Voltmeter test - help

JED1990

1 mW
Joined
Mar 13, 2021
Messages
13
Hi guys

Someone has asked me to find out why their eScooter isn't powering up

Opened up the base and tested the battery which is current only at about 1v (it's a 36v 10s3p battery) so something isn't quiet right. Apparently the scooter has been stored in a garage for a number of months over winter....

The charger powers up, but a steady green light at all times, even when plugged in (indicating - no charge / full)

When I go to test the charger with the voltmeter I get small spark and have to withdraw. I have red probe on pin and black on outside rim. Positive first, negative after.. doesn't seem to like being touched! Any ideas to why?

I'm assuming at this stage , the issue is likely the charger or BMS?

Any ideas about testing the charger without sparking ?

Screenshot_20210410-014353.png

Screenshot_20210410-014422.png
 
Show a photo of the charger connector and how you are probing it.
 
JED1990 said:
Opened up the base and tested the battery which is current only at about 1v (it's a 36v 10s3p battery) so something isn't quiet right. Apparently the scooter has been stored in a garage for a number of months over winter....
That means the BMS has shut off the output to protect the cells from being overdischarged, and probably the input is also off to prevent them from being recharged as one or more groups has likely dropped below the safe recharge limit.

If you can open up the pack and test each cell group's voltage, starting from the most negative and going up to the most positive, you should end up with 10 voltage readings. List them all here, in that order, and we can help you figure out which (if any) are salvageable, and which have to be replaced.


When I go to test the charger with the voltmeter I get small spark and have to withdraw. I have red probe on pin and black on outside rim. Positive first, negative after.. doesn't seem to like being touched! Any ideas to why?
THe voltmeter appears to be correctly set and leads in the right holes, so it will not be placing any load on the charger to cause such a spark.

That implies something is being shorted by the probe tips of the leads. Show the connector, and how you are doing the connection with the meter, and we may be able to help figure out a better way.

When you do get the spark, does the voltmeter read anything at that moment? I see a Hold button--is that a manual function only, or does it also do a Peak Hold? If it does the latter, then when it is on it should keep the highest reading on screen even after you disconnect the leads.
 
Hi AmberWolf

So it appears the Voltmeter I was using the first time round was a bit dodgy. I've used a new one which is okay.

The cells appear to be grouped in 3's? ... which I'm still getting my head around (I'm relatively new to battery building) The arrangement of a 36v battery I've made before I arranged the cells in groups of 10s and then I connected those groups in parallel)


Here's the battery I'm dealing with
ATTACH]


The charger works as measured it at 41.8

The cells measure
0.74. 0.49. 0.93. 0.85
0.74. 0.49. 0.93. 0.85
0.74. 0.49. 0.93. 0.85
1.05. 1.05. 0.83
1.05. 1.05. 0.83
1.05. 1.05. 0.83
1.00. 0.82. 0.90
1.00. 0.82. 0.90
1.00. 0.82. 0.90

Hope this provides a little more insight... Seems some are quite low (0.49) so perhaps BMS is blocking any charging ?
 
that pack is dead.

the bms is doing its job by protecting the house from burning down when are trying to recharge it.

without a lab power supplly you wont be able to recover it if you even can recover it as the cells will be seriously damaged by now. without a very slow controlled current (think 50mA) you will likely burn down the building if you try to hotwire the charger.
 
JED1990 said:
The cells measure
0.74. 0.49. 0.93. 0.85
0.74. 0.49. 0.93. 0.85
0.74. 0.49. 0.93. 0.85
1.05. 1.05. 0.83
1.05. 1.05. 0.83
1.05. 1.05. 0.83
1.00. 0.82. 0.90
1.00. 0.82. 0.90
1.00. 0.82. 0.90

Hope this provides a little more insight... Seems some are quite low (0.49) so perhaps BMS is blocking any charging ?
Yes, those cells are totally unrecoverably dead. The BMS is blocking charging to prevent a fire.

A new battery pack is needed to fix this problem. :(
 
JED1990 said:
The cells appear to be grouped in 3's? ... which I'm still getting my head around (I'm relatively new to battery building)
This is the normal common way of doing it.


The arrangement of a 36v battery I've made before I arranged the cells in groups of 10s and then I connected those groups in parallel)
That would be an uncommon way of doing it, because you need three BMS's to monitor and balance that style of pack.
 
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