# 944 Tesla Conversion



## mfor1000 (Aug 22, 2017)

I'm starting my first EV project...so be gentle.

Here is what I have so far:

1987 Porsche 944
Tesla Large Drive Unit (Thanks @WK057! and HSRmotors.com)
2x Chevy Volt Battery (second on the way)
Tesla 2nd Gen Charger 

Fitting the drive unit to this car should be pretty straight-forward. It has a semi-trailing arm rear suspension and had room for a transaxle. Once I remove the transaxle, fuel tank, and exhaust, it looks like there is plenty of room. (see pics) For half shafts, I plan to weld a flange to the inner cups from the Tesla shafts to allow the use of the stock 944 CV's.(similar to @jackbauer's Panzer project)

The plan for the battery is to widen the transmission tunnel on the car and sacrifice the back seat for the first battery. Then build a box for the engine bay for the second.

I will definitely use a BMS system for the batteries. I'm hoping @bigmouse can help me with that. It looks like he has that figured out for the Volt BMS. 

I'm still debating on controlling the charger. It looks like my choices are the custom board by @jackbauer and the upcoming controller from @WK057. 

I haven't bought a DC converter yet...looking for suggestions there.

Please feel free to tell me when I'm screwing something up. I'm going to try to keep this up to benefit from everyone's advice!


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## Duncan (Dec 8, 2008)

Are you going to disassemble the Volt batteries and use the modules?
Trying to use the complete T shaped units ....

When you take the modules off the bottom plate you can then drill out the spot welds and use the mounting hardware without the heavy bottom plate


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## mfor1000 (Aug 22, 2017)

Unfortunately, the suspension lateral tube prevents keeping the T completely intact. I'll have to split it at the T. 

The longitudinal tunnel portion of the pack will go into the widened trans tunnel, while the lateral T section will have to reside above that suspension tube in a box created where the rear seats currently are. 

The plan is to split it and then use longer hoses and wires to connect the two parts of the pack. I also am going to attempt to retain the fiberglass cover by splitting it as well and then glassing in sections to seal the holes.

I'm currently try to read the voltages from the BMS in CAN...struggling a bit. A friend did see a post on this:

http://www.diyelectriccar.com/forum...ting-hack-chevy-volt-drivetrain-107946p6.html

However, the voltages from that are not making sense.


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## Duncan (Dec 8, 2008)

Hi
Unless the T dimensions fit with your space (lucky) I would advice using the modules to alter the dimensions to fit better

Taking the battery apart into it's modules is easy! - and they can then be configured the best way for your car


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## itchyback (May 28, 2014)

this is going to be a sweet conversion!
looking forward to updates


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## mfor1000 (Aug 22, 2017)

I think it will work out ok to break it into just two pieces. Then they well be nice and protected inside the fiberglass housings. The question is whether or not I can widen the tunnel enough to fit over the whole thing and still have enough room for the seats. I believe it will work with the stock seats. I have some racing seats in there right now, which would be too wide.

I'll definitely have to break up the second pack to go in the engine bay. 

I finally figured out what I was doing wrong with reading the BMS. It looks like it is big-endian...(backwards). I attached my Arduino code to do this. It is using a CanDue with Collin's libraries.

Now I get decent numbers. Attached is a screen shot from this code. You'll notice that a bank of cells reads zero and the min is messed up because I found one cell that was a bit low. I unplugged that bank and confirmed it with the volt meter. It was 3.85 volts compared to 3.90-3.91 for all the rest of them. The screen shot was taken with that plug out.

I'm charging that cell now by itself with my trusty drone battery charger set on 1S...a little scary...but slow charge at 0.7 A.


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## electro wrks (Mar 5, 2012)

mfor1000 said:


> Unfortunately, the suspension lateral tube prevents keeping the T completely intact. I'll have to split it at the T.
> 
> The longitudinal tunnel portion of the pack will go into the widened trans tunnel, while the lateral T section will have to reside above that suspension tube in a box created where the rear seats currently are.
> 
> ...


Could you show a picture of the interfering lateral tube?


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## mfor1000 (Aug 22, 2017)

Basically, the T part of the pack will have to sit above this tube and high enough that the suspension doesn't hit it. That is the torque tube for the torsion bars. The rear seats are right above that.


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## electro wrks (Mar 5, 2012)

All right, I see a version of it in this photo: http://bestautophoto.com/imgs/4306-..._post_4306_tuning-porsche-944-25-turbo-03.jpg

And this one: https://newhillgarage.files.wordpress.com/2013/06/dscn0117.jpg

Looks like it has torsion springs in the tube? And coil overs? The coil overs I saw must be auxiliary springs. Thank you.


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## mfor1000 (Aug 22, 2017)

Mine doesn't have coil overs on the rear. It just has the torsion bars and shocks. 

Some racing guys take the torsion bars out and substitute coil overs for adjust-ability I think. I may end up doing that, but for now I'll just try to use the bars.


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## mfor1000 (Aug 22, 2017)

Excuse me if a similar post shows up twice...I sent one earlier like this but it didn't show up. I wasn't sure if I messed something up or if it needed approval.

I figured out my issue with reading the CAN from the Chevy Volt BMS. It turns out to be big-endian, instead of little-endian... That confused me for a while, but I finally figured out the bit shifting and masking to get it right. 

Attached is a screenshot of the output. You'll notice one group is zero and my min is messed up. I found one cell that was at 3.85 V instead of 3.90 V like the rest of them. I unplugged that group and was charging that cell while taking this screenshot. The trusty drone battery charger comes in handy...0.7 A really slow charge!

I also included my arduino code. I'm using the CanDue with Collin's libraries.


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## mfor1000 (Aug 22, 2017)

*Progress! Motor is turning...*

Using the controller from HSR Motors, it is turning in my shop! Jason did test it in his shop first, but this is with my little mockup dashboard.

https://www.youtube.com/watch?v=zhv7QqqKDzA

I'm still working on the software, but have been able to interface with both the HSR controller and the BMS using the two can channels on the CanDue. I'll go ahead and post the latest code as well.

The HSR controller can use 12V in from a momentary switch for each drive mode. So I did that and I then use the CanDue to light up the appropriate LED on the switch once the drive unit has accepted the gear request.


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## chrishazell (Oct 29, 2017)

Regarding your half shafts I would not weld cups on there hardened steel and don’t weld well. With the torque the large drive unit can output I think they will shear off. I am currently working with a company that are going to scan the tesla drive shaft splines and will then be able to make up shafts that use the tesla inner joint and will be able to put whatever spline on the other end to fit to any outer cv joint. I will be using them on Kevin split screen conversion and my 350z conversions should have something end of January so will update you once I get them sorted. 


Sent from my iPhone using Tapatalk


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## mfor1000 (Aug 22, 2017)

Chris,

That does sound interesting. Definitely keep me posted.


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## mfor1000 (Aug 22, 2017)

*More Can Decoded...*

I decoded all but just a couple utility channels on the HSR controller and worked on the Volt BMS some more. 

For the Volt BMS I've been using the following for reference:

http://www.diyelectriccar.com/forum...ting-hack-chevy-volt-drivetrain-107946p6.html

The 0x210 didn't seem to match completely.

The voltage in the first 12 bits worked ok (Big Endian), but the current didn't match up well. I played around and found that bits 3 and 4 combined to a signed 16 bit that when divided by -50 gave similar amperage to what I saw on a clamp meter.

Here is the code I used:

case 0x210: // Pack Voltage, Main Pack Amps
BMS1_packVolts = (((incoming.data.bytes[0] << 8) | incoming.data.bytes[1]) >> 4) / 8.0; // Volts
BMS1_packAmps = ((int16_t)((incoming.data.bytes[3] << 8) | incoming.data.bytes[4])) / -50.0; // Amps

0x264 and 0x304 didn't seem to do anything, but they may need the charger. 

Attached is the full code I'm using for both the HSR controller and the Chevy Volt BMS.


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## Boxster-warp (Jun 22, 2014)

Hello
Why you don't use the tesla modules?
Is there not enough place in the 944?
Greetings Boxster-warp


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## mfor1000 (Aug 22, 2017)

Tesla modules are very expensive, and you need 16 of them to support this motor since they have such a low 'C' rating. I don't have to have that much range. I also don't think it is a great idea to spend a ton on batteries right now. Electric car production is increasing rapidly and the prices of the salvage battery packs are likely to drop quickly in the future. 

My thought is to get the car running with a couple Volt packs and then see what happens. If I can get 5 years out of these packs, then I'll consider upgrading to whatever is the best deal at that time.


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## Kevin Sharpe (Jul 4, 2011)

mfor1000 said:


> Tesla modules are very expensive, and you need 16 of them to support this motor since they have such a low 'C' rating.


The Tesla open source controller allows you to use a lower system voltage. iirc Damien is using 11 modules (250V Nominal) in the BMW 8 Series conversion and I'm using 14 modules (320V Nominal) in the VW Bus.


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## Duncan (Dec 8, 2008)

Re - "C" ratings and voltages

I believe an AC system and a DC system are similar in that the motor/controller are - Power In = Power out devices

So you will start off with a high motor current but a LOW battery current and only as speed/revs rise will the battery current rise

This means that you don't need as high a "C" rating as you might think

On my car I have a 1200 amp setting on the controller - worse case (for me) is the drag strip

My battery current will start out down below 100 amps - it will rise as I accelerate to about 1200 amps (100% controller) and then drop as I continue to accelerate and my motors increasing Back EMF reduces the current - I think it's down at about 600 Amps at the end of the 1/8th when I lift off

This means that I have not (yet) blown the standard Chevy Volt fuse! and my batteries don't seem too unhappy

Theoretically I'm pulling about 20C - but that is only for a second or two


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## rwaudio (May 22, 2008)

Very nice, that's exactly what I'd like to transplant into my 944, the Siemens/DMOC combo is reliable, but lacks power. You may find useful info in my blog related to either the 944 or volt packs. http://www.electricporsche.ca

As for the volt packs, I won't work so hard to keep the whole T with fibreglass shells, just a huge waste of space. I did two volt packs in a Porsche 914 cramming them in every space I could find, while keeping the liquid heating/cooling. 

And just an FYI, the front of the volt module has built in precharge resistors, you could use those instead of the giant ebay one. There are also a couple of contactors and a heater you may choose to use along with some small high voltage relays good for heaters or dc/dc converters, plus some fuses etc.

Good luck!


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## mfor1000 (Aug 22, 2017)

Thanks guys. Yeah, I wasn't planning to use that resistor for anything but mockup in the garage, however, the thought did cross my mind to put it some place prominent in the car just for humor... 

I'm definitely going to take advantage of some of the other parts of the Volt packs. I just picked up my second pack. Everything checked out ok on it so far.

I also think I've found the coolant in and out temperature messages in the CAN stream from the BMS. I was just logging some data and playing with the heat gun. It looks like it is in 0x460. Here is the code I wrote to get it in the ballpark:

case 0x460: // Inlet and outlet temps
BMS1_inletTemp = (int8_t)(incoming.data.bytes[1]) / 8.0 + 20; // C
BMS1_outletTemp = (int8_t)(incoming.data.bytes[3]) / 8.0 + 20; // C
break; 

I'll still need to do a full calibration on it to dial in the gain and offset. These values were just a guess. I'm thinking I'll heat up some water and circulate it with some thermocouples to sort it out.


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## mfor1000 (Aug 22, 2017)

I disassembled the packs today and put them in the general layout. It's going to be a challenge to get them all in.

Right now, I think I'm going to join the three center packs together. They will go all the way through the tunnel and up to the front cross member. 

Are there any issues with joining a pack and making it that long? It will be about 74" long. I'm a bit worried about how to pick it up and support it. Anyone have experience with that?

Thanks...


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## Duncan (Dec 8, 2008)

My tuppence worth

If you look at the base plate you will see the mounting strips - these are attached by spot welds (lots and lots of spot welds)

I drilled out the spot welds and then used the mounting strips and some 20 x 20 steel tubing to make my own mounting frame

http://www.diyelectriccar.com/forum...dubious-device-44370p11.html?highlight=duncan

My frame was only about 5kg! - but it goes inside the car so I have a steel floor under it


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## mfor1000 (Aug 22, 2017)

*Tunnel Pack Cover*

I made some progress on the tunnel pack and housing.

I combined the two tunnel battery modules to save some space. The upper bands for the two modules were welded together to make one big band to go around the whole pack. I bought some 2 meter m6 threaded rod from Mcmaster Carr to bolt the new longer module together. 

For the housing, I want it to be waterproof. I decided to Siamese two tunnel housings together to get rid of the T and have sealed bulkheads at both ends. 

First I cut the front part of the tunnel off two lower plates and welded them together. I did have to drill the spot welds and flip one mounting rail since it is asymmetric. 

I then did the same thing with the fiberglass cover. I fiberglassed that back together. I did 4 layers on the outside and one layer on the inside of woven glass with regular polyester resin.

I plan to reuse the aluminum bulkheads on both ends and make block-offs for the unused connector holes. This should be pretty water tight and protect the pack well. It will also add a ton of structure to the tunnel on the car by essentially turning it into a tube. This will be a good idea since this conversion is going to add so much weight to the car.

All this and it only required one trip to urgent care...didn't get my shield down fast enough when I was grinding once and managed to get a metal shard stuck in my cornea... It was really fun having the doctor pick it out with a needle... Fortunately, no permanent damage...just an irritated eye for a couple days...


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## mfor1000 (Aug 22, 2017)

*Rear Housing Ideas and more parts!*

I got some more presents today. 4/0 welding cable and a pyro fuse. 

I've started work on the rear housing. I'm planning to use the 'T' part from the original housing. I think I'll make a bulkhead from some folded sheet metal and then fiberglass in the difference to make it waterproof with a foam seal like the original. 

For connectors, I ordered some Leviton Series 16 connectors to check out. They are rated to 400 amps continuous, but should handle much more for a few seconds as needed by a big blast. They also have good bulkhead options and many color/gender options that should allow me to make it fairly idiot proof (I need that!).


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## electro wrks (Mar 5, 2012)

*Re: Rear Housing Ideas and more parts!*



mfor1000 said:


> I got some more presents today. 4/0 welding cable and a pyro fuse.
> 
> I've started work on the rear housing. I'm planning to use the 'T' part from the original housing. I think I'll make a bulkhead from some folded sheet metal and then fiberglass in the difference to make it waterproof with a foam seal like the original.
> 
> For connectors, I ordered some Leviton Series 16 connectors to check out. They are rated to 400 amps continuous, but should handle much more for a few seconds as needed by a big blast. They also have good bulkhead options and many color/gender options that should allow me to make it fairly idiot proof (I need that!).


Good find on these connectors. Although the ones I found were only rated for MAX 250VDC:https://jbn-duraline.com/e1016-series-16-series-cam-type-connectors/
Did you find some higher rated ones?


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## mfor1000 (Aug 22, 2017)

The Leviton ones are rated to 600 Volts from what I can tell.

http://www.leviton.com/en/products/16D37-U


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## piotrsko (Dec 9, 2007)

I wonder how big a coolant pump you are going to need on the long stack to get decent flows.


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## mfor1000 (Aug 22, 2017)

Good question about the coolant flow. Since it is a header type system, my first thought is to have the pump push water in between the two packs with a T on one side to get equal flow to each pack.

I haven’t decided on the pump size. I imagine an intercooler water pump would be enough, but I’m not sure about that. 

Does anyone out there have experience with cooling two Volt packs?


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## mfor1000 (Aug 22, 2017)

Just received the Leviton Series 16 bulkhead connector. This sucker is big! It will be a challenge to package. Here it is next to the volt battery connector that I pulled out of one of the bulkheads.


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## electro wrks (Mar 5, 2012)

Yes, and the plugs are almost 7" long! :https://www.powerdistributiononline...p-cam-type-16-series-female-inline-connector/

Too big for my space.


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## Duncan (Dec 8, 2008)

What's wrong with the Chevy ones?
I started off using them until I needed to go to bigger contactors 
As far as the cooling pump is required I believe that it's only needed for the Arizona Desert and to make sure that the temperatures are the same
I use a small solar heating water pump - and I use the batteries to cool my controller
Anything that will ensure that you get a bit of flow will do fine 

Filling the batteries is a bit more difficult - getting the air out! 
You either need a vacuum pump or to put the battery on end to fill


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## mfor1000 (Aug 22, 2017)

My concern with the stock Chevy Volt connectors is the voltage drop and heat when pulling the amps necessary for the Tesla motor. Chevy most likely sized those connectors for their motor. Maybe it's overkill, but these Leviton connectors seemed the most reasonably priced alternatives that could handle the amperage.

I wondered about filling the batteries since the channels are higher than the manifolds on the sides. Thanks for the heads up! 

So it is safe to pull a vacuum on them? I'd hate to collapse those channels. I do have a vacuum pump and an epoxy trap that could be used for this. 

How does Chevy fill them?

I made some progress on the rear battery enclosure. I fiberglassed in the waterfall to use a smaller bulkhead. I'm cutting down a Volt bulkhead to fit. I have a friend at work who is good at aluminum welding.


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## mfor1000 (Aug 22, 2017)

The small bulkhead is back from welding. I also drew up what I'm thinking for the high voltage wiring and connectors.


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## mfor1000 (Aug 22, 2017)

I made some progress on the tunnel bulkheads. A friend of mine welded up some of the stock ports I didn't want to use. The two top ones I filled with silicone and aluminum taped over them. I may use them later and wanted to keep that option open. 

I chose some waterproof passthroughs for the big wires. Then there is a smaller one for the BMS wiring.

I'm planning to use the coolant ports that go with the stock bulkheads. I'm modifying the ports to use standard barbs instead of the OEM o-ring fittings. I found some weld bungs that when turned down fit nicely into the ports. Again, my aluminum welding friend will save the day by melting them together.


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## mfor1000 (Aug 22, 2017)

*New Opportunity*

Recently a roller '79 911 SC showed up on craigslist. I need to fix some rust on it, but I think it will make a better conversion than the 944. It has more room (surprising since it is a smaller car). I also won't need to take a perfectly good 944 apart...this was bothering me.

I also ordered a 74 RSR body kit for it, so I can get some big tires on the back to take all that Tesla Torque. 

Attached are pics of the car and the way it will hopefully look after installation of the body kit...minus the race car livery...

Since this changes the title, I created a new Thread:

http://www.diyelectriccar.com/forums/showthread.php/911-rsr-tesla-motor-192602.html


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