Short 103v voltage spike on a 20s battery after charging

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Jul 29, 2019
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14
So my battery sometimes only charges up to 82.5v, but after I disconnect the charger and twist the throttle for a sec (motor spin in air)voltage goes up to 83.5v and stays there, it also cuts off the motor until i re-twist the throttle again, but the nucular controller/display doesn't shut down

today for the first time the voltage (on controller's display) spiked to 103v for 1 second for several quick voltage twists, after each voltage spike the battery/controller cut off the motor until I re-twist the throttle. The voltage went back to 83v each time

It's a two year old bike and I never had a 84.5< voltage!

Is it possible that some cells got charged up to 5-7 volts?!

Should I dump the battery?
 
The battery voltage isn't increasing when you discharge it. I expect that electrical noise is spoofing your voltmeter.

If your controller is set to regeneratively brake, turn that feature off and see if it doesn't fix the problem.
 
Lh100Error10 said:
It's a two year old bike and I never had a 84.5< voltage!
Should we assume it's a 20S lithium ion battery pack, or something else?

If so,
1. what is the output voltage of your charger?
2. does your battery have a BMS?
3. has the battery ever been balanced in the last 2 years?
 
Chalo said:
The battery voltage isn't increasing when you discharge it. I expect that electrical noise is spoofing your voltmeter.

If your controller is set to regeneratively brake, turn that feature off and see if it doesn't fix the problem.

Regen is off


E-HP said:
Lh100Error10 said:
It's a two year old bike and I never had a 84.5< voltage!
Should we assume it's a 20S lithium ion battery pack, or something else?

If so,
1. what is the output voltage of your charger?
2. does your battery have a BMS?
3. has the battery ever been balanced in the last 2 years?
20s battery yes.
1.My charger voltage is officially 84v but 2 voltage meters show it's about 84.5
2.yes
3. No
 
Lh100Error10 said:
20s battery yes.
1.My charger voltage is officially 84v but 2 voltage meters show it's about 84.5
2.yes
3. No

The charger should be adjusted to 84V, then keep the battery on the charger overnight or more, if it's never been balanced.
 
E-HP said:
Lh100Error10 said:
20s battery yes.
1.My charger voltage is officially 84v but 2 voltage meters show it's about 84.5
2.yes
3. No

The charger should be adjusted to 84V, then keep the battery on the charger overnight or more, if it's never been balanced.

How many hours do you think it takes to balance once fully charged? I’ve done that method you’re suggesting by just leaving the charger plugged in all night.
 
E-HP said:
Lh100Error10 said:
20s battery yes.
1.My charger voltage is officially 84v but 2 voltage meters show it's about 84.5
2.yes
3. No

The charger should be adjusted to 84V, then keep the battery on the charger overnight or more, if it's never been balanced.


How can you explain the voltage in this video? it was taken right after disconnecting the charge that turned green(82.7v)

https://www.veed.io/view/0d94df76-1791-4ca0-b241-2021e4bd6cac
 
I already told you it's probably electrical noise. When you apply a pulse width modulated AC load like a motor controller to a battery, the voltage will exhibit a ripple. This makes it more difficult for the voltmeter to decide the true voltage. Whatever algorithm is used to determine the DC voltage of a rippled signal might come up with something higher than the battery's resting voltage, but incorrect.
 
Chalo said:
I already told you it's probably electrical noise. When you apply a pulse width modulated AC load like a motor controller to a battery, the voltage will exhibit a ripple. This makes it more difficult for the voltmeter to decide the true voltage. Whatever algorithm is used to determine the DC voltage of a rippled signal might come up with something higher than the battery's resting voltage, but incorrect.
Does it also explain the small permanent increase in voltage from 82.7v to 83.2v? In the video it wasn't just a spike

Thanks I appreciate it :thumb: :bigthumb:
 
Lh100Error10 said:
Chalo said:
I already told you it's probably electrical noise. When you apply a pulse width modulated AC load like a motor controller to a battery, the voltage will exhibit a ripple. This makes it more difficult for the voltmeter to decide the true voltage. Whatever algorithm is used to determine the DC voltage of a rippled signal might come up with something higher than the battery's resting voltage, but incorrect.
Does it also explain the small permanent increase in voltage from 82.7v to 83.2v? In the video it wasn't just a spike

Thanks I appreciate it :thumb: :bigthumb:

If it's some kind of error correction or smoothing, then the display will drift back down after a moment of no motor activity. Does it?
 
Chalo said:
Lh100Error10 said:
Chalo said:
I already told you it's probably electrical noise. When you apply a pulse width modulated AC load like a motor controller to a battery, the voltage will exhibit a ripple. This makes it more difficult for the voltmeter to decide the true voltage. Whatever algorithm is used to determine the DC voltage of a rippled signal might come up with something higher than the battery's resting voltage, but incorrect.
Does it also explain the small permanent increase in voltage from 82.7v to 83.2v? In the video it wasn't just a spike

Thanks I appreciate it :thumb: :bigthumb:

If it's some kind of error correction or smoothing, then the display will drift back down after a moment of no motor activity. Does it?
It doesn't go back to 82.7v, it stays on 83.2v until riding it on road, I'll make another video next time and also measure the battery with a proper voltmeter instead of just the display
 
THe spike is probably electrical noise in the system, possibly (but not likely) a poor solder connection somewhere in the voltmeter circuit part of the system (usually inside the controller, but possibly within the display; usually a voltage divider and sometimes an op-amp for buffering before going into the MCU).

How the display metering system works will determine what readings it gives and stays at. If it is poorly designed it could keep increaseing the voltage reading after a spike, instead of properly averaging.



But you have another problem, if that final charge voltage of 82.7v is correct:

The voltage on your battery after charging before riding indicates it isn't balanced. At 4.2v per cell, for a 20s battery, it should read 84.0v. An 84.5v charger works for that; your BMS shuts off charging once any cell reaches it's HVC (which is probably 4.2v).

But if the cells are not well-matched and the pack is not well-built (both very common problems), some cells (or groups of them) will have less capacity and higher resistance, so they will reach HVC first, and shut off charging before the rest of the cells are full, so the total pack voltage is low.

With a final charge voltage of only 82.7v, that's 84v - 82.7v = 1.3v. If that is distributed among all the other groups, it's not such a big deal, as little as 0.07v difference per cell from full. But if it is on just one group, that's pretty seriously imbalanced, as it would mean that the rest of the groups are at 4.2v while one is at 2.9v, which is very very low (empty!). Could be on any number of groups.

I would recommend opening the pack up, and checking the voltage on each group at the BMS connector itself (preferably on the solder joints on the back of the BMS, as that also verifies the cell connections to the BMS so you will know it is sensing them all "correctly").

THen list each of those group voltages here in this thread, starting at the most negative, and working your way up to the most positive, for all 20 groups. This will help us help yo find whcih group(s) cause the problem, and see if it is a significant problem, or one you can fix easily by leaving the battery on the charger longer (usually at least several hours--if it's a severe imbalance, it can take days or even weeks depending on the cause of the problem).

If it's a single group or only a few that are really low, you may have a cell defect problem, or worse you could have a BMS with stuck-on balancers that are killing your cells continuously whether you use the pack or not.

Or you may have a BMS with no balancers at all, and poorly-matched cells that are not equally capable; in this case the problem will get worse and worse over time, and faster the further it is discharged each time, under higher loads.
 
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