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Discussion Starter #1 (Edited)
Location: San francisco, CA

Budget: Like 15k for the donor car, and hopefully less than 20k for all the conversion parts and any labor costs.

Donor car: 1975 c3 corvette. They're cheap, easy to convert the bumpers back to the wonderful 68-72 chrome bumper design, and have some decent safety equipment upgrades over the early cars. A clean 1975 is like 15k, a clean 1970 is 25k or more, YIKES

also, maybe some race car flair to it, need big rear tires to hold all that torque eh?






Motor: Tesla model S P85 large rear drive unit OR Tesla model 3 performance rear drive unit. The entire tesla rear subframe and all the suspension components, fabricating mounts so it bolts onto the c3 ladder frame. This could be relatively easy or the hardest, most expensive part of the entire project. The motor 3 motor is more efficient when not under heavy load, and FAR FAR better cooling capacity BUT nobody supports their firmware yet and it isn't clear how many years it'll be until the T-1C supports it.




Battery: 34kw of chevy volt batteries. I'd like Gen2 but the Gen1s are half the price and only slightly lower capacity. Some in the engine bay with a battery enclosure to make it look like a V8 because yummy under hood candy, like ICON's derelict mercury EV did. the rest of the batteries go where the gas tank used to be, which may or may not hang lower and thus cause the full size spire tire sling to have to go away. Volt batteries have excellent high performance because of almost no voltage sag. They're also cheap, work very reliably, have a nice log-like form factor, and have built in excellent battery cooling. I'm hoping for 80+ miles of range




Cooling: unsure yet, but the water pump and electrically controller diverter valve out of a tesla. chevy volt batteries and the tesla motors have built in cooling systems so no need to screw around making chill plates.

Controller: EV Controls T-1C, pretty close to turn-key, i'd buy it from EV west specifically so i can lean on them for tech support and general info. This controller's already been used in a few tesla motor/chevy volt battery builds



Contactor: unsure

Power steering: I really want to keep hydraulic power steering, electric pump driven. It's wasteful but it feels so much better than electric power steering. EV West makes a belt fed pump but i'll probably re-use the one that came with the car.

A/C: MVP might omit this since i live in a SF and A/C is kinda unnecessary

Charger: Not sure how to get there, but i absolutely want to shoot for a 50kw charger which interfaces with CCS. With such a short range this feels like a heavy requirement for this to be driveable. There's some noises about CCS charging for DIY builds but this might be a wait and see, hopefully this becomes a mature thing soon (within a year). For 50kw, maybe just stack 5 of those 10kw tesla chargers...?

Safety: Haven't researched much but i would really like switchable fuses between every 72 volts or so, so at any given moment during assembly or maintenance, if i make an oopsie, i only get shocked with 72v before a fuse cuts it. Also, inertial fuses so in a crash, everything is isolated from everything else. Also, a first responder safety line, mimicking tesla's implementation with a BRIGHT RED WIRE right under the hood with a really obvious label on it.



Timeline: purchase the c3 within a few months, spend about a year maintaining it, adding quality of life upgrades, more deeply researching the platform, more deeply researching the feasibility of my componentry and fabrication. HOPEFULLY buy most of the drivetrain bits in advance and make sure the entire thing works on a bench, THEN start converting in fall of 2020 and be done some point before fall of 2021


So, what am i missing, what bad assumptions or assessments am i making, etc
 

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Discussion Starter #3
hmm, what would you say is more reasonable for the ev bits if not 20k?
i guess, on the upside, i can sell the engine and transmission and exhaust/fuel system/tank to a good home to make a couple grand back
 

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The Tesla Model S/X drive unit places the motor behind the axle, and that's where the fuel tank is. This could be a packaging challenge, depending on the orientation of the battery modules. The overall plan seems workable, but a realistic look at how everything would go together would be required.
 

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Discussion Starter #5 (Edited)
The Tesla Model S/X drive unit places the motor behind the axle, and that's where the fuel tank is. This could be a packaging challenge, depending on the orientation of the battery modules. The overall plan seems workable, but a realistic look at how everything would go together would be required.
i actually get a little lucky with this, the gas tank sits on top of the frame rails and the motor will be entirely under the rails, in a similar location to the stock diff although hanging out the back more







also, i did some rather rough fitment approximation using a c3 frame cad file i found somewhere, and a model s subframe i found somewhere else

the orange shaft is where i think the center of the axels are when the car's sitting on the ground






 

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i actually get a little lucky with this, the gas tank sits on top of the frame rails ...
Right - I forgot about that detail from the last C3 discussion. It would be good to put a module under that tank level - mass up high is bad.
 

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Are you sure you have enough room for two full Volt packs? I love those batteries, I have most of one pack in my car, but they are bulky and heavy compared to Telsa modules. Two full Volt packs will run 720-ish pounds. A little shy of twice as much as equivalent Tesla modules. Volumetrics are similar.
 

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Discussion Starter #8 (Edited)
Are you sure you have enough room for two full Volt packs? I love those batteries, I have most of one pack in my car, but they are bulky and heavy compared to Telsa modules. Two full Volt packs will run 720-ish pounds. A little shy of twice as much as equivalent Tesla modules. Volumetrics are similar.
think so, did some quick and dirty cad work and the vast majority of the two packs can fit under the hood as a fake V8, with another long module or two going down the transmission tunnel since there's room, then a final 2 or 3x short modules taking up the gas tank
if i have to (hopefully i won't), i can consume some of the letter box "trunk" space with another module or two

by comparison, a big block chevy engine with all the fixins is like 600 pounds, not including exhaust headers and such, so 600 pounds of batteries in the engine bay is within expected bounds for mass, the th400 transmission is like 135 pounds which is another module or two, and a fully loaded 20 gal gas tank is 121 pound of mass plus the a few pounds in the weight of the tank itself.
 

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I like your approach to research and detail. Please keep posting here to show off your progress.

I've always wanted a C3 Vette, and I've liked the idea of doing an EV conversion of one for years. But instead I cheaped out and went with a poor man's Vette, the Opel GT. (If you're curious, thread here: https://www.diyelectriccar.com/forums/showthread.php?p=1046563 ). I'll be watching your build vicariously as the higher-budget higher-class upgrade I kinda wanted to do instead.

...

I think it's prudent to not be overly prescriptive of what you necessarily want, unless you're passionate about certain build details. Rather, figure what you want for performance, and then fill back on the stuff that can make that happen. You might be doing that, I'm not sure, just a general warning that you don't put the cart before the horse because maybe you'd be happier doing things a different way.

Donor: Love it.

Budget: $35k is enough to give you some options.

Motor: I have a feeling you're kind of set on something this powerful, or that you'd rather not bother. So, that's cool, you can make this work and your layout seems to work for the powertrain. Budget will be eaten significantly, but, it's a good foundation for the rest of the build.

Batteries: You're going with the most expensive drivetrain, and the cheapest batteries. There is nothing wrong with Volt batteries, except that they're overbuilt. That is, they are bulky and heavy for their energy density. That's going to hurt performance and range. They are cheap though. It's really the only other way to keep your budget down though, as it's usually the single most expensive component.

You're better off with Volt packs than, say, Leaf packs. But unless you're finding something less popular, Volt and Tesla are kind of the two options for you, and you might not be able to afford Tesla.

Battery prices for salvaged OEM packs may continue to fall in the future, so, if you're planning on being done in 2 years, you might want to hold off and just make the purchase later. Some of us (me, I think) kinda talked too much about how great Volt packs are for off-grid storage and their prices are double what they were a year ago, but generally I think other packs should become cheaper. You could even design for a specific form factor and just make the purchase last minute.

Cooling: Generally cooling is nearly a non-issue, and can be solved by just about anything. A half-assed plan is fine, you'll just "do something" when the time is right, and it'll take a bit longer than you hoped, but, not a lot to worry about.

Controller: The drive unit for the tesla comes with a controller of sorts. You might as well use it rather than spend $3500 on another controller. I think Damien (EVBMW.com) has a kit you can build yourself that can control Tesla drivetrains.

Contactor: Anything, solve it when you solve it.

Power steering: Re-using one but electrically powering the hydraulics is fine.

A/C: You could just plumb one from another EV, but, it's not essential to the car working, so, maybe plan for it space-wise but otherwise upgrade it when you want it.

Charger: You might have to scale back your expectations on how fast you can charge on the road.

Safety: Safety line is a good idea. Your battery pack fuses, sure.
 

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Discussion Starter #10 (Edited)
I definitely could go the more bespoke route like what Damien did but i'm specifically looking for more turn-key stuff to reduce the unknowns and more importantly, get tech support for if things go weird

drivetrain wise, i'm going for the model S rear + 34kw volt batteries because it's been proving in multiple projects by now, i really like things that have been done before because it becomes a solved problem with fewer unknowns.

priority wise: Horsepower, handling, fast charging, and simplicity of components. That means range isn't important, lower weight is a priority, and being able to push tons of amps consistently is important. Volt packs sort of fall out naturally from those requirements. As for the tesla motor, i just find it'd be more livable vs the old school warp DC builds, also more aftermarket support both now and in the future. There's a reason EV west is changing some of their kits over to a tesla small drive unit architecture instead of the siemens motors.

Model 3 motor would be better but...well....nobody is supporting that yet, and even if they supported it a year from now it'll be a while before it's proven.

also the volt price per kilowatt is crazy cheap. I can get 34kw for like, 4 grand at the most. 34kw of tesla packs. Even if i can get full packs for $1000 a piece, that's still $7000 for 7 tesla packs (37.1 kw)

And wiring up 37kw of tesla packs in order to get 350-400v nominal, that's a lot of S and not a lot of P, voltage saaaaaaag



examples of what 34kw of volt packs + p85 rear can is able to do:
this 818 uses the T-1C controller, it's their shop car
https://www.youtube.com/watch?v=F6ITzRiAUTg




blue lightning uses a more traditional ECU by motec with a ton of custom software fiddling to make it into an ev management system
https://www.youtube.com/watch?v=t3F-8QnmNW0


I'm waffling on adapting the model s subframe over though, it may be much less fab work to just weld motor mounts to the cross members around where the diff is in the stock c3 frame, the motor might need to sit at a weird angle though, sort of cocked upwards in the back.
Problem is, the leaf spring in the stock c3 uses the diff itself as a central suspension member! Not sure how to adapt that to the model S motor?
 

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To Matt's point about waiting for a while

The Volt packs are now a limited resource - they stopped making the Volt a while back

If you wait 2 years they may well be unobtainable!

Two parts to that - future proofing - and price
Is something else going to "replace" the Volt packs?

How many Chevy Bolts are being sold??
 

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Discussion Starter #12
If that's a factor i'd look at the packs used in the VW architectures, personally, because they're pretty good and will be EVERYWHERE soon
the two BIG problems with those are
1) unknown platform, like, haven't been used in a lot of conversions
2) no built in cooling so i have to machine a lot of chill plates and design my battery boxe(s) around those chill plates.

those are both huge mitigating factors imo, unless chill plate fab/positioning isn't as big of a problem as i thought
 

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Hi
As far as I know only the Nissan Leaf does NOT have liquid cooling - I'm pretty sure the new VW's will have liquid cooling
 

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Discussion Starter #14
correct, they will have liquid cooling in the car
but if you separate out the modules, they do not have liquid cooling built into them. the Volt and tesla packs have cooling chill plates essentially baked into their form factor



see, this chevy Bolt battery pack disassembly video, the chill plate is designed to fit in that big pack but it doesn't split apart into smaller chill plates
https://youtu.be/ssU2mjiNi_Q?t=5348

the battery modules themselves:
https://youtu.be/ssU2mjiNi_Q?t=4058

so, if you want cooling, you'll have to make your own chill plates :/
 

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Flat coolant plates are easy to make

I made one for my controller - all you need is a thick aluminium plate and drill some long holes with liquid connectors

The actual Chevy ones will be lighter and cheaper for them to make - but we can easily make something that does that job
 

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Discussion Starter #17 (Edited)
Flat coolant plates are easy to make

I made one for my controller - all you need is a thick aluminium plate and drill some long holes with liquid connectors

The actual Chevy ones will be lighter and cheaper for them to make - but we can easily make something that does that job
the plates are easy but you have to design your entire battery box architecture around including those chill plates in the right locations, and bolting the batteries to them in the right orientation etc.
with the volt packs it's just like, line em up and plug your coolant lines into the coolant ports on em

also, i literally can't find a chevy bolt battery module for sale, not even car-part has them yet
 

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Problem is, the leaf spring in the stock c3 uses the diff itself as a central suspension member! Not sure how to adapt that to the model S motor?
I assume that you're referring to the use of the final drive (diff) case as structure. Some sort of framework could probably be built, but most people would probably just do a conversion from the leaf spring to coils (coil-over shocks).

A bigger problems is the use of the axle shafts as suspension links (which has nothing to do with the leaf spring), so the final drive (diff) output bearings need to handle lateral forces (cornering loads) as pushing and pulling on the axle shafts. The solution is to not use C3 suspension... it's just hopelessly antiquated, and incompatible with any modern drive hardware. On the other hand, apparently swing-axle Triumph Spitfires have used Hitachi (used by Nissan and Subaru) diffs without destroying them... so some sort of hack might be possible.

If you don't want to use the Tesla suspension and subframe, an option would be the C5 components on a custom subframe; the Tesla powered Mercedes Vito shows this is possible with a large Tesla drive unit.
 

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As far as I know only the Nissan Leaf does NOT have liquid cooling...
There have been others, but the Leaf is the only common modern EV without liquid cooling, and the only one without active cooling (there have been some with forced air).

the Volt and tesla packs have cooling chill plates essentially baked into their form factor
Yes, and they're the only ones as far as I know. Even Rivian's pack design for their proposed pickup and SUV use plates under the modules... and they even use cylindrical cells like Tesla.

Rivian does bring an interesting idea: apparently they are sandwiching chill plates with modules on the top and bottom of the plates, getting double use out of each plate and eliminating a large unused face. Of course that make the packaging challenges worse, especially since the plate must go on one specific face of the module.

And we shouldn't call them "chill" plates, because they heat the battery under some conditions.
 

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Is something else going to "replace" the Volt packs?
I think that's a good question. The Bolt seems obvious, but has the same problem as other mainstream EVs: with 60 kWh pack capacity and the modules all in series, using a fraction of the pack which fits in a conversion means getting a fraction of the operating voltage. That might work out well for brushed DC motors and aftermarket motors intended for industrial vehicles (e.g. the HPEVS AC series), but is a concern for salvaged EV motors that are designed for the voltage of a full 96S pack.

Some people are starting to use the LG Chem modules from the Chrysler Pacifica Hybrid. Like the Volt, the modules total 96S but are only ~16 kWh in total, since (like the Volt) it is a plug-in hybrid. Logically the Mitsubishi Outlander PHEV would be a similar source, but I don't know if those will ever be common.
 
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