Strange problem cell nr. 9 always low

Hahaha sorry :oops:

The story in short.

Troubleshoot 1.
Bike had a lot of cut off problems.
By troubleshooting I have found cell nr. 9 is always low voltage after a ride.
When charging ( with e bike charger) the cell will never get full capacity.
I am still able to charge (with rc charger) the cell and capacity in is +/- 4,5 Ah.
So the cell nr. 9 is never full after charging with e bike charger.

Troubleshoot 2.
I have replaced cell nr.9 many times with new cells.
But the problem still exist.
So I rode the bike without bms and all cells volatges were close to each other.
And when charging cells separate all capacity in were close to each other.

Troubeshoot 3.
I rode the bike with bms connected again.
And the problem came back; cell nr. 9 is low voltage and never fully charged.
So I replaced the bms and cell nr. 9 problem is gone :D
When chargring with e bike charger cell nr. 9 is now full.

Troubleshoot 4.
The new bms is not working right cell nr. 1 is always low voltage when charging will never get to 3.6V.
So did some troubleshooting (thanks Dnmum) and I have found cell nr. 1 mosfet is shorted.
So cell nr. 1 is always discharging through the bms discharging resistors.
After replacing the cell nr. 1 mosfet.
Problem is gone no more cell nr. 1 discharging.
Cell nr. 1 votages is now close to other cells when charging to the end total cut off voltage.

Sorry for my bad English I am a Dutch man :oops:

Thanks for hel all! 8)
 
Yup two bad bms :evil:

But I have bought a new one for spare.
Because of my battery design, I have to use this bms again.
Otherwise I have change cable routing..... :evil:

17s26s-24a-max-discharge-current-bms.jpg
 
usually the reason the shunt transistors fail is when the BMS is shorted to the battery and the current through the shunt transistor or the voltage across it is enuff to burn up the mosfet.

this happens a lot on split packs where there is a loose connection between the two portions of the battery on the main power leads. the loose connection causes the current to flow through the shunt transistor instead of the large conductor and that burns up the shunt transistor. this is why i am always warning people to use a solid, soldered connection on the wire between the two halves.

this is the BMS battery BMS i think. it appears to use 3.65V as the balancing voltage.

that used to be the balancing voltage used on all the BMSs but now they use 3.60V for the balancing voltage on most newer designs since the full charge voltage of 3.65V allows plating to occur when the cell voltage climbs above 3.60V even though 3.65V is considered fully charged.

the old headway BMS uses 3.65V for the balancing voltage. the bestechpower D131 i use is set to 3.60V for the balancing.
 
Yup it is bmsbattery bms.

Thanks for your info! 8)

So you mean the bms will cut off the charger when voltage is above 3.6V.
And the bms will balancing the cells when voltage is 3.6V?

I hope I will get a new version of bms.
Otherwise I have to make a decission to modify bms battery cable routing and use newer versions bms's 8)
 
the BMS will turn off the charging mosfets when any cell reaches the 3.90V HVC high voltage cutoff. it will allow the shunt transistor to keep draining the charge off until the voltage of that cell drops back to the reset voltage which is usually 3.8V and then the mosfets are turned on again.

the balancing is different and the shunt balancing transistors turn on when the voltage on their channel climbs above 3.65V for your BMS. that is when the current from the charger flows around the cell, but since the limit for how much current that flows around the cell is limited by the shunt resistor, then the voltage on the cell can continue rising until it hits the HVC, unless the pack has charged up enuff that the cell cann no longer reach the 3.9V level so it continues bypassing current from the charger until the entire series of cells is now balancing.

it was never clear if your #9 shunt transistor on the first BMS was itself defective since that was never tested. that was what i was talking about initially. you had decided it was bad, but had not proven it.

you can test the shunt transistor easily using the diode tester function of the voltmeter. except that they are p channel mosfets used for the shunt transistor so the forward bias of the body diode is from drain to source.
 
dogman said:
......To e-beach, how do those cells hold up after overnight off the charger? Or just 2 hours later. That's when you'd know if one was self discharging a lot.
Click to expand...

OK, to follow-up.

16 hours on the charger.....31 hours of letting my bike sit to see what the bms would do....

After of 31 hours of sitting, the cells read like this:

1: 3.59 7: 3.58
2: 3.57 8: 3.58
3: 3.60 9: 3.58
4: 3.58 10: 3.58
5: 3.57 11: 3.58
6: 3.58 12: 3.58

Not too bad I would say....

:D
 
e-beach said:
dogman said:
......To e-beach, how do those cells hold up after overnight off the charger? Or just 2 hours later. That's when you'd know if one was self discharging a lot.
Click to expand...

OK, to follow-up.

16 hours on the charger.....31 hours of letting my bike sit to see what the bms would do....

After of 31 hours of sitting, the cells read like this:

1: 3.59_____7: 3.58
2: 3.57_____8: 3.58
3: 3.60_____9: 3.58
4: 3.58_____10: 3.58
5: 3.57_____11: 3.58
6: 3.58_____12: 3.58

Not too bad I would say....

:D
Click to expand...
 
Thank you:)

Yeah it's potted in the black goop.

And as mentioned before I have destroy this bms, while taking off a good mosfet for repairing the new bms cell nr. 1 problem.
But i have bought a spare one now.

Also I set the charger volatge to 57.6V (read from my bms info description).
But cell nr. 1 is still the first who reach 3.8 - 3.9 volt.
While other are about 3.5 - 3.6 volt.

When balancing rc charger all cells are most the same voltages.

I think I have to live with this problem :D
Hopefully the pack will last another year and I am content with it lifespan (in total of 2.5 year) 8)
 
when one of the cells climbs faster in voltage from the same full discharged level then it is usually because the capacity of that cell to store charge has been reduced.

capacity is the variable that has to be balanced.
 
Small different between 3.6v and 3.9v but they at top of charge rating and 3.5v is full. But 3.8v and over is high after an hour 3.5 or 3.45 is full. For use or 3.4v. Is good for full.
 
Thanks for replies! 8)

I have set charging voltage to 57.6V and when pack is full (charger cut off).
Most cells volatges are 3.5-3.6V.
When pack is continuous connected cell nr. 1 volatges wull rise up to 3.7V.

Pack is now working, thanks all! :D
 
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