Battery isolation fault help

[ManxViking]

Cheers Moz.
I will take out the pack tomorrow and check everything again. Are there any videos that you know of that show how to test the wiring from the pack to the motor etc.
I find it difficult to understand that one smashed up mg and one with a little bump have the same issue and the fact I can't find it is p**sing me off ? Got no transport which causes all sorts of problems. I have a friend with a Hyundai Kona with the same issue so it must be something generic across all EVs.
Cheers,

David

 

[MozFromOz]

Sorry David. I don't know of any videos illustrating the pack to motor wiring.

One thing more that I forgot to mention is borrowing a Megger (high voltage insulation tester) from someone and redoing your pack insulation tests with that. Dala's video here shows you how to use it. This is the best way to be absolutely certain you have sorted out leakage in the modules. If you find any leaking to the frame. Clean them up with lots of electrical contact cleaner spray.

Ray

 

[ManxViking]

Took the battery out again last night. No moisture this time as you can see in the photos.

 

[ManxViking]

Ok. Not sure what I've discovered however if you look at the attached photo I took a voltage reading from the positive to the frame of the battery pack and a reading from the negative to the pack frame also. There were a few batteries that showed zero which I can only surmise that those batteries are not leaking voltage to the pack frame .
The remainder of the batteries had various readings as seen in the picture. I don't know whether or not the BMS connection was causing an issue so I removed the BMS connections and redid readings from the last few batteries, those numbers are on the far right hand side.
If anyone can advise what I should try next, I have ordered an isolation tester which is coming tomorrow and once I am up as I am back to work tonight, I will go back up and test again the batteries using that tester and see if there is any difference.

Many thanks for all the advice so far.

David

 

[ManxViking]

As an update, I've decided to look at the highest reading pack and apparently you can remove the top plastic cover. I will do that tomorrow and see if the connections inside are either wet still or maybe have rusted on any of the points of connection.
Will update with photos.
David

 

[MozFromOz]

Hi David.

Are the battery modules still interconnected to each other? They each need to be fully disconnected for the leakage tests to be valid.

If the readings were taken as above, then eack pack with a non-zero reading needs cleaning up. Yes take all the covers off but be extremely careful with your tools as a dropped screwdriver or wrench will end very badly.

Anywhere you find corrosion or powdery residue, clean it up with a stiff paintbrush, contact cleaner and a rag. You need to get every module back to reading zero volts or preferably safe readings on all with the Megger as recommended before.


Good luck
Ray

 

[ManxViking]

Good morning Ray,
Yes, all battery modules were disconnected from each other.

I am a little twitchy about cleaning contacts on each module as you've mentioned but hopefully this will sort the pack well enough to see if the car will take a slow charge and then finally move....

Wondering if i will need to somehow get all the packs to the same voltage prior to rebuilding the pack? What do you think? Or will they balance themselves once connected to a home 13a charger?

Thanks for your advice, much appreciated.

David

 

[MozFromOz]

Hi David.
I understand it's all new to you but believe me when I say you have to be thorough.

I recall you saying that the pack is at a very low state already. Water ingress can cause some discharge all of its own. Any imbalance between cells, not just modules will reduce range so it's important they are within 20mV or better. if you have imbalance it will need to be addressed manually as the BMS has very little balancing capability. It expects the cells to be all of a similar state of health.

Ray

 

[Coulomb]

I'm late to this thread, but make sure that the auxiliary (12 V) battery is good, and fully charged. "Christmas tree" dash lights can result from a poor 12 V battery causing corruption of CAN bus packets, and/or upsetting some of the many computers.

Wondering if i will need to somehow get all the packs to the same voltage prior to rebuilding the pack?

It's probably worth checking them all by multimeter. If one or two are significantly (more than a few percent) different to the others, it might be worth opening the pack and balancing the cells inside. I use a current limited power supply; dual power supply (make sure that the outputs are isolated!) lets you charge two cells at once. If one is too high, I use a set of car headlamps with clip leads (you could get away with one) to discharge one cell at a time slowly. I put the headlamps into old ceramic cups. Even at around four volts on a 12 V bulb, they get significantly hot.

 

[ManxViking]

I am thorough, or think I am. I definitely don't take anything for granted.

To balance the battery modules to at least the same voltage that may take a while as I only have a lab power source but appreciate that's a necessity not a nice to have prior to putting the pack back in the car.

I had read somewhere that the MGs have a setting in the car ( once the packs back in ) that allows for a battery balancing to be run? Any idea?

Cheers,

David

 

[MozFromOz]

All EV's carry out "top balancing" at the end of a full charge but it can only cope with a very limited range of differential. The MG's are no different. @coulombs advice on how to do it is on target. Allow yourself a week.

Ray

 

[ManxViking]

Hi Coulomb,

Thank you for the info. I do have a small power draining unit that I used on my 48v packs, basically it heats an element and you can adjust the draw to suit. Maybe that will do it. All the cells are at different stages of charge it seems, so will have to bring them up to a set voltage. I guess this will then help going forwards, with fast charging problems etc.

The other point is I have a second zs EV, a 21 plate with 10,000 miles on it. Am wondering if its worth pulling that battery out and utilising modules, but that car's done a lot less mileage than this one ( 56k) I'm working on currently and thought mixing modules from different aged packs might not be the best.

David

 

[Coulomb]

I had read somewhere that the MGs have a setting in the car ( once the packs back in ) that allows for a battery balancing to be run?

Not a setting, at least that I'm aware of. Just charge the battery to 100% from AC and leave it there until the MG logo goes from on solid (balancing) to off. It's of course "breathing" while normal charging.

Might be worth monitoring the charge power during the first balance or two. After an extended period with no charging or driving, it may take a few long balances. I believe that balancing happens above 93% SoC (I don't know if that's indicated or real SoC), so to force another charge, drive it a bit till you get under 93%. For our model, you only see that when plugging in and charging, or via an OBD2 app. You could just drive it until you lose the first "brick" on the dash (the 8 LEDs that give a crude estimation of SoC). I believe that's 91% SoC (probably display SoC, again I'm not sure).

 

[Coulomb]

mixing modules from different aged packs might not be the best.

Definitely don't do that if you can possibly help it.

 

[ManxViking]

I guess there's no other way of doing it but I wonder what's going to be the best voltage to get them all to be the same? Do I just take the highest and charge all to that number?

 

[MozFromOz]

Yes, given the pack is already pretty low it's just a case of bringing all the cells to equal the best one.

In answer to your question about mixing modules, I agree with @Coulomb . Not something you'd do unless absolutely necessary for example one of the modules has cells below 2v. You wouldn't want to put such cells back into service.

Regards Ray

 

[ManxViking]

Got some photos for viewing

 

[ManxViking]

The concerning thing for me is that i cannot find any corrosion so far. The odd thing is that the batteries which had no visible water ingress on the pack floor, the 3rd row at the back of the pack, 16,15,10,9,4 and 3 are all the ones that are fine and showing zeros for voltage to the pack.
Even after making sure EVERYTHING has been disconnected and the battery is free standing, it still is showing voltage going to the pack? I thought if the bms cables were wet or corroded then i could work with that but there are no visible signs at all.

Any thoughts?

Thanks,
David

 

[MozFromOz]

Hi David. Yes looking at the photos I agree there's nothing obvious showing and the cells in the pack seem to be welded to the link straps so they cannot be disassembled further.

Are the cells in plastic or metal jackets? I can see aluminium under the plastic top frame.

 

[Coulomb]

Even after making sure EVERYTHING has been disconnected and the battery is free standing, it still is showing voltage going to the pack?

Are you saying that you can measure voltage at the main terminals of the pack, when the contacts should be off? If so, both contactors must be leaking. [ Edit: Assuming that the contactors are inside the main pack. ]

You keep talking about voltage, not leakage or conductivity. Many meggers can be used as a voltmeter as well as as a high voltage ohmmeter. Are you using the test button and the 500VDC setting? Testing at low voltage, as when using the megger as a voltmeter, can produce different results. Some leakage will only show up at high voltage.