Battery isolation fault help

[ManxViking]

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.

Good morning Ray.
They are in metal jackets.

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.

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.

Hi Coulomb.
Yes, the tester was on 500v. Since 2/3rds of the pack has faults it is definitely something to do with the water ingress i found. I ordered an isolation tester which arrived last night but as i work nights i wont be able to use it till i'm up later this afternoon.
I guess that as it was 12 of the 18 cells which showed this issue maybe theres something inside the pack which i cannot see which has been damaged further. I'm considering removing one of the two modules, or both, from the pack and look at how to take it apart? I can see that all connections are laser welded so not sure what i can do except take all the bad packs home and stick them in my small box room with the dehumidifier on full blast for 2 days?

 

[Coulomb]

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.

If you mean that you measure zero volts from one terminal of a 6-cell module to the metal case of the battery (is there a metal case? Else use the jacket) then this is what you expect for a good module. You might even measure a small voltage that "waves in the breeze", just like when you wave the multimeter leads in the air, not connected to anything. That's just picking up stray electric fields and rectifying hum from 50Hz mains wiring inducting into the leads.

It's when you measure a solid voltage from terminal to case that you know that there is a leakage. You should check both terminals in case the leakage is at the first terminal. From the measured voltage, ~3.5V from one end indicates that the leakage is between the first and second cells, sevenish indicates the next connection, and so on.

 

[MozFromOz]

Hi David.

Here's what I'd do next. Take one of the modules, say the worst one out of the pack. Take another reading from the shells/frame to the module terminals again just to confirm the reading. Then soak the top of the module in contact cleaner spray. Contact cleaner is a dielectric fluid and should dissolve any salts hiding around the place.Try aiming it under the link straps between the cells. Let it soak in for a couple of hours and check for leakage again. If it starts to improve then you are on your way. If you have compressed air you can blow it out and repeat the process. The contact cleaner won't hurt the cells at all.

Ray

 

[Coulomb]

2/3rds of the pack has faults

I guess that as it was 12 of the 18 cells which showed this issue

I'm used to "pack" meaning the whole battery, i.e. all 108 cells. I would call the set of 6 cells a module. The cell of course is one individual lithium ion cell, 3.5-4.2 V.

I'm considering removing one of the two modules, or both, from the pack and look at how to take it apart?

Oh, so the pack is split into two distinct halves? I've not had a chance to digest the photos fully as yet. If you call these halves a module, then perhaps 6 cells a block? Just so we can understand each other.

I can see that all connections are laser welded

Ah. I initially thought you meant the cell to cell connections were laser welded, but I think you haven't gotten inside those 6-cell modules yet.

so not sure what i can do except take all the bad packs home and stick them in my small box room with the dehumidifier on full blast for 2 days?

I suspect that you're going to have to get inside the 6-cell modules somehow. Are you totally sure about this laser welding? It looks to me that the interconnects should be removable, probably by pushing some orange tab and pulling up. The orange plastic seems to be two distinct parts. But perhaps that's just to allow for slight movement without straining the cells and/or connections.

Dehumidifying might help, but I suspect that there will be some residue that needs cleaning off with alcohol or similar. It won't have been demineralised, perfectly clean water that ingressed.

 

[ManxViking]

Thank you both.

I tried the manual as the link was posted by #Fred12345 on the 1st page. I couldn't get set up as it wanted my business details, which i don't have as I'm not a garage however he managed so i need to try again.
I can confirm that the readings have remained the same on those 2 modules, I will do as suggested and take the tops off the 2 worst offenders, as seen as open in the pics, and soak / clean them using the electrical contact cleaner and a toothbrush and see how it goes.
I've already had the 1st 2 rows of cells out before when i was removing the water from the packs shell. The orange tab is just a cover to the connectors for the busbars.
The fluid inside was milky and was absolutely stinking and was on all the connections and bms cable connections as well so i will try to soak and clean everything from these 2 modules.

Sorry for the incorrect use of the correct terminology. I'm getting there.....slowly

 

[Coulomb]

The fluid inside was milky and was absolutely stinking and was on all the connections and bms cable connections as well

Wow. You have your work cut out for you then.

 

[MozFromOz]

Given how otherwise clean the top of the modules look in the photos I guess the worst of the conductive salts are going to be under the welded on cell link straps. Hopefully you can find something that you can push in under there to help clean it out with the contact cleaner fluid. Might not be much there but it doesn't need much to cause leakage. Good luck.

 

[ManxViking]

#Fred12345 please see what i get when i try to join the R&M MG website

#Fred12345 please see what i get when i try to join the R&M MG website

Update,
Me being dumb again.... Managed to navigate to the correct section....

Update,
Me being dumb again.... Managed to navigate to the correct section....

I think 21 euros for a day with printing rights is ok. Will have to do it from work but would have been happier as a download as i could put it on the laptop. Never mind, the car saves trees, and the diagnostics printing will use several up.....

 

[fred12345]

I tried the manual as the link was posted by #Fred12345 on the 1st page. I couldn't get set up as it wanted my business details, which i don't have as I'm not a garage however he managed so i need to try again.

In the field "type of customer" leave "person" and just move on, leave company data section blank

 

[shpub]

I think 21 euros for a day with printing rights is ok. Will have to do it from work but would have been happier as a download as i could put it on the laptop. Never mind, the car saves trees, and the diagnostics printing will use several up.....

Print it directly to a PDF. When I got the data, it was shown as a pdf on the screen so I simply downloaded it. The really interesting stuff is not available unless approved by MG unfortunately.

Line insulation faults do not have to be a single fault. It is measuring the total resistance between the HV lines and earth i.e. the car chassis/body. Just like resistors if you have poor insulation in several locations that may trigger the monitor where that insulation level at one point won't.

Measuring voltage between the frame earth and HV leads, battery cells etc may or may not tell you anything especially if the batteries are all disconnected.

The monitor is usually wired into the HVIL system which when broken(O/C) disconnects everything. It is built into every HV plug and socket. Typically there are at least ten locations in the chain, anyone of them can disconnect the HV everywhere.

There are also pre-charge resistors which "leak" across contactors to prevent sudden current inrush when powered on. Depending on where the measurement is taken, not uncommon to see some leakage and assume the contactor is duff.

I would clean the contacts, measure the cell voltages and see if any are bad. Try charging that cell slowly - over a week or ten days at around 0.5A and it might recover. While they may recover, they will be a weakness so further testing may be needed. Yes it is a long slow business.

Be careful when removing stuff under the module cover - the connections can be very fragile and break.

 

[fred12345]

Print it directly to a PDF.

?

 

[ManxViking]

That's a good idea #shpub. I'll logon this evening and do that and download it to my laptop. Perfect ? ?

I'm going to remove the 4 worst modules, bring them back to my house to clean and test and charge to a set voltage. I will use the isolation tester to check before removing and confirm all voltages are the same as before when I wrote them on the cardboard. I'll note what the tester shows as a reading and compare to the modules I know are fine and post the results later on here.
David

 

[fred12345]

I'm going to remove the 4 worst modules, bring them back to my house to clean and test and charge to a set voltage.

as long as we don't read about it in the papers ... don't leave them charging indoors unattended, you never know ...?

 

[ManxViking]

As you can see, module one has a 500 volt resistance of 0.42 to 0.52 MΩ. module 2 has a resistance of 16+, I've done a video and will add to the next message if it's not too big to add. Module 5 was 0.45, module 6 was 16+, module 7 was 0.01. module 8 was 0.005, module 11 was 0.16, module 12 was 0.39, module 13 was 0.21, module 14 is 0.122, module 17 was 0.07 and finally number 18 module was 0.001.
Please see the photos as I hope I have set it up correctly in order to test the resistance but I have no idea what this information means yet, I need to research that later at work.
If anyone has any ideas on this? And if I have done it correctly or not?
Thanks,
David

Unfortunately I've been unable to add the video as the file is too large but basically when I had it set on the number two module or number six module the number started off low at 4, but went up and up and up and I stopped videoing after it got to 16. I can only assume that the two modules with the 16+ readings have a very big problem although the voltage across the module to the battery pack frame is not the highest out of all .
The modules which have the highest voltage loss against the frame of the battery pack actually have the lowest resistance. The modules two and six both had 16 plus readings but their voltage from the positive to the frame of the battery pack was 3.1 volts for number two and 12.6 volts for module number six.
If anybody can advise what these readings mean and what they think?
I have not got the electrical contact cleaner yet, it is due to arrive tomorrow therefore I will remove the two modules which have the 16 plus reading, the tester was set to 500 volts, and I will clean those as best as possible first.
Regards
David

The first two pictures are module six and the second two pictures are module two.

[ Edit Coulomb: Added that the measurements are in MΩ. ]

 

[fred12345]

Unfortunately I've been unable to add the video as the file is too large

upload it to YouTube and then post the link here

 

[ManxViking]

Thanks Fred12345 but I don't know how to do that....
David

Thank goodness for my 16-year-old son.....

 

[Coulomb]

If anyone has any ideas on this? And if I have done it correctly or not?

I think you're measuring just fine, but interpreting backwards. Measuring from the cell terminals to any metal case, we want ideally no leakage, i.e. no current flowing. Any current here is going to discharge the cells, and could potentially lead to electric shock, heating, and other bad things. So we want the resistance to this leakage current to be high, not low. That isolation meter is presumably reporting in megohms. So a reading of 0.001 means roughly one kilo-ohm. At 400V, that could lead to 400mA of current, or 0.4A, and 160W of heating. If there is leakage that bad from more than one point in the module, then some cells could be discharged and ruined. But fortunately none of your modules reads less than 21V (3.5V x 6 cells/module), so it doesn't look like you have lost any cells as yet.

Seeing the resistance go from 4 to 16 megohms is not unexpected where moisture is involved. I think it means that even those good modules (with the high isolation resistance) could well do with some cleaning and drying.

So when you take home the 4 worst modules, make sure these are the ones with the lowest isolation resistance readings.

 

[ManxViking]

Thank you so much #Coulomb.
It makes no sense to me as i'm not an electrician but once I have information I can be safe and ok for certain.
What confuses me is the different readings as there is no correlation to the voltage numbers i showed on the cardboard in an earlier post.

I'm thinking the best option is to take all 12 modules from the 1st 2 sections that showed moisture ingress?

From the numbers i don't really understand why the ones with the largest resistance are actually ok when there's a voltage showing from the module + to the main pack case?

Defo confused.com time for some YouTube learning i guess

David

 

[Coulomb]

Defo confused

It's tricky, to be sure.

Were all these readings with the modules still connected to each other? But by the looks, they're disconnected from each other.

The voltage measurement technique might not be as suitable for the case where you have multiple leakages. The megger measurements are definitely the ones to concentrate on now. Though you could use an ordinary multimeter on ohms range for quick tests without the hazard of 500 VDC. But of course once you think a module is fixed, the final test has to be on the megger.

 

[ManxViking]

It's tricky, to be sure.

Were all these readings with the modules still connected to each other? But by the looks, they're disconnected from each other.

The voltage measurement technique might not be as suitable for the case where you have multiple leakages. The megger measurements are definitely the ones to concentrate on now. Though you could use an ordinary multimeter on ohms range for quick tests without the hazard of 500 VDC. But of course once you think a module is fixed, the final test has to be on the megger.

All are disconnected entirely from each other.

If I get good readings after dried and cleaned I will just rebuild the pack and try it in the car. Got the car booked in for the paint shop so not a lot of time left to get it going otherwise will have to move the paint dates and lose the slot.

I have had another friend reach out to me as he's working on a Hyundai Kona that is saying isolation problem like my MG. Odd that it seems this fault, although common affects some cars that have been in accidents but not others. Anyway, will spend the next few days getting everything cleaned and dried as much as I can. I will video the cleaning and post on YouTube as well as at various stages of the battery pack rebuild and 1st turn on etc.

Thanks very much.

David