Electric Porsche – Parts revision

With any project parts selection is a difficult process, balancing budget/performance/availability isn’t always easy. After many more calculations it’s very clear that the battery pack will be the limiting factor on the actual power output of my Porsche conversion. So unless I plan to upgrade the battery pack, using the Kostov 11″ motor and Soliton1 are simply overkill which wastes money that could otherwise be put towards the limiting factor which is batteries (I will state that the Soliton1 isn’t a waste of money, it looks like an amazing piece and if the funds are there when it’s time to buy a controller I will choose it over the Warp Drive, however if the funds aren’t there the latter will prevail).

I’ve decided on the Warp 9″ motor, which is common to many many car and truck conversions, it’s reasonably priced, good quality and definitiely proven.

 

The Warp9 should also provide good performance, with the new controller I have chosen I should still be able to get between 237 and 339ftlbs of torque at maximum motor current which will be between 1000A and 1400A this is still quite a bit more than the stock 2.5L motor. Using the 1400A version of the controller the 9″ motor would put out more torque than any of the stock engines of any year the 944 was produced for both the Turbo and NA.

This new controller is also from the Warp family in the form of a Warp Drive 160V 1000A/1200A/1400A beast. The hardware is all the same, and software upgrades unlock the higher current levels ($$$). Higher voltages are also unlockable with software updates with the appropriate exchange of $$$ of course. The nice part is the controller is about $1000 less than the Soliton1 in basic form, with optional but slightly expensive upgrades to allow more power output than even the Soliton1 is capable of. One of the nice parts of this is the controller is designed for it’s maximum power level and scaled back in software to the basic versions, so the controller will not be pushed to it’s limits and should last for many many years.

The controller uses a CAN bus system for expansion and if a few companies get on board there could be a nice selection of extras available in coming years. Since the maximum voltage for the controller is 160V in the form I will be using the battery voltage must be scaled back, I will be using 48 Thundersky cells instead of 90 for the 288V pack, however I will be using larger cells to get a slightly larger pack size than the original design. The new nominal battery voltage will most likely be 153.6V at 200Ah, which is about 15% larger than the previously planned pack. I could also drop down to 160Ah cells which would make a pack just slightly smaller than the previous design, at the cost of continuous current which reduces maximum power.

Peak power (only limited in duration by the amount of heat the motor can dissipate) is 86,400 Watts, the controller and batteries can handle this power on a continuous basis, however the pack would be dead pretty quickly. If I am able to find a source for the CALB 180Ah 4C cells peak power would increase to 103,680 watts. Peak torque is based on the amperage output of the controller, at 1000A being 237ftlbs, 1200A around 288ftlbs and 1400A around 339ftlbs. The RPM range for this torque level will be zero to x rpm where x is the point where current starts to get traded for voltage by the controller based on the current limit of the battery pack. It should be around 2000-2500rpm. The higher current CALB cells would allow maximum torque up to a higher RPM, but either pack will allow full torque at low RPM. To get maximum range the battery current will have to be kept to a reasonable level, so just the same as a gas car, the harder you press the gas the lower your fuel economy gets. With all the upgrades the controller is capable of over 1/2 a megawatt of power or the equivalent of 675 horsepower. However that would require a bigger motor and better batteries than I ever plan on putting in the Porsche.

Right now the car has about 2/3 of a tank of gas, when it’s empty the engine comes out. The gas parts start to go up for sale and the electric motor will get ordered, so I still have a little time to change my mind again on motors.

Electric Porsche – the idea

For a few years I’ve toyed with the idea of converting a polluting and inefficient gasoline car to electric. With the cost of batteries and other components building an electric car for the sole purpose of saving money on gas just doesn’t work. However there are many other reasons to make the switch. It’s becoming very obvious that Global Warming is real, it’s affecting us today, it’s no longer a prediction or a catch phrase used by environmentalist. The oil disaster in the gulf is another example of what our continued dependence on fossil fuels can do, and will continue to do to the environment. I’m happy to see that there are a few commercial offerings in the car market today, with Tesla’s Roadster, and soon to be released sedan, along with the Nissan Leaf, Chevy Volt, and many others that have at least gotten to the concept car stage. The future is looking brighter as far as alternative energy is concerned.

Another motivation in converting the Porsche from gas to electric is simply the process itself, I enjoy designing, building and solving problems. Also, I like to be different, living in Calgary AB which is arguably the oil capital of Canada, there are barely a handful of highway capable electric cars that I know of in the entire province. I would like to take one step towards changing that.

I decided to convert a Porsche 944 for two reasons, 1) it’s small, relatively light, drives well, with good parts availability. 2) it’s a Porsche, it draws attention regardless of what’s under the hood, however as an electric car, I hope it generates more interest and gets rid of a few myths about what an electric car has to be, and show what an electric car can be.

Once converted the operational and maintenance costs are very low, electricity should cost about 2 cents per km, vs 13-15 cents per km at current gas prices (92.9/l) in my G35. It’s also pretty fair to say gas prices are only going to go up in coming years. There is also less maintenance for electric cars, of course they need the basics, tires/wipers/washer fluid, however there are no more oil changes, some cars may not use transmissions (my conversion will retain the 5 speed manual). There is no massive cooling system, since electric motors are greater than 80% efficient vs ~15% for gas engines. There is one drawback though, no free (waste) heat to warm the cabin on those chilly days, an efficient and dedicated heating system needs to be installed, however you no longer have to wait for the engine to warm up before you get that heat. The electric motor should go for 50,000 to 100,000km before requiring its major service, which is new brushes (~$100-$200). Cars like the Tesla and Nissan Leaf are using brushless AC motors that won’t even need this service, making bearings virtually the only part that can wear out. Brakes will also need less service on the Tesla and Nissan, however my conversion without “Regen” will still require regular brake system maintenance. I may look at a method of converting some of that energy to heat electrically instead of by friction.

The Porsche 944 is known for its classic styling, great handling, and expensive maintenance. Well at least most of it is good, I will be removing the main source of that expensive maintenance as the 2.5L 4 cylinder gas engine. No more timing belts, counterbalance shaft belts, oil seals, spark plugs, motor mounts, clutches to replace (and that’s only if your engine is running perfectly). The cooling system, exhaust system, and fuel system will also go, I will have to do more research but it looks like the car’s computer can also go. All of these parts will be sold off to help pay for the electric replacement parts that will be going in.

Replacing the engine will be a Kostov Motors 11″ Series wound DC motor.

Rated at ~40kw continuous power at 192v & 250A and capable of much more than that for short periods of time (ie. at 1000A) it should make the Porsche just as much fun to drive in electric form as it was as a gas car. The peak HP of the electric motor will be similar to the gas engine, however the torque output will be in the range of 2-3x that of the gas engine. Fortunately the car I bought has the transmission from the 944 Turbo which is apparently much stronger and can handle more torque than the regular version.

The motor will be controlled by a high power DC motor controller, capable of 1000Amps continuous at 300V DC (300kw) unfortunately both the motor and batteries will not be able to support this, and I will be limited to between 100kw and 150kw depending on the battery pack.

The battery pack will consist of a 288v series string of ~90aH LiFePo4 cells. I will be looking at a total pack size of 20kw – 30kw which should give a conservative estimated range of 100 – 150km per charge (in a perfect world the calculations predict 250km, however that is for non stop cruising at about 90km/h on flat ground)

The batteries can be charged from either a 110v 15A ”normal” plug, or much faster from a 220v 30A circuit.

There will be some extra work required in adapting the power steering, air conditioning and heat to work with the electric conversion. Since the motor doesn’t “idle” when the vehicle is stopped there would no longer be power to the AC or power steering, I will have to look into different dedicated electric systems to power these items. I had considered removing the AC system all together, however the main goal of this conversion is simply change the power source of the car, not to change any functions or convenience features of the car.

The lucky car is a dark grey 1986 Porsche 944 with the 2.5L NA engine, with a “wet” curb weight of around 2800lbs I am hoping for a final conversion weight around 3000lbs or less. While maintaining the perfect 50/50 f/r weight distribution as designed by Porsche.

The car needs some minor body work, however for a 25 year old car with original paint it’s in pretty good shape. The interior is pretty much mint with the exception of some small cracks on the dash. The Porsche will be driven for a few months to get a good feel for the car, and find out if anything else needs replacing, as well as get an idea of fuel economy so I can get a better estimate of what to expect when it’s electric.

The engine will come out in the next few months stay tuned.