Daniel's EVPorsche 911 conversion - Page 20

JRP3 · 06-08-2009, 06:21 PM

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 · 06-09-2009, 08:42 AM

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 · 06-09-2009, 08:53 AM

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 · 06-09-2009, 09:53 PM

Quote:

Originally Posted by DavidDymaxion

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.

Quote:

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 · 06-10-2009, 07:46 PM

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 · 06-11-2009, 07:20 AM

Quote:

Originally Posted by DavidDymaxion

... 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 · 06-11-2009, 09:40 AM

Quote:

Originally Posted by daniel

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 · 06-11-2009, 09:29 PM

Quote:

Originally Posted by dimitri

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 · 06-11-2009, 10:23 PM

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:

Quote:

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

JRP3 · 06-12-2009, 06:05 AM

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