Grid Charging HV Battery, voltage too high?

Hey everyone,

I just finished replacing some dead/weak modules in my traction battery pack. I tested all the modules with a H4 headlight bulb, and measured starting and ending voltage. I reassembled the car with used modules, and performed the battery reconditioning process with a Prolong grid charger and light bulb discharger. However, when the battery was supposedly in the “balance phase” it charged up to 249 volts, which is a decent bit higher than the 235-240 volts the website says the battery would have settled at. Any idea what would cause this? Is it a sign of other bad modules?

Thanks

 

195,000 miles. I let it charge/balance for about 30 hours. After letting it rest for an hour, and trying to drive it, it’s pretty clear that there’s a failed module that I must have missed somehow. I guess it’s coming apart again tomorrow...

 

After resting for an hour the pack was at 233.5V. However the voltage of block 13 was a lot lower than the rest of them. I pulled the battery back out of the car, and it one of the modules (25 as I have it numbered, starting furthest from the computers) was at 7.3v, while the rest were all around 8.4. I pulled the battery from the car, and I’m going to re-load test all the modules. My guess is that one was weak, and the reconditioning process caused it to fail completely.

 

I ended up replacing module 25 today and reinstalling the pack in the car. I have it on the prolong charger now, and I’m going to let it charge/balance overnight. I load tested all the modules, and module 25, while it had a resting voltage of around 7.3V immediately dropped to less than 1V when a load was applied (could not even light the H4 headlight bulb) so it definitely needed replaced. I’m assuming that module had high impedance or something that raised the voltage of the entire pack (although I don’t really understand all the failure modes of NIMH cells). I found some mention on other threads in this forum about the voltage being high when a bad cell/module was installed in the pack. I’m hoping the new module solves the issue. I’m gonna keep an eye on the charger over the next few hours to see what voltage it stabilizes at. It’s currently at 233V. I plan to let it run overnight to balance the pack.

 

So that apparently was not the case. The prolong charger reached 245 volts, and I shut it off, not wanting to potentially cause damage by charging the pack at too high a voltage. I charged the replacement module to a similar-ish level to the others with an RC car charger, and I’m going to let the car sit overnight and bleed off any heat that may have been generated. I’ll try driving it in the morning and monitor the voltage of the blocks using a scan tool.

 

vvillovv, I think I'm going to take your suggestion and reach out to prolong tomorrow. I don't understand enough about the way the charger works to narrow it down to an issue with my battery pack, or a potential issue with the charger.

Just in case anyone is curious, here are the results of my load testing. I connected an H4 headlight bulb to each module for 120 seconds. The second reading was taken before switching off the load. There are some modules that are weaker than others, but nothing that stood out as needing immediate replacement. Module 1 is the module furthest from the ECUs. I did not try to rearrange the cells to match internal resistance. The one labeled "replace" is the used module that I replaced module 25 with. The lower starting voltage is due to a lower charge level than the rest of the cells already in the pack. I was a little hesitant to charge it not installed, since I had read about the modules swelling when charged outside the clamping force of the chassis.

Module, Starting Voltage, Ending Voltage
1 8.47 7.87
2 8.46 7.92
3 8.47 7.99
4 8.39 7.96
5 8.47 7.97
6 8.45 7.96
7 8.47 7.98
8 8.45 7.96
9 8.47 7.98
10 8.38 7.95
11 8.45 7.98
12 8.48 7.92
13 8.45 7.95
14 8.41 7.88
15 8.46 7.98
16 8.45 7.93
17 8.43 7.89
18 8.45 7.91
19 8.41 7.93
20 8.45 7.96
21 8.46 7.98
22 8.47 7.9
23 8.46 7.97
24 8.46 7.96
25 7.08
26 8.39 7.79
27 8.44 7.96
28 8.44 7.97
Replace 8.18 7.75

 

I believe that one of the replacement modules was bad, and I must have missed it with my load test. Monitoring the block voltages showed that it was still block 18 that was fluctuating. Since I need the car to be reliable, I decided to just replace the entire pack with the 2k1toasterpack. Hopefully should have that installed by tomorrow.