i-Miev Battery Cell Testing

[Gary12345]

Hi all,

I am the owner of an i-miev from the UK - it is a 2011 with 11k miles, and has been sat for a few years unused, ever since one cell went low and the BMS refused to charge (I have never driven it, I bought it in this state to try and save it from the scrap yard !).

I am going to take out the battery pack and test each cell, so that I know whether the pack is any good (i.e. how many cells need replacing). I am trying to work out what I can use to test the cells, that doesnt take forever ! I've searched online and on forums and can't see anyone testing these cells and how they did it.

So far I am thinking of using a powerful RC charger, one that does 10A+, either a dual or quad charger so I can charge 2 or 4 batteries at once. Then get 2 or 4 battery capacity testers, i've seen some on ebay (and used similar things in the past), something like ebay item 183506412814. It doesnt mattery if it is not 100% accurate, I just need to identify bad cells.

Depending on the number of bad cells will determine the next steps for this car ! I'm excited to work on this vehicle as i've always been interested in batteries and charging technology and have built my own hobby battery packs in the past, so have experience with charging/testing/building multi-cell packs.

I have a copy of the Mitsubishi removal procedure for the battery so should be OK there - it might take me a while tho !

Any thoughts you guys have on better ways to test these big cells is useful - from the specs of this car these cells have to take up to 150Amps charge and discharge which is pretty impressive, but I can't replicate anything like that without very expensive kit, so it will be a lot slower my way !

Thanks,

Gary.

 

[kiev]

Howdy Gary, welcome to the club.

If the BMS wouldn't allow charging due to a low cell, then the rest of the cells could actually be full.

i would recommend that you get an OBDLink LX dongle from Scantool.net and the Android App, "Canion" from emobility on google. Then you will be able to see all the cell's voltages at the same time on a graph to identify which one is the bad cell and the state of all the rest.

Even if there is more than one worn out or weak cell, it will be quicker to use the car charger and canion to get the car running and charging and determine the pack condition, than you could ever do with your approach. It's just a matter of whether you want to get the car on the road or play with batteries.

There is another consideration, that in your 2011 car, chances are high that the cells were made in 2010, and they are now in the 9th year of their likely 10 year lifetime. So not much future in trying to restore an old pack if you are wanting to drive the car. In that case find a younger-aged pack from a salvage yard (if possible) and keep on driving...

 

[Gary12345]

Hi there, thanks for your input.

I do like playing with batteries but would like to get it working fairly quickly if possible so appreciate your input. You are right that with the battery pack in the car is the fastest way to find bad cells.

I'll order the ODBC adapter and I have an 8 block of the cells from another vehicle - i'll test each of these to find out how good they are, and use Canion to determine what cells are low, swap those out and see how it performs.

Maybe lots of cells in the pack are bad, who knows but the car was cheap and will be fun to find out what state it is in. If the pack has lots of bad cells i'll strip all the electrics out and offer them for sale to other owners to fix theirs.

Thanks.

 

[Don]

I think in most cases, a 'bad' pack stops functioning because of just 1 or 2 cells, so your 8 pack of replacements may be all you'll need to get the car back on the road

Don

 

[pbui19]

The challenge is how to balance the cells with respect to each other, since they are all in series ? When I rebuilt the Prius' pack, I had to connect all the modules in parallel for a couple of days while exercising slow up/down charging. At least with the Prius pack being NiMh, one can top balance each cell with a slow charge rate as a full NiMh cell simply dissipates heat. LiOn doesn't do that.

 

[Gary12345]

Hi all,

pbui19 - Cell balancing is not a problem, since lithium batteries do not like overcharge, they are installed with a BMS which will balance charge all cells to the correct voltage, as happens in the i-miev. So as long as I have decent cells and get them within the 3-4.1v range it should charge them all up to 4.1v.

Don - I very much hope so !

Thanks all !

 

[pbui19]

I think you are referring to charge shuffling. I am not sure if it's possible for deeply out of balanced cell, and if it does, it may take a really long time. Imagine a worse case scenario where all cells are around 80% SOC, and the one newly swapped cell is at 10%. The available range would also significantly diminished until that one cell comes up in SOC.

 

[Gary12345]

Hi, any new cells I put in will be somewhere around 50% charge, then hopefully the BMS will be happy to charge them all up to full. I'll get the Canion information out also before dismantling so I know what voltage all cells are at.

Thanks.

 

[JoeS]

Gary 12345, unlike LiFePO4, our cell chemistry is such that voltage fairly well reflects State of Charge and doesn't sag, I think you'd simply measure one of the other cell's voltage and simply charge the replacement to match.

 

[1kaspars]

what about warranty? Isn't it 10 years / 100'000km ?

 

[Gary12345]

The 10 year / 100k warranty only applied to the first owner, subsequent owners I believe it is 5 years, either way i'm 100% sure its out of warranty !