Electric Porsche 944

A New Direction

by on Sep.28, 2013, under Electric Car

From the start of this build there have been countless changes, and with the exception of the donor car every single component has been revised/updated/eliminated due to testing/learning or simply something new becoming available that just didn’t exist earlier in the build.

I absolutely love the Warp 11HV and Soliton1 together, the torque is incredible and the car does 0-60 in 4.8 seconds.  I absolutely hate the brushes and brush dust in the 11HV.  (And the fact my 11HV requires repair/cleaning)   For this reason I finally have to agree with the OEM’s that some type of brushless motor is required for a daily driven, low maintenance EV.  The series DC motors still have a place right now simply because there are no high power AC systems available to the DIYer at a reasonable price.

When Azure Dynamics went bankrupt last year I picked up a DMOC 645 AC Inverter as well as an AC24LS AC Induction motor.  I never really had a plan for the set, however the AC24LS would never be able to give me the performance I’m looking for in the 944 without burning it up.  The motor that Azure Dynamics paired with the DMOC 645 was the Siemens 1PV5135 4WS14, an abnormally low voltage version of the typical Siemens AC Induction traction motor.  This motor should give me decent performance for daily driving.  I won’t have the 290-300ft-lbs of torque that I got from the 11HV but a more modest 220ft-lbs is still well above what the stock engine could produce.  The Siemens motor also rev’s much higher, there is good power out to 7500rpm, and usable power all the way to 10,000rpm.  I’m not sure how well the stock 944 Turbo transmission would like 10,000rpm on the input shaft, so limiting it to 7500 should keep things safe.

A new motor means a new adapter plate and coupler.  As it turns out the length of the existing adapter plate is pretty close to ideal, I’m going to add a 1/2″ aluminium plate that will adapt from the 11HV bolt pattern to the Siemens bolt pattern.  The Siemens motor is slightly shorter than the Warp so the extra 1/2″ does no harm.  The coupler will be much simpler, smaller and cheaper.  There is a steel coupler available that normally mates either the Siemens motor or a Remy motor to the Borg Warner single speed gearbox used by Azure Dynamics (and others).  This coupler is only $72US, mine is in transit but apparently it’s a good quality coupler.  This is only half of the solution though, I can now mate to the splines on the Siemens motor, however the 944 input shaft uses a different splined shaft.  For this I am using the center portion of a stock 944 Turbo clutch disc.

AC copuler

 

After grinding off the flange that normally attaches to the rest of the clutch I’m left with this small splined piece of steel.

The Siemens side of things is similar though a bit longer.  (image from the Vaxo website, click HERE to see more info from Vaxo)

0000212_300

 

The Siemens coupler is 40mm in diameter, the 944 clutch center is also 40mm in diameter.  I still need a pilot bearing, or to be more precise a piece to align the pilot shaft on the 944 input shaft, it doesn’t need to turn as both shafts will be permanently connected.  I don’t have a lathe, however I’ve been able to get good results using my CNC mill to make round parts.

siemens to 944a

 

Above is the aluminium piece that I milled from flat scrap.  It has a 15.15mm ID hole for the pilot shaft to align.  It has a stepped OD, one size matching the ID of the clutch center and the other matching the ID of the Siemens coupler.  This piece will be used for alignment of the steel sections during welding and remain inside as the pilot “bearing”.  It will also serve as a stop so that the coupler can not work it’s way off of the Siemens motor and along the splined section of the 944 input shaft.

siemens to 944c

 

The two pieces fit together nicely, it’s not quite as precise as could be done on a lathe, it would probably be better if there was a slight interference fit.  One day I’ll get a mini lathe to go along with the CNC mill.

 

siemens to 944d

 

The DMOC 645 also has some challenges, it’s CAN bus controlled meaning you can’t simply attach a throttle and other things to it directly.  There are a number of VCU’s in development from various people.  My favorite is in the final stages of development by Wolftronix.  This is a guy who is very familiar with both electric vehicles as well as Azure Dynamics/Solectria and because of this I believe his product will be the best first generation product out there.  Others will play catch up and likely incorporate some of  the features that come out in his first product.

DMOC adapter

The above image is from the Wolftronix website and I suggest you check it out for more information.

The Siemens motor is also on route, it was purchased from “Steve” thanks Steve!!!  This picture is from his for sale listing and may or may not be the actual motor I’m getting, he had purchased a lot (10?) motors from the Azure Dynamics auction.

1425_18

 

If I didn’t already have a DMOC I likely would have just purchased the pair from Jack at EVTV, I think his combo price is quite fair considering he includes the required cables/connectors to connect the motor/controller as well as the main IO for the DMOC itself.  I would also suspect the connector for the GEVCU will be included when that is available as well.  Jack is also working with various groups on their versions of the GEVCU, I’m sure they will all catch up eventually but the feature set in the first generation Wolftronix is what I believe to be the best solution right now.  Jacks price on a single item is less attractive and I’m not sure if he would include any cables when only buying one piece.

 

Performance:

In some respects this change could be considered an “upgrade” I’ll have a water cooled maintenance free motor with regenerative braking.  Those are all significant pluses!  There is however a negative or “downgrade”.  The peak power of this system is rated at 118kw, the peak power of my Warp 11HV/Soliton1 right now is around 200kw, and could be higher when the remaining CALB cells are installed.  I have no doubt that the system will still provide an exceptional driving experience, but it won’t be a sub 5 second 0-60 car any longer.

Range:

I have more cells to install anyway, so range goes up, with the regenerative braking I will probably get a tiny bit more range.  I live on a bit of a hill so I should be able to recapture some energy on the way down instead of heating up my brakes.  More than anything, my peak power will be lower, which to a certain extent limits the amount of energy I can burn accelerating away from a stop sign or light.  With all of these factors combined I expect my Wh/mile to drop from 300-325 down to 275-300, not a significant difference but still a difference.  The DMOC also has a higher input voltage range, instead of 350v max like the Soliton1 it has a 450v max rating.  It’s nominal cell count is 105 where the Soliton1’s max cell count is 100.

I will have 100 cells once I add in my remaining CALB’s, I also have a few more A123’s that could be installed if I have the room.  Each cell adds around 1km of driving range and I could easily go up to 110 or 115 cells providing I have the space to mount them efficiently, it’s never been an option so I’ve never actually looked into it.

Another small but interesting fact is my 944 will once again have a water cooled german motor.


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