Electric Porsche 944

Archive for September, 2013

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)



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.



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.



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.


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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It may be one of the hottest days of the year but I have heat!!

by on Sep.01, 2013, under Electric Car

I’ve had a bunch of posts over the years talking about heaters, some of them were planning, some were installing, some were testing, some were blowing up heaters.  I’ve finally planned, installed and tested what I hope to be the final version of my 944 heating system.  Surplus components from Think EV’s when they switched from the Mes-Dea RM3 fluid heaters to a ceramic or other PTC heater.  The combo includes a 200-450v RM3 heater along with a high quality bosch pump.  During the removal at Think the HV power wires had been trimmed rather short.  These wires were replaced in a previous post, ready for installation.

4kw heater 3


New wires above, heater installed below.


Like most other systems in the car, it’s very important to me to retain the stock look/feel/function of the original Porsche system.  I’ve talked about it before, but a big thing for me was to NOT have a dedicated non factory switch to turn on the heater.  Some people have an aftermarket switch with some sort of label saying “heater”, this just doesn’t do it for me.  In the stock heating system there is a temperature dial, it’s blue on one end, red on the other, and has numerical values in between.  The most intuitive method of turning on the heat would be to turn this knob from blue to red or some value between, we can all figure this out if we get into a new vehicle that we’ve never driven before.  Why should it be any different in my EV?  In addition to simple operation I also wanted to maintain the “automatic” climate controls that Porsche was using in 1986.  It’s a simple system, it’s mainly vacuum operated based on some simple analog electronics.  To make this happen I installed two microswitches, one in the heater control itself, it’s basically a NC (normally closed) switch that only activates (opens) in the cold position on the temperature dial.  The second switch was installed on the vacuum operated coolant valve that would normally restrict the flow of coolant from the engine.  I don’t actually use this valve to restrict coolant flow, but the microswitch serves to turn off the heater.



The vacuum valve with added micro switch, and installed view below.


vacuum switch

I haven’t found a good program to create schematics but the system is quite simple:

Switched ignition +12v is connected to the NC microswitch on the temperature dial.  In any position above blue (cold) this switch applies power to a 12v relay which turns on the pump that circulates roughly 2L of coolant through the 4kW heater and stock heater core.  The same 12v out of the relay that powers the pump then goes to the 2nd microswitch connected to the vacuum valve that would normally limit coolant flow.  If the cabin temperature is lower than the temperature setting on the dial the valve is open and the NC microswitch applies power to the 12v terminal on the heater.  If the cabin temperature rises above the preset value the vacuum valve closes turning off the switch and removing 12v power to the heater.  The heater itself also has built in thermal limits that attempts to heat the coolant to 70 degrees celsius.  Any of these various systems will turn off the heater which should reduce the amount of power wasted creating excess heat and allow me to dial in the amount of heat I need or want while driving.

coolant tank

With a 4000watt heater the draw on the main pack is 12-13A while it’s “on”.  Only time will tell as to what kind of duty cycle I will end up with as the portion of time the heater is on vs off.  This duty cycle which will vary both with ambient temperature and the desired amount of heat and will ultimately determine the impact it has on my range.

I was going to make a short video on the operation and the various systems that control the heater however the ambient temperature this afternoon is too hot for the heater to even turn on.  There will be plenty of chances to do so in the coming months as the temperatures drop.  We have had some chilly mornings so time permitting I will demonstrate the system in action soon.

I still need to create some sort of indicator to make sure I know the heater is “on” and don’t have it on needlessly wasting power if it’s not required.


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