Not but measuring it from the top of a stainless steel bolt would be different. Are your cell terminals not covered by bus bars like mine. I have to slide in from the side or use the bus bar as the measuring point. That is where my BMS picks up the voltage. My BMS is connected to a mid point on the bus bar and when using my voltmeter I try to use that point to verify,

 

[sunshine_eggo]

In my experience, if measuring OCV at the screws/nuts/busbar/whatever vs. the terminal face makes a difference in voltage reading, something is horribly wrong.

Aluminum terminal faces are the worst. Al rapidly oxidizes and forms a resistive coating. On my 28 23" Al bus bars for the NMC battery, I aggressively buffed them with scotchbrite and immeditely applied NO-OX-ID "A-Special" to the terminal contact surface. Anywhere I attached a sensing lead or other terminal on top of the bus bar, I scrubbed that spot with a stainless wire brush and applied the NO-OX between the sense lead and the bus bar. It took me about 4 hours just to make all the connections and torque 588 nuts...