Daniel's EVPorsche 911 conversion

[daniel]

I can speak a lot on a subject of PS pumps, since I have done both electric and mechanical PS in my EVs. Most people get hung up on saving energy from PS pump, not realizing that amount of energy used by either electric or mechanical PS system when driving straigt line ...

So what you are saying is that the belt-operated pump is actually not placing significant drag on the system when I'm driving straight (which is most of the time). That's interesting, and is consistent with my observation that when I take my foot off the pedal, but leave the car in gear, it seems to coast very smoothly, without noticeably more drag than if the tranny were out of gear.

Thanks for that information! This directly contradicts what the local guys are saying.

 

[daniel]

The cars on eBay are nice looking. Both are older cars. I wanted a newer car so that all the conventional components would have less wear, and also so that I would have stability control and ABS, though in fact I seem to have lost both in the conversion.

I am skeptical of the claimed range, unless those older cars are much lighter than my newer one.

If I had been aware of anything like either one, though, before I bought mine, I'd have flown out there to test-drive. I will be interested to see what they actually sell for.

 

[dimitri]

I bet you'd have much better luck with Jungle Motors. I spoke with Brad over there a couple of times, exchanging ideas for LiFePo4 chargers and BMS, he is very knowledgeable and seems to stand behind his work. He is doing a great job with conversions, and although I am still sceptical of advertised range, I have no doubt in rest of his specs. Although I wish they spent a little more effort in wire managing, spaghetty wires ruin cool electric under the hood image, IMHO.

I am pretty sure those are 160AH cells, same ones I used. However, he has 48 of them for 153V nominal pack voltage. With Warp9 and Raptor controller that you can see in there, the car can easily go for 100+ miles, but not freeway speeds. Freeway range has to be like 80 miles, I guess.

 

[WarpedOne]

So PS losses account for 0.1% - 0.5% of energy used in EV.

I'm sure I've read somewhere classic mechanical PS systems use about 5% of energy. I think it was in a paper article about new wonderful electric PS systems. It goes along not believing all that you read

 

[TEG]

For most conventional front engined cars, the engine sits right on top of the steering rack, and so the PS pump is really close to the power assist on the steering. For a rear engined Porsche it has to pump high pressure fluid all the way up front which I imagine takes more effort.

Re: Electric power steering - AutosTalk Forums

...In general, electrical conversion (alternator/motor/wiring) is significantly more efficient than a hydraulic system of the same size/weight/cost...

dimitri has been here:
Power Steering Options - DIY Electric Car Forums

ELECTRIC POWER STEERING IMPROVES PRODUCT LINEUP | Ford Motor Company Newsroom

DEARBORN, March 31, 2008 – Ford Motor Company has made a commitment to fit 80 to 90 percent of its Ford, Lincoln and Mercury products with electric power steering (EPS) systems by 2012, improving the overall fuel economy, performance and reliability of the company's lineup.

...

The EPS system in the Escape and Mariner is highly sophisticated with features such as active returnability and active damping that help correct for road irregularities and improve overall handling and steering feel. EPS also improves fuel economy, because unlike the common hydraulic-powered systems that continuously draw power from the engine, EPS draws power from an independent electric motor only as needed. According to some estimates, this on-demand capability can equal up to a one-mile per gallon improvement in fuel efficiency. For Escape, EPS and a number of other new features and technologies contribute to an 8 percent increase in fuel economy versus the previous model.

Note, 1 MPG improvement would be 5% on a 20MPG car...

 

[TEG]

By the way, for what its' worth, Toyota uses an ultracapacitor to power the power steering rack in their hybrids. I guess this is one application where short term energy storage with high cycle life and having high voltage in a small package makes more sense than a battery.

 

[TEG]

Another link:

Know your power steering - Team-BHP

 

[dimitri]

My numbers were reflecting idle mode of PS, but when its actually used it would take much more power. For example I saw up to 50 Amps on electric PS pump when in hard turn at low speed or standing still. That would be almost one horsepower, although still not 5%, but closer to it. However, cosidering that PS only kicks in for few moments during typical drive, its not a big deal.

Many modern cars have electric PS, where the motor is actually attached to the steering column, no hydraulics at all. That is very difficult to adopt into another model car. But some cars have EHPS, Electric-Hydraulic PS, where electric motor pumps the fluid. This pump can be put in any car, which is what I did with Toyota MR2 pump in Mazda Miata.

Pure electric PS systems had lots of issues, many GM lemons were reported due to electric PS failures.

 

[dimitri]

Also, MR2's pump has VSS input ( Vehicle Speed Sensor ) which senses speed and turns off the motor completely, not even idle, after certain speed is reached. This would be ideal hookup in EV, although I could not do it in 2001 Miata since it had a non standard VSS signal, not compatible with Toyota.

 

[JRP3]

I was going to bring up the point that Dimitri's measurements of the electric power pump may be much more efficient than mechanical ones, and it seems the articles TEG has posted back up this possibility. It won't transform a vehicle but it might be a worthwhile modification. Luckily my Fiero came with manual steering so I don't have to deal with it.

 

[daniel]

I think someone earlier asked whether my ammeter was between the battery and the controller, or between the controller and the motor.

I do not know for sure, but I presume it's the amperage within the battery, because the amp-hour meter and the ammeter both run both ways: During driving the ammeter reads negative for discharge and the ah meter shows numbers going ever more negative and during charging the ammeter shows positive numbers (24.9 amps until very near the end of the charging cycle) and the ah meter shows the negative values approaching and finally reaching zero, and then going a little bit positive. After a block or two of driving, the ah snaps to zero, and then goes negative again as I drive.

Daniel

 

[dimitri]

Yes, that means your ammeter is on the battery side, that helps in proper energy calculations, since motor side amps are not very relevant in normal conditions.

Also, as I promised to test my EV on a freeway to compare our numbers, I ran a dozen miles of a freeway stretch last night. Cruising at 75mph I was using 32kW of energy, which translates to 426 wh/mile. This was with all windows rolled up and no air conditioning.

Cruising at 65mph with windows rolled up I get about 370wh/mile.

Cruising at 60mph with windows down is about same as 70mph with windows up.

I can see anywhere between 150 and 250 battery amps while cruising at speeds between 50 and 75 mph.

 

[EVnut]

EVNut: The Chrysler TEVan and the Commutavan both had multiple gear ratios.

Ah. For some reason I wasn't counting those. While I've heard of them, I have no clue how many were actually turned out.

Though not a production car, the Buckeye bullet that went 315 mph had a 5 speed tranny -- that settled the debate for me!

Yeah, if your goal is that kind of speed, it would be tough to do with one ratio! I keep getting mired in the practical world.

 

[DavidDymaxion]

Daniel et al, several topics in this post:

Power steering: Power used can be highly variable. On the race track, a power steering pump can get so hot it boils the fluid out! I also learned (for my GM car at least) the PS pump pumps the full volume of fluid continuously -- it is always pumping -- but valves divert it to help assist upon demand. It pumps enough for full power at idle, and 10x as much as needed at max rpm. So these are ways to say the losses might be higher than you'd expect. So what would I do? Put your hand on the pump right after a long drive. If the pump is hot, it is wasting power, and it might pay to go electric. If it is cool, I wouldn't worry about it. Last random thought: I've wondered how much effect highly crowned roads would have -- what if it takes constant pressure to keep the car going straight?

Whr/mi: I would expect your Whr/mi numbers to show a greater difference between the low speed numbers and the high speed numbers. It could be this merely reflects the type of driving cycle you have, or it might indicate something is dragging. Unfortunately, we humans are not very good at detecting dragging parts until it gets really really bad. A fairly bad drag would only be a small fraction of a gentle stop. Here's what I propose: Time how long it takes the car to coast down from 20 mph to 10 mph (or thereabouts, go slow enough so wind resistance isn't a factor). Do it on level ground and a nonwindy day. Do it several times in both directions to cancel slope and wind effects. We can figure out what the rolling resistance drag is pretty easily then.

(V1-V0) / (T1-T0) = ug

Average all the u values.

u = your rolling resistance. 1% or less is excellent, 1% to 2% is pretty typical, well above 2% means there's a good chance something is amiss.

EVNut: I believe more TEVans and Commutavans were built than Teslas so far, but I hope and expect that to reverse soon! I'm a little bummed the Tesla didn't keep it's 2 speed tranny, then it could kick butt on the Salt Flats and faster race tracks, and I believe that would improve its efficiency a little bit.

 

[daniel]

... Put your hand on the pump right after a long drive. If the pump is hot, it is wasting power

[...]

Time how long it takes the car to coast down from 20 mph to 10 mph (or thereabouts, go slow enough so wind resistance isn't a factor). [...]

(V1-V0) / (T1-T0) = ug

Average all the u values.

u = your rolling resistance. 1% or less is excellent, 1% to 2% is pretty typical, well above 2% means there's a good chance something is amiss.

I will do both the above. Except that I'll use my handy-dandy infrared thermometer to check the temperature of the p/s pump.

What units do I use for the ug formula? I'll guess mph and seconds. I think different units would give different results.

Daniel

 

[doug]

What units do I use for the ug formula? I'll guess mph and seconds. I think different units would give different results.

You just want the units to be consistent.

That u is actually a Greek 'mu', like a coefficient of friction, and is dimensionless (no units).

g is the accelleration due to gravity. g=9.81 m/s^2

Go ahead and measure your velocities in mph (miles per hour) but convert them into m/s (meters per second).

e.g.
20 mph = 8.94 m/s
10 mph = 4.47 m/s

 

[EVnut]

anyone who speaks of direct drive has no idea of currents involved, direct drive is possible, but not effective at all, you need gears, especially with air cooled DC motor, which doesn't have much useful RPM band.

Dimitri -

While I have zero experience with conversions, I have plenty of experience with direct drive EVs. Direct drive is not effective at all??? You lost me there. All production EVs of the 90's were direct drive, and did just fine in the range of 0-80 mph. Of course these were all AC motors. Is that were the disconnect is? Or maybe what TEG points out - that there are gear reductions in all of these. We still call them "direct drive" since there is no way to disconnect the motor from the wheels, nor a way to change gear ratios. I must just not understand your meaning of "direct drive."

 

[TEG]

He clarified his statement and said he meant that many DC motors have such a narrow power band that they really needs a gearbox to shift.
He knows there are AC motored vehicles with single speed gearboxes.

----------------------------------------------------------------------------------------------

...although... there are some DC powered vehicles that do OK with no gearbox.

For instance, the Tango:

Drivetrain: Direct 4:1, one motor to each wheel

 

[JRP3]

Yeah, if you have a light enough vehicle with a large enough motor you can do direct drive even with DC. Example
KD's 2006 Factory Five Coupe Kit Car

 

[dimitri]

This only proves my point of DC direct drive not being effective. He has 288V LiPo pack, but only gets 30 miles range. AH size is not listed, but with 900 cells I am guessing about 150-200AH in 10P-90S configuration. Range is sacrificed for torque and speed,both of which SUCK AMPS. You can't have everyting with DC direct drive because of limited RPM range, so something has to be sacrificed.

EVnut, my statement was specific to Daniel's case. I wasn't talking about AC drivetrains, since obviously on a Tesla forum everyone is aware of such possibility :smile:

Most direct drives seem to be ground up builds, or major reworks of a kit car, etc. Daniel's case is a typical street car with swapped motor, so its not effective to lock it in 3rd gear as was suggested by some people. It can be done with a huge controller, but range will be shot to death.