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Hi, Im looking into purchasing a first gen Miata to convert. I have some experience when it comes to working on cars (able to change oil, tires, radiator flush, remove both front and rear seats, change timing belts, change accessory belts, changing door panels, etc.)

I want to at least have a 100 miles per charge, and at least 300 HP. I also want to keep the cells as low as possible in the Miata. I plan on using a Nissan Leaf motor, coupled with a custom inverter (I have some options of what to use but open to opinions), Leaf DCDC Converter, CCS plug, and the use of either 18650 cells or SPIM08HP pouch cells. I have around 200 18650's that I'm currently testing, and about 32 SPIM08HP cells. I leaning more towards the use of the pouch cells however, due to their much higher MCD rate, and form factor.

Money is not an issue, and while Im not rich, I am more than content with saving cash up over long periods of time.
 

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How are you using the Leaf DC-DC?

Paul Holmes (P&S Power Electronics) sold me a control board to use with the Nissan Leaf inverter for $300. I just got it running Thursday, and it seems very good so far. I think that's the easiest option. You dont have to pay for/build the power stage as the inverter is bundled with the 2013 Leaf motor, and it's as close to plug and play as you can get. The price is right, too.

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I want to at least have a 100 miles per charge, and at least 300 HP.
...
I plan on using a Nissan Leaf motor, coupled with a custom inverter...
Hopefully you will only try to get this level of power very briefly, both because the motor would have cooling problems with any extended use, and because the battery won't handle it. You can only use 300 horsepower for a few seconds at a time in a Miata on the street anyway.

I also want to keep the cells as low as possible in the Miata.
It's going to be difficult to do that. With the transmission still in place (presumably), and the Leaf motor taking most of the engine space, the only space for battery which is really low is the bottom of the trunk.
 

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Hopefully you will only try to get this level of power very briefly, both because the motor would have cooling problems with any extended use, and because the battery won't handle it. You can only use 300 horsepower for a few seconds at a time in a Miata on the street anyway.


It's going to be difficult to do that. With the transmission still in place (presumably), and the Leaf motor taking most of the engine space, the only space for battery which is really low is the bottom of the trunk.
I gather that the Leaf motor is rated for 80kw continuous. Briefly jumping up to 300hp shouldn't be an issue, with appropriate cooling. I'd be more concerned for the light unibody, transmission, and rear end... That is far, far more power than that body was made to handle. Just something to check.

The Leaf motor is pretty small, honestly, and there's no accessory drive on the front of it, nor the need for a bunch of ducting. Creative mounting of the heat exchanger for the motor and inverter could help, too. I don't see why you couldn't fit a chunk of batteries up front, and some in the original gas tank location to stay near the car's original balance.
 

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I gather that the Leaf motor is rated for 80kw continuous. Briefly jumping up to 300hp shouldn't be an issue, with appropriate cooling. I'd be more concerned for the light unibody, transmission, and rear end... That is far, far more power than that body was made to handle. Just something to check.
It's an old car, and it's true that it wasn't designed for a lot of power, so repairing any structural rust or damage and adding some of the available structural braces would be wise. On the other hand, people have been swapping GM V8 engines into these cars for years, and no one bothers doing that with as little as 300 horsepower.

The Mazda transmission might be more of an issue if pushing the power that high; the V8 swaps change the transmission (and usually the final drive / differential as well).

The Leaf motor is pretty small, honestly, and there's no accessory drive on the front of it, nor the need for a bunch of ducting. Creative mounting of the heat exchanger for the motor and inverter could help, too. I don't see why you couldn't fit a chunk of batteries up front, and some in the original gas tank location to stay near the car's original balance.
Yes, in front of the motor is a prime location. Unfortunately that plus the fuel tank space won't be enough battery space.
 

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Haha, it depends on the GM v8. There are plenty that don't hit 300 hp XD

Even if they dont beef up the body, they should. You dont have to, but you will run into weird flex and cracking at weak points. It's cheap and the car will drive better. There's no reason not to, especially at those power levels.

I wouldn't be so quick to say things wont fit until he has some measurements. There may be space above the motor, as well, especially if he uses an early leaf motor and shifts the inverter.

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Haha, it depends on the GM v8. There are plenty that don't hit 300 hp XD

Even if they dont beef up the body, they should. You dont have to, but you will run into weird flex and cracking at weak points. It's cheap and the car will drive better. There's no reason not to, especially at those power levels.
There's no point in swapping in a low-power big V8 engine. You could, but that's not what sane people do.

But we agree that it would be prudent to strengthen the body structure.

I wouldn't be so quick to say things wont fit until he has some measurements. There may be space above the motor, as well, especially if he uses an early leaf motor and shifts the inverter.
Yes, but I was responding to the intention to keep the battery cells low. Most production EVs put the battery under the floor and seats, and that's just not happening in a Miata (or any car this small with seats and floor this low)... much of a sufficiently large battery is going to be relatively high.
 

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I want to at least have a 100 miles per charge, and at least 300 HP.
...
I plan on using a Nissan Leaf motor, coupled with a custom inverter (I have some options of what to use but open to opinions), Leaf DCDC Converter, CCS plug, and the use of either 18650 cells or SPIM08HP pouch cells. I have around 200 18650's that I'm currently testing, and about 32 SPIM08HP cells. I leaning more towards the use of the pouch cells however, due to their much higher MCD rate, and form factor.
If I found the right specs, those are 8 Ah capacity cells rated at an unlikely 200 amps maximum discharge rate. 32 of them in series would provide about one-third of the voltage for which a Leaf motor is designed, together at 200 amps they could deliver about 24 kW, and in total (regardless of series or parallel configuration) 32 would provide less than one kilowatt-hour (so enough for about 3 miles of range). So you would need hundreds more of these cells.... maybe a thousand in total. The 32 are just a start, right?

Similarly, 18650's are used in quantities of thousands.
 

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and the use of either 18650 cells or SPIM08HP pouch cells
That is the worst idea ever.

That's what I am doing. I am happy with my results. I have (had anyway) a bottomless source of free 18650s, enough spare time to test them, and I'm cheap enough to pinch every penny. And it's still a terrible idea.

I think it was Duncan who mentioned that, though it was talked about a lot, I don't think anyone has ever actually built an EV battery pack from 18650s.

Jehu built 1 cell big parallel cell for a vehicle just to show it was possible. A guy who has a ten million dollar battery recycling facility threw a bunch of old phone LiPos in a car and drove 1000 miles at highway speeds, but, beyond that, I don't think anyone's done it on a vehicle they'll actually use.

Buy used OEM packs. Get a part time job at MacDonalds in the evenings and buy used OEM packs.
 

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Discussion Starter #10
How are you using the Leaf DC-DC?

Paul Holmes (P&S Power Electronics) sold me a control board to use with the Nissan Leaf inverter for $300. I just got it running Thursday, and it seems very good so far. I think that's the easiest option. You dont have to pay for/build the power stage as the inverter is bundled with the 2013 Leaf motor, and it's as close to plug and play as you can get. The price is right, too.

Sent from my SM-N960U using Tapatalk
I've seen some videos of a homemade go cart that he made. Will definitely look into this option. Don't I need a Dcdc converter for 12V accessories like lights, switches, and AC?
 

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Discussion Starter #11
If I found the right specs, those are 8 Ah capacity cells rated at an unlikely 200 amps maximum discharge rate. 32 of them in series would provide about one-third of the voltage for which a Leaf motor is designed, together at 200 amps they could deliver about 24 kW, and in total (regardless of series or parallel configuration) 32 would provide less than one kilowatt-hour (so enough for about 3 miles of range). So you would need hundreds more of these cells.... maybe a thousand in total. The 32 are just a start, right?

Similarly, 18650's are used in quantities of thousands.
Yes 32 cells is what I have currently. I am collecting more each week (between 4-20 cells per week, depending on how much money I make).
 

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I don't think anyone has ever actually built an EV battery pack from 18650s.

Yes, i did a few years ago. Build 48 modules in 30P configuration made of Samsung 29E 18650 cells.

This all was for a Peugeot 106 Electrique that was originally running on Saft 20 Nicad 6V cells.


Was it succesfull: yes partially. :)
During the test drives after about 100km I decided to take the pack to the limit and wasnt carefull enough to monitor the lower voltage. It ended with burning up half of my pack because of the lower voltage. Luckily the car itself got saved. After diagnosing the cells and how they where constructed I decided to put that specfic project on hold (but recently picked up thinking about redoing it again).


So yes it can certainly be done, building EV batteries from 18650 cells as per DIY.
But one need to think about proper busbar sizing, protecting module covers/casings, module interconnections etc.
 

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Yes, i did a few years ago. Build 48 modules in 30P configuration made of Samsung 29E 18650 cells.

This all was for a Peugeot 106 Electrique that was originally running on Saft 20 Nicad 6V cells.


Was it succesfull: yes partially. :)
During the test drives after about 100km I decided to take the pack to the limit and wasnt carefull enough to monitor the lower voltage. It ended with burning up half of my pack because of the lower voltage. Luckily the car itself got saved. After diagnosing the cells and how they where constructed I decided to put that specfic project on hold (but recently picked up thinking about redoing it again).


So yes it can certainly be done, building EV batteries from 18650 cells as per DIY.
But one need to think about proper busbar sizing, protecting module covers/casings, module interconnections etc.
How did the cost of your pack compare to reusing an OEM pack?

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I've seen some videos of a homemade go cart that he made. Will definitely look into this option. Don't I need a Dcdc converter for 12V accessories like lights, switches, and AC?
You will want a DC-DC converter, yes. I'm just wondering how you intend to control the one from the Leaf, as its CAN controlled, right?

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How did the cost of your pack compare to reusing an OEM pack?


That is comparing apples with oranges.
Ofcourse 18650 is much more expensive but gives you all the freedom to design and build the modules as you like them.
Some OEM packs can be very easily disassembled and reconfigured. If that is the only benefit, maybe he should sell his current cells and buy OEM, since building your own is not more economical and may not provide any performance benefit.

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I used leaf batteries and fit an entire pack in a 2000 Miata. Here is my build page https://www.diyelectriccar.com/forums/showthread.php?t=184625

If you have the flexibility of smaller batteries you can fit some in lower than I did in the front and also build a custom box that drops down below where the fuel tank was, there is some room before you get to the differential, although maybe the NA Miata is a bit different. I ended up with about the same weight distribution as stock and don't have any handling problems.
 
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