1983 911SC Conversion to Electric Drive

[ElectricPorsche]

Over the last year I've been converting my 1983 911 SC targa to an electric drive. Couple reasons: I've wanted an electric car for 15 years, ever since I drove one. I don't like many of the existing electric or hybrid cars available, and I don't want to pay Tesla prices for what is basically an amazing electric lotus roadster. I love the torque from an electric motor. Clean, quiet, reliable power. Lithium batteries are now at a point where it is feasible to get decent performance.

Here are some pictures from my build:
Having the motor and engine in the same image gives a good sense of scale. I am using a 9 inch diameter motor, the Warp9 from Netgain.

This hub is a taperlock two piece mount for bolting the flywheel to the motor.


Here the flywheel, clutch, and pressure plate are bolted together.


Motor and transmission are connected with a cast aluminum adaptor plate.


The motor is mounted in the car.


Here is the motor controller and liquid cooling loop. The controller is rated for 320 kWatts continuous (453 HP), but my motor will only handle 225 HP peak. I'll start with a limit around 150 HP and see how it goes. This limit is easily configured in the controller.


I am now working on mounting the batteries: 60 lithium cells (Lithium Iron Phosphate), 192 V, 1000 Amps, 34.5 kWh capacity - enought to go 100 miles on a charge and do 0-60 MPH in 7 seconds. I will end up 200 lbs over stock weight.


28 cells will go where the gas tank used to live. The rest of the cells will go in the back. Weight distribution will shift forward 1.5%.


The torque curve of the electric is superior at lower RPM. I will be giving up 20 MPH on the upper end but I rarely exceed 100 MPH anyhow.

[Jim Sims]

I've considered a project like this; keep the progress reports and images coming. Did you remove any of the transmission internal parts?

[SteamWolf]

Interestig that you have kept the gearbox. Most EV's I've seen were all direct drive.
What is the build cost like? Is it worth the expense to save a couple of grand a year in fuel bills?

[ElectricPorsche]

Originally Posted by Jim Sims

I've considered a project like this; keep the progress reports and images coming. Did you remove any of the transmission internal parts?

For the transmission I only replaced the 4 seals and the transmission fluid. I'm working on the battery racks and I will post updates. I have more details in my build blog: Electric Porsche

Originally Posted by SteamWolf

Interestig that you have kept the gearbox. Most EV's I've seen were all direct drive.
What is the build cost like? Is it worth the expense to save a couple of grand a year in fuel bills?

I kept the gearbox because it came with the car and it allows me to use a DC motor. Most direct drive (or fixed gear drive) electrics use AC motors which can spin at higher RPM, with good torque across a wide RMP band. But for torque off the line at 0 rpm, the series wound DC motor is the best. I expect to use 2nd gear up to 45 MPH and 3rd gear at higher speeds. AC motors are expensive for the hobbiest because a lot of the manufacturers only sell to OEM.

A project like this starts at $20,000. I've got a bit more into it because once I got started I couldn't resist getting a bigger battery pack (100 mile range) and a more powerful motor controller. My project is not cost effective because of the high cost of lithium batteries. Payback pencils out to 15 years. I'm buying all my parts at essentially retail price, so a car manufacturer would probably be able to do better. If the battery prices drop, and you could get 300 miles per charge, and refuel in 10 minutes, I feel there would be no technical barrier for electric cars to become viable. I'm doing this project because I love the low end torque of the electric motor, I hate the complexity of gasoline engines, and for 15 years since I first drove an electric vehicle I've wanted one.

[ElectricPorsche]

28 of the 60 cells I purchased will be mounted up front where the gas tank used to live. After designing a layout pattern, I made a plywood template to test the fit.
I used the plywood to layout the base frame. Once the pieces of angle iron are cut to length and clamped down with square corners, the frame is welded together. I oversized the frame by 3/16” (4.75 mm) so that the frame can be lined with a rubber mat.




After the base frame was completed, I made tabs that fit the gas tank mounting locations and tack welded them to the battery rack. Then I made the upper frame of the battery rack. The right front corner of the frame bolts into place and is designed to clamp the batteries securely in place.


Here is the rack populated with 28 cells. There will be a sheet metal base to support the cells, and open sides, as the cells in the trunk are fully protected from road splash. The top will be covered with an acrylic sheet to protect against voltage hazard, but still keep the cells visible - especially important if the car is ever displayed.

[jadewombat]

Great stuff. I converted a '70 VW bus when I was in college in the mid-90s. Quitest, cheapest, cleanest car I ever had.

[Tremelune]

Very, very cool. The key being that you're not losing performance by going to electric. You'll have more torque when you really want it and less horsepower when you don't. I'm surprised the weight distribution wasn't changed more drastically, with less motor and more batteries up front. Is the electric motor that heavy (or is fuel really that heavy)?

In ten years, you'll be able to easily throw some new hotness batteries in there and double your range.

[ElectricPorsche]

The rear battery boxes are nearing completion. There will be 12 cells in each box.



Tremelune, thanks for your post. Originally, I was going to convert a truck, because lead batteries need a sturdy platform to handle 2000 pounds of lead. So these batteries are the hot new batteries I needed for my project!! Once I decided to use lithium and switch to a sports car, I felt it would be a crime to end up with golf cart performance.

But you are correct, if electric cars are to gain market share, battery technology must continue to improve. I think that target goals are 300 miles range, 10 minutes to refuel, and $5,000 price tag.

[ElectricPorsche]

Originally Posted by Tremelune

Very, very cool. The key being that you're not losing performance by going to electric. You'll have more torque when you really want it and less horsepower when you don't. I'm surprised the weight distribution wasn't changed more drastically, with less motor and more batteries up front. Is the electric motor that heavy (or is fuel really that heavy)?

Gas is just over 6 lbs/gallon, so at 20 gallons the tank was about 120 lbs. I'm adding a net 200 lbs to the front.

The motor is 156 lbs. The charger and controller are about 30 lbs each. I got rid of a 400 lb engine, and the net rear gain is about 100 lbs.

So after updating my numbers (I ended up using different batteries from my original plan), it looks like I will be 300 lbs over stock, and the distribution will move forward by 3% (41%/59%). I hope that doesn't mess things up too much. I did take ride height measurements before I started and I may be able to modify the suspension with after market parts if needed.

[Tremelune]

Am I crazy to think it wise to put the batteries ahead of the rear axle? They can pretty much go anywhere on the car and balance will improve significantly if they went where the rear seats are.

[jadewombat]

Originally Posted by Tremelune

Am I crazy to think it wise to put the batteries ahead of the rear axle? They can pretty much go anywhere on the car and balance will improve significantly if they went where the rear seats are.

Yes.

But then you have to construct a firewall inside the car with proper vents. Lithium batteries are pretty lethal when they go bad from rupturing. Stink like hell and give off some nasty gases.

All depends on what the goals for the vehicle are though. If this was an autocross demon, probably wouldn't need so many batteries (maybe 1/3 depending on voltage needs) and yes the best spot would be just behind the fronts seats on the floor to get everything close to the CofG.

[ElectricPorsche]

Originally Posted by jadewombat

But then you have to construct a firewall inside the car with proper vents. Lithium batteries are pretty lethal when they go bad from rupturing. Stink like hell and give off some nasty gases.

All depends on what the goals for the vehicle are though. If this was an autocross demon, probably wouldn't need so many batteries (maybe 1/3 depending on voltage needs) and yes the best spot would be just behind the fronts seats on the floor to get everything close to the CofG.

Correct. This will be a dailly driver. I wanted to maximize range and I didn't want to modify the interior. For more performance, I would use smaller, more powerful lithium polymer batteries, but with less range. I would also double up with 2 motors. My pack is 750 lbs, but many drag racers have packs in the 200-300 lbs range.

[ElectricPorsche]

Only 8 cells left and they will be the most challenging to fit. Along with the last of the cells, I still need to fit the controller, radiator, charger, brake pump, 12 volt battery and DC-DC convertor (for charging the 12 volt battery from the main pack).

[ElectricPorsche]

I cut a plywood template fitted above the motor and lower battery boxes to help layout my components (the plywood will not be permanent). I need to fit the last 8 cells, the controller (on the left), fuses, charger (black finned box on the right), and my water cooling system in the back.


The last battery box is taking shape:

[Aurel]

Very cool project. I have 15 years of R&D in Li-ion cells if you need any advice on other chemistries. And own a 78SC too. LiFePO4 is a good choice for power, safety and cycle-life. But not the highest energy density cathode. Maybe when time comes to replace them, there will be cheap batteries with NCM cathode, or high voltage spinel. Could your controller handle other chemistries? I cannot wait to see the results of your conversion. I am also curious about your old 3.0L engine. What shape was it in? How many miles on it? Are you selling it? (Mine needs a rebuild).

Cheers.

[ElectricPorsche]

Originally Posted by Aurel

Very cool project. I have 15 years of R&D in Li-ion cells if you need any advice on other chemistries. And own a 78SC too. LiFePO4 is a good choice for power, safety and cycle-life. But not the highest energy density cathode. Maybe when time comes to replace them, there will be cheap batteries with NCM cathode, or high voltage spinel. Could your controller handle other chemistries? I cannot wait to see the results of your conversion. I am also curious about your old 3.0L engine. What shape was it in? How many miles on it? Are you selling it? (Mine needs a rebuild).

Cheers.

Thanks. I fully agree that LiFePO4 is a compromise compared to other lithium chemistries, but it is worlds better than lead acid. The safety factor and long cycle life were my main factors for selection. It is true that the price will need to come down (or gas prices go up) before electric will gain significant automotive market share.

The controller will accept up to 340 V, and that is the only controller limit as far as batteries go. The charger is the component that is most sensitive to battery chemistry. The charger uses a constant current, constant voltage profile (CC/CV). With these cells, a resting voltage of 3.38 is considered 100% charged, but it takes a few days rest before you can measure an accurate resting voltage. So it is accepted practice to charge these cells at a constant current until you reach 3.6 V per cell, and then hold the voltage constant until the current drops to a level of C/20 (cell capacity divided by 20). I have 180 Ah cells, so 180/20=9 amps for my cut off). The voltage will settle to 3.38 V using this recipe. Because the main failure mode of these cells (in automotive applications) is due to either overcharging or over discharging, it is a good idea to avoid taking the cells up to 100% charge. I plan to slightly undercharge to maybe a resting voltge of 3.33 V/cell. So any new chemistry may have charging profile implications. I suspect I'm not telling you anything new here and I'd be interested in hearing your take on battery charging.

I still have the motor. I'll be looking to sell it in a few months, after I figure out all of the electrical connections I need trace out through the engine harness (brake and reverse switches to connect to my controller). The motor has 97,000 miles, and ran great. The previous owner gave me service records for the last 10 years. Two known issues - the oil tubes dripped oil onto the muffler and you get some smoke during warm up after sitting overnight (no smoke from the tail pipe itself), and there is a loose muffler bracket that rattled sometimes at idle. The seal at the crank hub may leak. I found a coating of oil in the transmission bellhousing and I'm not sure if it was motor oil or transmission oil.

[ElectricPorsche]

I finished the last battery rack today.

[saxen]

I don't really care for cars like this to be converted- however your fab work and lay out look great- sub'd to see more!!

[ElectricPorsche]

Originally Posted by saxen

I don't really care for cars like this to be converted- however your fab work and lay out look great- sub'd to see more!!

I understand. A guy I work with wouldn't talk to me for three weeks when he found out about this project, he was so angry. That's why I will consider it a failure if I can't beat factory performance. I did consider a reproduction car like the Beck spyder, but the budget just didn't support it.

[jadewombat]

If I have the time and means again someday I'm considering doing a trashed out old Subaru or Evo as an autocross demon. 2 motors, mount one to each diff. directly and the minimum amount of batteries for 4 or 5 runs. Could be interesting.