Aftermarket iMiEV battery upgrade project

[T1 Terry]

I'm not sure if these are the same cells, But Jan from the Adelaide branch of the AEVA had his Prius burn to the ground after a short between a cell case and the chassis. I think it was actually the aluminium box he made to hold the cells in the wheel well of the Prius, but that was attached to the body. It actually blew a hole through the aluminium box and the steel floor I believe, so not just a bit of a zap.
I've decided to avoid the aluminium cased cells completely unless I can build them into separate cell groups with full insulation around each. Much like the way the cylindrical cells for push bike batteries are built.
Maybe the LTO cells in their own poly boxes flooded with the Novec 7100 fluid to keep them cool.

T1 Terry

[jonescg]

Yeah I fully expect any metal cased battery to be live to the case now. Rather disturbing the spec sheets mention nothing about this.
I think the FR4 will work OK. Not ideal, but what can you do.

[is0lated]

I'm not sure if I've missed it but how are you planning on adding bus bars to the batteries?

I've replaced a couple of cells in my minicab with cells that look to be the same kind and had some trouble attaching to the terminals. I couldn't get solder to stick properly and tapping threads was a little too fiddly for my liking, I ended up leaving the nickle strips on and soldering to those but it seems like you're past that point. If you do end up drilling and tapping I seem to recall the negative terminal is 4mm thick (or possibly 3mm) followed by 1mm of plastic insulation then you hit the positive battery (ask me how I know ). You probably won't need to bother tapping either, I found that whatever the terminals are made out of is soft enough for screws to cut their own thread once you've got the right sized hole drilled.

Also, be careful with the CMU boards. I've found them to be surprisingly sensitive for single sided, conformally coated PCBs. Although that might have been the spray foam I used as spacer in the first cell swap

[jonescg]

Good question... I was planning on getting some 2 mm copper busbars made up with enough cross-section for about 40 mm2. Unfortunately, one crappy little M4 screw hole is pretty ordinary contact, so I plan on putting a kink in the buslink just to the side of the screw hole to ensure some decent surface mating pressure.

cell terminals.png (10.9 KiB) Viewed 2108 times

Still, it's far from ideal.

[T1 Terry]

Yeah I fully expect any metal cased battery to be live to the case now. Rather disturbing the spec sheets mention nothing about this.
I think the FR4 will work OK. Not ideal, but what can you do.

What thickness FR4 are you using? After a few email discussions with Weber he mentioned another drop in battery producer was using 12mm polyethylene sheets between the cells but he was using the plastic cutting mats from Woolies, Bunnings etc https://www.bunnings.com.au/avanti-flex ... t_p0155338. I had mentioned before about the BBQ plate mats but Weber mentioned they are very easily damaged.

T1 Terry

[T1 Terry]

Good question... I was planning on getting some 2 mm copper busbars made up with enough cross-section for about 40 mm2. Unfortunately, one crappy little M4 screw hole is pretty ordinary contact, so I plan on putting a kink in the buslink just to the side of the screw hole to ensure some decent surface mating pressure.
cell terminals.png

Still, it's far from ideal.

Maybe you could use the method GBS use with their cells, 4 screws to hold the tab onto the terminal .... although I'm not certain that isn't the path that the electrolyte uses to escape and stink the car out each time it's charged ... or even left sitting with the windows up actually ....

T1 Terry

[jonescg]

I was planning on using 0.8 mm thick FR4. I used to buy big sheets of it from Regal-Beloit in Welshpool, but I think they stopped selling it. Now you have to go through a wholesaler to buy it. I like FR4 because it's tough, strong and is like kryptonite to electricity.

As for the buslinks, I don't want to go near drilling another hole. Gives me the heeby-jeebies already.

[T1 Terry]

I was planning on using 0.8 mm thick FR4. I used to buy big sheets of it from Regal-Beloit in Welshpool, but I think they stopped selling it. Now you have to go through a wholesaler to buy it. I like FR4 because it's tough, strong and is like kryptonite to electricity.

As for the buslinks, I don't want to go near drilling another hole. Gives me the heeby-jeebies already.

https://www.kdfasteners.com/thread-cutting-screws.html Just make sure the screws are short enough not to go right through the terminal boss. Pre drill the busbars so the hole location is easier than trying to match up the terminal holes to busbar holes. If you use a slightly smaller drill and add a depth gauge by using a terminal out of a BP connector screwed to the drill bit .... more reliable than tape or a chalk mark

T1 Terry

[wovenrovings]

Geez, no pressure. Only 100 iMiEV owners hanging on this thread right now!

Make that 101. My newly purchased iMiev is on its way.

[jonescg]

I've decided to go with polycarbonate and screws, but with a new PCB which acts as a blanking plate for the original BMS.

This gives an indication of size:

Basic layout.jpg (193.76 KiB) Viewed 1869 times

I've decided to pack the cells close together to minimise the amount of work needed, as well as making the copper buslinks a bit more manageable. It means there will be some overhang at the other end of the BMS board. Fixing the cell modules into position within the floor will take a bit more thought.

I will use the M3 nuts I usually use for my termination kits as spacers to which the original BMS will screw to. Something a bit like this?

Cell top PCB.JPG (70.08 KiB) Viewed 1869 times

[jonescg]

I've made some more changes to the board, including screw holes where this sits atop the module. Also drawn a bit of a plan together for the two 4-cell modules in the centre of the battery. These will be a bit trickier as space is very tight, and it will call for an extension of the BMS wiring. Once I order all the parts it should all come together pretty quickly.

[jonescg]

Also just realised I'll need to build a second board for the two 4-cell modules. Unfortunately I can't use the same PCB for both.

[jonescg]

And finally, I just realised that the BMS mounting boards might be a while... Coronavirus appears to have held them up a week or three. As it turns out the epicentre of South Korea's epidemic was a Hyundai factory. So my Ioniq might be a while yet.

[jonescg]

OK so an interesting development (which is of limited value to this current project) but a 93 Ah cell with very similar dimensions to the LEV50N cell has come up.
I'm going to see if it's possible to re-build all modules with the bigger cell. Basically a $11,000 battery plus a couple of day's work to repack it all.
Only issue will be making sure the BMS plays nice.

[richi]

Ohhh, so not the SDI 94 Ah cell? I'm going to hazard a guess that the BMS will track down to zero blobs for the top 50 or 60 Ah, but the car will continue to drive until the worst cell reaches a critical Voltage, lighting Mister Turtle. GOM might be similarly weird.

[brendon_m]

That's would certainly improve range

[jonescg]

Yes they appear to be a near rip-off of the SDI cell, but the dimensions are awfully close to that of an LEV50. Slightly shorter. It would make for a far more elegant swap, that's for sure.
No idea how it will impact the BMS; all I can think is that it's capacity to self-learn will be overwhelmed.

[jonescg]

Basic details:

[richi]

Nice. Same terminal style as the LEV series, or is it solder as with the cells you were looking at before?

[jonescg]

No they come with M6 threaded holes. Not ideal, but workable.
Cost is about AUD$11,600 including GST to replace an iMiEV worth of cells, and maybe a couple of days work while you fumble your way through it.

[jamie85063]

I am liking the sound of these 93Ah cells so you would get almost double the original range for similar cost to a standard replacement pack? And these should work in a Minicab as well I would assume? As I would like a Minicab only thing is I need it do be able to do a minimum 200klm on a charge.

[jonescg]

Sounds like a good choice for the minicab. I'm happy to look after WA/SA enquiries but I think Oz DIY in Brisbane is onto these on the east coast.

[jamie85063]

Cheers thanks for that.

[mark_hetho]

If I'm not mistaken these are much shorter (115->85), about the same width (44->43), but slightly longer (171->173)?
I supposed if there are 2mm leeway on the width, it should be possible to pack the rest of the space out. Presumably there is a weight saving along with a capacity gain!

[jonescg]

The height difference is consistent with the LEV50 pack having terminal studs, versus terminal pads. It checks out.
They are heavier than the LEV50 cells, but not mya great deal.