KS 84V charger, when is the voltage too high?

[null]

I just got a new (old 2019 stock, doh  ) 18XL. Will try to figure out if the battery pack is healthy.

In the meantime the charger seem to have too high voltage:

This is difficult to check because I can only measure it with no load and a crappy multimeter, and the 18XL internal reading won't show if it goes over 84,5V (worst idea ever). With a multimeter, no load, it shows 0,3V more than my recent charger. This in its turn already charges above 84,5V: when looking at the charging graph it doesn't slowly settle at 84,5, but reaches a ceiling while charger is pulling 45W at the wall. Already this I dont like, but that is the "better" / lower voltage charger.

The old stock one pulls over 100W when reaching the 84.5V report ceiling. After that I cant know just how high it will go, due to no reporting, and while the pull very slowly lowered, I disconnected it for fear of wearing ou the cells / overcharge.

So I plan to reduce the voltage of the worst charger, is there anything to target? I was thinking to try to have it settle on the wheels 84,5V internal reading.

Any suggestions otherwise? Is there any way of knowing what the actual battery voltage is? It seems downright dangerous to me to hide possible over voltage...

(The charge monitoring have been done on both the old stock 18XL and one that should be healthy. Pretty much same results.)

Thank you for any tips.

screenshot: Charge voltage not slowing down when reaching 84.5V..

Edited May 25, 2023 by null

[alcatraz]

Sounds to me like you want to avoid activating the overvoltage protection in the bms. 

It's quite impossible though because even if you have a charger set to 84.0000v you don't avoid the risk of overcharging. 

When (not if) cells get out of balance (even by a little), overvoltage protection is the only thing preventing the cells from being overcharged.

Personally I don't care if it's 84.3v or 85.1v etc, because when the first group reaches 4.2x v the bms will interrupt charging, fans will stop, and the light turns green. If the end voltage isn't 83-84v it means balancing is still working and so the charger needs to stay connected until balancing has completed.

[alcatraz]

Another problem of setting the charger to 84.000v is that under load it most likely can never reach that number. If the sag in the charger is relatively large (simple/low-end charger) then the project can backfire by the pack not reaching a desired end voltage for the balancing to complete properly.

[alcatraz]

I know there are many IFs here. I take comfort in my wheels by probing the packs and confirming that the groups indeed are balanced. Brand, mileage, age, doesn't really matter if the cells aren't balanced (which although unlikely, still can happen).

With balanced cells, you can actually ride/charge without a bms.

So it's extremely valuable to confirm that all the cells are balanced.

Being able to charge to 100% is the "poor man's" way to confirm that cells are balanced. But the assumption relies on the bms's overvoltage protection to be working, so it's not as reassuring as probing the pack.

[null]

Thank you for the care @alcatraz . I worded myself badly:
There is no reason to believe the battery pack is bad, we can put this question aside. Two other 18XL behave exactly the same. As its old stock I'll keep an eye on it, but without specific reason I won't pull it apart.

My first issue is that one stock KS charger is 0,3V higher than the other, and a whole 0,4V more than yet another KS stock charger I have.
The lowest voltage chargers CV phase curves out around 84,5V (on 3 different 18XL internal reading so they are probably not too off) that means the highest voltage one is possibly pushing 84,9V, all while being a new orignal stock charger with varnish to seal the potentiometer.

If the 84,5V "ceiling" of the EUC was the BMS over voltage protection that would be nice, but it isn't: the high voltage charger continues pulling 100W+ at the wall at that point (see previous curve) then lowers slowly, as per CV stage. Also the charge is there: I can ride several minutes before it shows less than 84,5V It just won't report the higher voltage..

So my second issue is that the KS18XL doesn't report numbers over 84,5V, no matter how much over voltage the pack has. Not displaying over voltage, especially when you ship stock chargers at 84,9V is a terrible idea IMO.

Conclusion: I have aligned the two highest voltage chargers to the lower one, which is still terminating charge at 84.5V but at least curves out there and dont go higher. The battery packs behave perfectly normally at this point. Had I not systematically monitored charging the high voltage charger would probably worn out the pack prematurely, or worse. I would suggest people with 18XLs to have a look.

edit: I'd love to have it even lower, but KS (at least 16S/18XL) have always had voltage on the higher side (Shottky diodes?) so I won't take any initiative that might make me miss out on balancing. If anyone have KS specific info I'm taker.
 

Edited May 31, 2023 by null

[alcatraz]

84.5v sounds good for the charger side.

A good practice is to monitor the pack end voltage in euc world, after each full charge. If something is off, you'll see the voltage drop.

[v8nice]

unfortunately the voltage displayed in the application is not necessarily the true voltage in the batteries. Recently I changed my XL motherboard (because of a voltage regulator problem headlight, fan, sound) this one always showed me 84.5v  at the end of the charge. I checked the batteries it was at 83.5v and the charger was at 84v.... With the new motherboard the voltage is correct, I raised the charger to 84.3v and the wheel is therefore charging  now at 84v real on the multimeter and in the application.