Hot-rodding the Toyota MGR

[pearl62]

I am thinking I could use the voltage doubler in the Toyota inverter. I will just be providing a compatible battery voltage to the input. Toyota states 288V nominal for the Highlander, and I will be right there. The Soliton1 controller can accept up to 340V max.

I think the C rates you are quoting are for the Enerdel power cells. I will be using their energy cells, so the C rate drops to ~2C continuous, and 5C peak, though I have seen characterization which shows these rates to be somewhat conservative. At 6P I will already see a per 'cell' impedance drop from 0.7mOhm on the old Thunderskys to ~0.45mOhm.

Here's a basic floorplan showing old pack vs new pack, and a placeholder for the MGR. Mounting it in reverse would be the best way, as mounting it normally would require putting the batteries out beyond the rear axle line.

[e*clipse]

Yea, packaging is interesting. There are definitely big dynamic performance benefits by carefully working this part out.

On mine, I'm using the back seat area; trying to place the cells as low and centered as possible. So far it looks like I will be able to get a 55%rear-45%front weight distribution with a much lower moment than the original car.

I will be able to orient the motor facing forward in the rear by building a new suspension subframe. If I do it right, I might be able to get rid of some built-in understeer. In the front, it will have to be oriented forward to clear the steering rack.

The cell I was looking at was the Enerdel "moxie" cell:
http://www.enerdel.com/specsheets/en...ell__Final.pdf

What are your plans for linking the cells?

[pearl62]

That's the same cell then...

The cells are pretty easy to link up. You can see in the photo below a 4S 6P stack I created. I just need to get some bus bar material and create a drilling template to drill them at the sizes I want.

[e*clipse]

That looks very nice.

For my car my calcs show I could reduce the pack weight by about 1/2, compared to the Nissan Leaf modules I've got.
Nissan leaf based pack - 2p, 180S, 28.35kWh, 675V nominal, 754lbs
Enerdel pack 2p, 180s, 21.0kWh, 657V nominal, 356lbs

The tough things with the Leaf pack -
Each module contains 4 cells in a 2p 2s configuration. They are difficult to dissassemble, so you're stuck with the module configuration. In order to get the right voltage, I must make a pack with "too much" capacity. Although that's not a bad thing, it results in considerably more weight.

Making some bus plates would be very easy - there's a local shop with a laser cutter that could make them for very little. In fact, a "mirror image" design would only require 1 part (less set-up cost) for both jobs.

Is that Enerdel plastic cell clip?
If so, it's designed to hold 2 cells, right?

What's the weight of 1 cell pair and a clip?

And seriously - I'm very interested - it would drop the finished weight of my car by 300lbs!! - what's the price for a cell and clip?

Thanks a bunch,

E*clipse

[pearl62]

Wow, I didn't realize the Leaf pack was so heavy...

You can get some more details on the various assembly bits here: CustomProducts/EDI/EnerdelBattery - Elithion.

I just got the cells, compression bars, shims, nuts and bus bar covers only, so no end plates or bolts, which is fine as I am making my own module sizes to fit by battery boxes. I like that I can just assemble them any way I want, but the pieces common to any pack configuration are already provided.

[e*clipse]

Thanks for the info!

A major part of the Leaf weight is the module structure. Along with the plastic seperators, etc. (which are probably similar in weight) there is a copper bust bar setup and the "tuna can" protection. You can disassemble them; there's video about that, but it seems like a major PIA.

Also, the cell capacity is about 21Ah, 40% more than an Enerdel cell. Also, they are paired to provide 42Ah. That's fine if you want the capacity, however it does result in a heavier pack for a given voltage.

The Enerdel cell pair would hit a "sweet spot" for my voltage/capacity needs - IF a pair can supply about 350A to 400A.

Did you get the parts from Elithion?

- E*clipse

[pearl62]

I think 2p might be pushing it for that kind of current. I am going 6p mostly so that I can be confident about getting 500A. From the testing data I have seen they can deliver more without much temperature rise, but I also want these cells to last a while...

I will have a good BMS on them too, so they'll be well managed.

[pearl62]

Originally Posted by e*clipse

Is that Enerdel plastic cell clip?
If so, it's designed to hold 2 cells, right?

Each assembly of 2 cells in 2p comes with some surrounding plastic that clips together with a heatsink in between. There is also some special foam provided to provide even pressure on the adjacent cells. There are some good pictures here.

Originally Posted by e*clipse

What's the weight of 1 cell pair and a clip?

I weighed the 24 cells shown on a bathroom scale (not the most accurate I know) and it came to ~26.4lbs. That doesn't include the end plates, 4 bolts to hold the stack together or bus bars. I am using 1.2lbs/cell as a good estimate of per cell weight with all this extra stuff.

For bus bars I am going to use 1/8 x 4" 6061-T61 aluminum. From ampacity charts, it should be able to carry ~585A with 30C temp rise, and 780A with 50C temp rise. As I should be seeing no more than 600A peak for only short durations, I think I should be fine. I'm seeing much higher temp rise than that with my current copper bus bars from Thundersky (and 1000A peak).

[e*clipse]

Originally Posted by pearl62

I weighed the 24 cells shown on a bathroom scale (not the most accurate I know) and it came to ~26.4lbs. That doesn't include the end plates, 4 bolts to hold the stack together or bus bars. I am using 1.2lbs/cell as a good estimate of per cell weight with all this extra stuff.

For bus bars I am going to use 1/8 x 4" 6061-T61 aluminum. From ampacity charts, it should be able to carry ~585A with 30C temp rise, and 780A with 50C temp rise. As I should be seeing no more than 600A peak for only short durations, I think I should be fine. I'm seeing much higher temp rise than that with my current copper bus bars from Thundersky (and 1000A peak).

Ok, so a set of 4 cells 2s2p (equivalent to a Nissan Leaf module) would weigh about 4.8 lbs. However, to ensure the cells can handle the current, you're using 6p instead of 2p. The 500A is similar to the current I'll be using in my 4 motor system. If your #'s are correct, and you do need to limit the current to 5c or 6c, then I would also need a 6p Enerdel pack. The equivalent "module" would then be 2s6p and weigh 14.4lbs.

Hmmmm - that would actually weigh more. Of course this is all predicated on how hard one can push the cells. Maybe I'm planning to push the Leaf cells to hard.

Another question - do you plan to do any cooling for the cells? Are you concerned with the hotter bus bars actually causing heat to go into the cells, rather than being a cooling opportunity?

Thanks again for information and discussion. It's nice to be able to compare systems like this.

[pearl62]

For the Leaf cells I've always used 4c continuous and 9c peak, which is what Hybrid Auto Center states. That would allow 2p. Remember that Enerdel 2p would be 35Ah, while Leaf 2p would be 62Ah... not exactly apples to apples.

For the capacity I am after (~29kWh) I would need 6p Leaf cells anyway, for capacity not peak current.

Remember, the temp rise of the bus bars at peak current is probably much less than the temp rise of the cells! I just need to keep it mind. I am thinking of implementing cooling via these Wakefield-Vette cooling plates.