[TBZ]

Hey all,
I have a mechanical engineering background and a hankering for green things. lol. Also love doing cad designs as well (have a solidworks license at home). So if anyone needs help drawing something, I can do my best to assist you in your design.

Bought a 1985 300zx last year for a new project to challenge myself. Really wanted a wedge shaped car from the 70s-80s era. So like 300zx, Supra, RX7, 944, etc... Landed on 300zx because google "research" showed that the engine itself weighed almost 500 lbs which would give me some wiggle room for a motor, inverter, controller, batteries, etc without blowing up the curb weight of the car too much. Also the digital instruments would be sweeeeeet if I can get them to work with the EV setup.

Anyways, I have a list started of parts for my wishlist to get for the car as I tear it down. Thought I would share that here before I start buying all the wrong parts. Main parts I am looking at are listed below.

Motor: Hyper9 or HVH250
HVH250 seems to have a smaller physical footprint than the Hyper9 which makes it more appealing to me. However I am wondering how I could possibly get up to 700v. Not sure what other motors there are out there or if there are any newer/better ones.
Controller: VCU200 Cascadia
Inverter: Cascadia
Batteries: Would like to go the diy 18650 module route. Batteryhookup has a deal to buy 200 at a time for $360. So my design would be to have 20s10p modules (roughly 380mmx190mm with 72v 31ah 2.27kwh) then have 16 modules in a 4s4p setup (roughly 790mmx790mm with 288v 320ah 36.864kwh) in the back to occupy the fuel tank space and a little of the trunk. At 48 grams x 200 cell module x 16 modules = 48x200x16=153.6kg or 337.92lbs. The battery design is some napkin calculations... haha I may switch the module setup to 2s8p for more capacity but I have not decided yet.

Will add more later... Just got some downtime at work and thought I'd post this.

 

[remy_martian]

4s4p is 288V and 124Ah, isn't it?

Your car is blessed with an IRS...why aren't you putting a complete drive unit (Leaf, Model 3, Tesla SDU, etc) in the back and putting the batteries in the front?

 

[OR-Carl]

Would like to go the diy 18650 module route.

The price per kWh for those cells is not bad, but dont forget to take into account the costs for everything else that you are going to need to make those modules. Building a car-sized pack from 18650s is going to be a massive job. You would want to include a fuse on each one, and depending on the sort of performance you are hoping to have, a coolant system (and or heater) might not be a bad idea. If you can find a used pack from a wrecked EV you can leave all the fiddly work to a highly sophisticated assembly line.

The price for larger prismatic cells keeps falling, and that might be a viable route if you can not find an OEM module that works with your size contraints (although there are a lot of option out there now, so likely something would work).

 

[TBZ]

4s4p is 288V and 124Ah, isn't it?

View attachment 131072

Your car is blessed with an IRS...why aren't you putting a complete drive unit (Leaf, Model 3, Tesla SDU, etc) in the back and putting the batteries in the front?

You are right. I goofed on my numbers.

I want to keep the…or at least a transmission.

And the leaf motor sounds VERY possible after going through the forums some more to see the possibilities. It’s funny you search around and people trying to sell these pre-packed/overpriced deals and then you see what everybody is really doing is so different. Lol. Anyways I actually found some leaf motors for about 580 each on eBay. Quite the discount in comparison to what a hyper9 or hvh250 would cost. Then might go the open inverter route. I think @MattsAwesomeStuff referenced them and evbmw a few times in my searches. Hopefully all of that is still going on seeing the ev86 on YouTube about a month ago.

 

[remy_martian]

Having a motor that revs over 10 grand eliminates the need for more than one ratio, will easily light off the tires when you don't want it to using a DU or reducer, and will be a quicker car from a standing stop.

You'll be much happier with a well balanced car than you ever would be shifting it. Unless you plan to go over 130MPH, or have a beam axle in the back, a second gear ratio or transmission is a waste of mass in an EV.

Your build, your regrets. Do as you wish.

 

[TBZ]

The price per kWh for those cells is not bad, but dont forget to take into account the costs for everything else that you are going to need to make those modules. Building a car-sized pack from 18650s is going to be a massive job. You would want to include a fuse on each one, and depending on the sort of performance you are hoping to have, a coolant system (and or heater) might not be a bad idea. If you can find a used pack from a wrecked EV you can leave all the fiddly work to a highly sophisticated assembly line.

The price for larger prismatic cells keeps falling, and that might be a viable route if you can not find an OEM module that works with your size contraints (although there are a lot of option out there now, so likely something would work).

Well I do a lot of soldering and wiring on pcbs for work. I felt like it would be something I could do for this as well. I think all I really need is a spot welder, the material to tie the batteries together(like you mentioned fuses) and the BMS.

I’ve been thinking of a coolant system as well. Surely there’s some kind of way to have a heat sink without shorting the batteries. I saw something like a conductive foam tape someone used for that reason.

 

[remy_martian]

A wirebonding machine for power devices is not cheap. Spotwelding by hand might work, but is awfully tedious over several thousand cells. You also have to have 6 sigma yields over that many connections.

Some people see their non-working hours as costing nothing. Yes, true for some, but you also could be consulting as an ME during those hours at $300/hr and have a CM do the assembly for you.

It only makes sense to me to do such crazy things if there's some special sauce you can't get from the market already. And if your time's worth nothing to other people.

Tesla and LG chem have already done it all and done it well. Plug n play.

 

[OR-Carl]

I’ve been thinking of a coolant system as well. Surely there’s some kind of way to have a heat sink without shorting the batteries. I saw something like a conductive foam tape someone used for that reason.

Basically if you are going to go the 18650 route, take a look at a battery tear-down video of a Tesla battery pack. That might give you an idea of the reverse engineering that you would need to do. They use a flattened aluminum tube that snakes through all the cells for cooling, which is likely going to be beyond the capabilities of the average DIY garage builder. I remember some guy claiming that he was going to get superior performance from literally "garden variety" black polypipe, but I never did hear how his project worked out. Soft copper tubing like is used for compressors and water supply lines to an ice-maker on a fridge might work well, but would be quite expensive (and fiddly).

You also need to make very sturdy enclosures so your cells dont jump around when you hit a pothole- Tesla used a variety of different plastic trays, and then glues all the cells in place.

Then you will also need to make bus bars that can handle whatever current the module will be able to produce. Each 20s module will need 21 plates, although if you are going to be putting your modules in parallel, you might be better served making the modules with more cells in parallel and having fewer overall.

If this sounds like something you are going to knock out in a weekend, then you are dreaming. It is of course completely doable, but It is going to be a massive undertaking, and will not come close to the precision and robustness of a pack manufactured in a modern assembly plant.

As Remy noted, the only reason to go with an 18650 pack is that you could tailor your pack exactly to your needs. Small cells in theory could be configured to use otherwise unuseable spaces, but dont underestimate how much work this is going to be.