Daniel's EVPorsche 911 conversion - Page 19

JRP3 · 06-08-2009, 06:34 AM

Quote:

Originally Posted by William3

Porsche : 911:eBay Motors (item 190312545943 end time Jun-11-09 14:02:16 PDT)

Porsche : 911:eBay Motors (item 190312548377 end time Jun-11-09 14:15:11 PDT)

Interesting, the red one is using an Azure Dynamics system, which is AC, the black one looks like a Warp9 with maybe a Raptor controller which is of course DC. Can't tell the size of the battery pack though.

daniel · 06-08-2009, 06:46 AM

Quote:

Originally Posted by dimitri

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 · 06-08-2009, 06:50 AM

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 · 06-08-2009, 06:58 AM

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 · 06-08-2009, 02:54 PM

Quote:

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 · 06-08-2009, 03:09 PM

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

Quote:

...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

Quote:

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 · 06-08-2009, 03:12 PM

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 · 06-08-2009, 03:14 PM

Another link:

Know your power steering - Team-BHP

dimitri · 06-08-2009, 03:28 PM

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 · 06-08-2009, 03:31 PM

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.