Daniel's EVPorsche 911 conversion

[daniel]

Today, using about the last of my "safe" battery charge (until the cable comes, promised for Monday) I drove very gently to the library, the store, and home, and then to the drugstore and home. If my calculations are correct I got 373 wh per mile.

I'd say that's acceptable performance for a car that was not engineered: I am sure Paul uses off-the-shelf components. And its roughly what my much lighter Zap Xebra gets.

The problem is that I was supposed to have a 225 v system and 125 miles of range. I'm thinking he just could not fit enough batteries in the car.

Note: I think I misspoke before: I may have said he promised a 256 volt system. The contract says 225 v. I apologize for my error.

Re-gen can make a big difference in hilly terrain, or when there are lots of stops and starts. On the freeway (which is where I am concerned about range) it does no good at all.

Another problem with re-gen is getting it to work the way I would want it: I think re-gen on the go-pedal is a very bad system. I want my car to coast, not brake, when I take my foot off the go pedal. I want a car to use re-gen only when I step on the brake pedal, instead of using the brake pads. But that requires a very sophisticated system with computer control and assurance that the brake pads will be used in a panic stop or if the re-gen or the computer fails. The Prius has such sophistication (though it also uses re-gen when you lift off the go-pedal).

Given my flat terrain, my dislike of re-gen on the go pedal, and my need for range only on the freeway trip to Coeur d'Alene, I think Paul was right in recommending against re-gen.

Today I figured out how to use the radio, which sounds VERY nice, and the moon roof, which is cool.

 

[mpt]

If I remember rightly; the 911 has rear tires like road-rollers on account of it having its engine where the tail-lights should be

I wonder what the weight balance is now with it having batteries (heavy) and motor (lightish - the 911 motor is light for an ICE).

Would it make sense to down-size the rear tires to reduce rolling resistance?

I also wonder how the ride height is; the standard 911 rear suspension expects a certain weight to position the rear tires; the slightest change can quickly tear up the insides of the tread; I've seen 5mm rubber on the outside and cloth on the inside before on a friends 911 S4.

Just musing; Elon Musk said that converting an existng car was tricky because everything had to be changed. What else was changed above the ICE swap?

MPT

 

[daniel]

If I remember rightly; the 911 has rear tires like road-rollers on account of it having its engine where the tail-lights should be

I wonder what the weight balance is now with it having batteries (heavy) and motor (lightish - the 911 motor is light for an ICE).

Would it make sense to down-size the rear tires to reduce rolling resistance?

I also wonder how the ride height is; the standard 911 rear suspension expects a certain weight to position the rear tires; the slightest change can quickly tear up the insides of the tread; I've seen 5mm rubber on the outside and cloth on the inside before on a friends 911 S4.

Just musing; Elon Musk said that converting an existng car was tricky because everything had to be changed. What else was changed above the ICE swap?

MPT

I cannot answer any of your questions. Paul has been converting Porsches (mostly --maybe exclusively-- using lead batteries) for years, so he probably understands the weight issues, and has probably adjusted the suspension if that's necessary. But I'd imagine he has not changed much other than swapping the engine and associated components for the motor and batteries and associated components. His web site may have technical information that I would not understand. It's CoolGreenCar dot net.

I am not a car enthusiast or mechanic. I'm just a guy who hates everything about gasoline, from its stink to the economic impact of importing our energy. I bought a Prius in 2004. I liked the brief moments of electric operation, and two years ago bought a Zap Xebra after a visit to Tesla Motors left me disappointed with the comfort of the Roadster, and unwilling to wait the year-plus they then estimated. The Porsche seemed the solution to the Xebra's inadequate range, but as much as I enjoy driving it, its range falls far short of what was promised.

 

[TEG]

You are a doubly perfect customer for them... You aren't too concerned with acceleration performance, and you don't want regen. Sounds like you may end up having a conversation with them about the range though.

 

[JRP3]

For all intents and purposes regen is not possible with series DC motors, so it was never an option in this case. A Warp 11 motor retails around $3k, a Zilla 1000 amp high voltage controller, what you would have gotten with the promised 225 volt system, used to sell around $2500. A comparable AC system with regen would run you more than $8K. Regen does not give back all that much anyway unless there is a lot of stop and go and hills involved.
The higher voltage system you were supposed to get would have been more efficient due to lower amp draw and therefor less waste energy as heat. It also would have given much better acceleration. Essentially it's like paying for a V6 and getting a 4cylinder, but with the mileage of a V8. OK, not quite that bad but that's the basic idea. I don't know if I buy the lack of room for more batteries, he could have used more smaller cells to get the voltage up. Either way he should have been aware of what he was doing and credited you for the lower specs or told you ahead of time about the change. My guess is he had to go with the lower voltage because he could no longer get the Zilla HV controller and the replacement couldn't go above 144.
If you can get under 400 wh/mi with normal driving and closer to 300 by taking it easy you're probably not doing too badly with that vehicle. I'm not positive but I would think the efficiency range for that motor would be between 2500-3500 rpms. Lower rpms will draw more amps, higher rpms you loose torque and efficiency due to increased back EMF.

If it is assumed that a motor is 100% efficient with no friction or windage losses, the speed of the armature will increase until the back electromotive force is equal to the applied electromotive force, i.e. there will be no net electromotive force, no current flow and hence, no net force. The armature will spin at a constant rate, of its own accord.

Counter-electromotive force - Wikipedia, the free encyclopedia

 

[daniel]

... Sounds like you may end up having a conversation with them about the range though.

Yep. Definitely.

On the positive side, the car handles beautifully. I can take corners much faster than in the Xebra or even the Prius. The Prius does not handle all that well, though it does what it was designed to do admirably. The Xebra handles great considering that it has only three wheels. :biggrin: The Porsche is a pleasure to drive.

Life is full of disappointments, and in the grand scheme of things, my problems fade into utter insignificance. There are people who do not have enough food; people who are losing their homes; people sleeping under bridges; people who cannot afford to see a doctor; people being blown to bits or disfigured in wars. I'm complaining because my too-expensive car does not have the range that was promised to me. I need to get some perspective!

I calculate that I have about 7 safe miles left before I hit 20% SoC, so tomorrow the car will stay in the garage. If the cable arrives as promised, the car will be charged up Tuesday morning, and I'll take it on the freeway until it's down about 30% so I return home with 40% remaining. Wednesday I'll do the same on rural surface roads (steady slow speed, not much stopping) and on Thursday I'll do the same on city streets. I'll post my numbers. Once I know what the car really does, I'll talk to Paul and see what he says. Also, there's a guy 30 miles from here who builds EVs. I'm not sure I'd want him to work on my car, but I'll see what he has to say. He'd probably enjoy seeing it anyway.

Perspective. I have too much money. I've foolishly spent some of it on a car that does not do what it was promised to do. I still have too much money. And a car that does half what I wanted, anyway.

Daniel

 

[JRP3]

Perspective. I have too much money. I've foolishly spent some of it on a car that does not do what it was promised to do. I still have too much money. And a car that does half what I wanted, anyway.

Daniel

But you're also learning much more than you ever wanted to know about EV's , and that's priceless :biggrin:
I don't think you got terribly ripped off or anything, we'll have to see what kind of range and performance you actually end up with. I'm sure it's a great vehicle, it's just too bad that the builder seems to have over promised and under delivered. If he had said "I can't get the same controller so the performance will be slower and the range will be less, and I'll knock $5K off the price", or something like that, it wouldn't be as bad. If I were the builder I'd much rather promise less and deliver more, guaranteeing happy customers, but it's probably harder to make money that way.

 

[TEG]

JRP3s last two posts covered a bunch of stuff I was thinking about, but now I don't have to say. Thanks, JRP3.

 

[daniel]

If he had told me that due to whatever he would only be able to give me 60 freeway miles, for a "safe" freeway range of 50 miles, I'd have canceled the project and asked for my money back, and either looked for another conversion shop that could give me 100 miles, or I'd have sold the car back to the used car dealer. I might have considered paying for more batteries to get the range I wanted, but I don't see how any more batteries could be made to fit. Maybe by taking out the back seat.

Remember that my Zap Xebra goes 40 miles, and I'm willing to take it 35. The high cost of this car is justified of I can drive it 75 miles with, say, 40% remaining for pack deterioration in future years. It is not justified if I can only go 15 miles farther than my Xebra goes safely.

But as I said before: PERSPECTIVE! I have a beautiful car that handles wonderfully. I'd never have bought it if I'd known it would only go 60 miles to empty on the freeway. But life offers worse things than this. Maybe the bottom line is that the Roadster and the eBox are the only EVs there are that can go 100 miles or more on the freeway, and I was asking the impossible. Maybe I need to get my deposit in on a Tesla Model S. Sigh!

 

[TEG]

You probably do want to charge it and drive it some more before concluding what it can really do range wise. Range gauges in EVs can frequently be inaccurate, and you probably can't make an accurate assessment based on extrapolations from going through one cycle of a partial charge.

 

[JRP3]

I agree with TEG, the jury is still out on your actual range and it may end up being better than it appears right now.

 

[daniel]

I don't have a range meter as such. I have an e-meter which shows my choice (only one at a time) of the following: Amperage draw; voltage (but it seems to be the output of the DC/DC converter at around 13 v, not the pack voltage); total amp-hours used since last recharge/reset; percentage of charge used, based on the total ah you've told it, and its measured ah used. I've been told my pack is 200 ah.

I'm going to fiddle with it some more, but I'm not happy that I don't seem to get pack voltage. However, that may be on another gauge that I have not noticed yet. The Porsche is very cluttered with instrumentation. If I could see pack voltage I'd be able to tell when it's actually getting low. LiFePO4 is very non-linear, but you still get an idea, if you understand the non-linearity.

I do consider all my measurements so far to be preliminary. But the fact that they've been fairly consistent is not encouraging.

 

[daniel]

First freeway test:

It is extremely windy today. I had the wind at my back going out, and the wind against me returning. I drove 2 miles to the freeway, then 13.4 miles on the freeway at as close to 60 mph as I could keep it. The cruise control does not function now that the ICE is gone. Then I turned around and came back. I stopped at the Porsche dealer to show off my car, so I probably drove 1 1/2 miles off the freeway, more or less, and came back to it a mile closer to home, so for a mile of the against-wind I was on surface roads rather than freeway.

Altogether I drove 30.8 miles, roughly 25 being freeway, and of that, probably 13 was with the wind and 12 was against the wind. Of course I also had the wind against me on the surface road, but it probably has less of an effect at the lower speed.

I used 88 ah. Going by the specs they've given me: my pack is 28 kWh and is 200 ah, I used 44% of my charge, or 400 wh/Mi. This is not very good. It translates to a total pack range of 70 miles, or 56 miles to 80% DoD which I've been told is safe for LiFePO4 batteries.

In coming days I will repeat the test at 55 mph and at 70 mph (the speed limit here) and on the surface roads. I'll also assess the acceleration at freeway speed.

Daniel

 

[JRP3]

Were you promised 125 miles at freeway speeds? Steady cruising at 30-40 mph or so might keep your wh/mi low enough to get closer to that after everything is broken in and you learn to drive most efficiently. The batteries will take maybe 10-20 full cycles to develop their full capacity and most of the newer LiFePo4 cells come in above their rated capacity, so your 200 ah cells could end up being closer to 210 ah cells. Often EV range is rated at rather ideal conditions, so if it wasn't spelled out specifically the builder may have some wiggle room.

 

[daniel]

I was very clear that I wanted 125 miles at freeway speed. However, the contract does not say freeway speed, so if it went to court he'd have a bit of room. However: ...

UPDATE:

My pack was all topped off at 7:00 p.m., so I took the car out for another drive, this time on rural surface roads. Not really rural, but out-of-town roads. There are stops, but not frequently, so there's a lot of steady-speed driving. This time I held my speed between 35 and 40 mph, and I got 343 wh/Mi. This translates to a pack distance of 81 miles, or a "safe" distance (down to 20% SoC) of 65 miles.

If he says he's not obligated by the "freeway" speed, he still has only provided me with 65% of the promised range. As for driving efficiently, I've been driving my Zap Xebra for two years. I know about efficient driving. I may not be the Willy Mays of efficient driving, but I do understand it, and can drive gently when I choose.

He did say that the motor would improve as it loosens up. He did not say by how much. 10%? 20%?

When I state my range, I am assuming 28 kWh, 100 ah, for the pack. I don't think I have any way of measuring that without driving it to empty, which seems like a very bad idea.

Unfortunately he did not give me a volt meter on the pack!!! The e-meter has a voltage position, but it reads around 13 volts, and apparently is reading the output of the DC/DC down-converter.

Daniel

 

[JRP3]

By efficient driving I mean for that particular motor and vehicle, using your amp meter to keep amp draw to a minimum, which you may already be doing. You also need to get your volt meter to read pack voltage. See if you can find any EV types in your area to take a look at it for you, it shouldn't be that hard to change. Have you spoken to the builder about it?

 

[efusco]

I was very clear that I wanted 125 miles at freeway speed. However, the contract does not say freeway speed, so if it went to court he'd have a bit of room. However: ...

UPDATE:

My pack was all topped off at 7:00 p.m., so I took the car out for another drive, this time on rural surface roads. Not really rural, but out-of-town roads. There are stops, but not frequently, so there's a lot of steady-speed driving. This time I held my speed between 35 and 40 mph, and I got 343 wh/Mi. This translates to a pack distance of 81 miles, or a "safe" distance (down to 20% SoC) of 65 miles.

If he says he's not obligated by the "freeway" speed, he still has only provided me with 65% of the promised range. As for driving efficiently, I've been driving my Zap Xebra for two years. I know about efficient driving. I may not be the Willy Mays of efficient driving, but I do understand it, and can drive gently when I choose.

He did say that the motor would improve as it loosens up. He did not say by how much. 10%? 20%?

When I state my range, I am assuming 28 kWh, 100 ah, for the pack. I don't think I have any way of measuring that without driving it to empty, which seems like a very bad idea.

Unfortunately he did not give me a volt meter on the pack!!! The e-meter has a voltage position, but it reads around 13 volts, and apparently is reading the output of the DC/DC down-converter.

Daniel

Daniel,
I think 65, or even 80 miles range with routine driving is wholly inadadequate considering your intended usage, contract, and expectations. Not necessarily my place to tell you what to do, but I would contact the installer and force him to accept the return.

I know that's a painful choice after the long wait and your desire for a hwy capable EV, but I just don't think you can let this guy sell you a vehicle with 1/2 the range you expected.

Other options include a large refund (1/2 battery cost), or a rebuild to your desired specs with a guaranteed time to return of the vehicle to you (say, by the end of June).

 

[daniel]

By efficient driving I mean for that particular motor and vehicle, using your amp meter to keep amp draw to a minimum, which you may already be doing. You also need to get your volt meter to read pack voltage. See if you can find any EV types in your area to take a look at it for you, it shouldn't be that hard to change. Have you spoken to the builder about it?

Yes, when driving for efficiency, I watch the ammeter during acceleration. Ideally, I'd like to keep it under 100 amps, though I always put safety and courtesy to other drivers ahead of efficiency. So, e.g. on a main artery I will not accelerate slower than the average flow of traffic. Similarly when approaching a stop. I'll coast as much as it's safe and courteous to, minimizing use of the brakes. Obviously, in steady-speed driving there's nothing you can do but try to hold a steady foot on the pedal.

In my testing phase, I am doing some steady-speed driving at different speeds and different gears, to find the most efficient. Because there is little absolutely level terrain, the ammeter jumps around a lot, so I'll drive a course at different speeds and compare the total ah used.

I am waiting until I've done tests at different speeds before I phone the builder again. I want to be able to give him as much information as I can.

 

[daniel]

I spoke with Paul. My controller is a Curtis 144-volt 1231c. My battery pack consists of 96 cells, in parallel pairs of two, for 144 volts total. The discrepancy between the contract voltage and the actual voltage arose because the higher-voltage controller he was going to use (256 v?) turned out to be unreliable. He had two blow up out of a shipment of five, and he decided the Curtis, though less powerful, was the better choice for reliability. He would not have used more cells, but he would have wired them differently had he used the higher-voltage controller.

He still says the car will get more range as the motor breaks in, and he says the batteries will break in also, though I am skeptical of that last statement.

After this conversation, I believe he was acting in good faith, but he overestimated the range I'd get. I suspect that he has less experience with LiFePO4 than I had thought, and this could be part of the problem. The car does not do what I wanted it to, but it will do what I need it to. I would not have paid what I did had I known the range I'd actually get, but I will make the most of what I have and enjoy the much greater speed and 50% greater range compared to my little Zap Xebra. The little three-legged clown car is really a fine vehicle, but the Porsche can do more.

I had asked for 125 miles of range so that I'd never have to worry about battery capacity or opportunity charging, but now I'll try to find out if the community center where my church meets in Coeur d'Alene would permit the installation of a charging spot.

Daniel

 

[vfx]

spoke to Paul...

As you know your miles per charge will also drop in the winter months up there...