Electric car conversion: Project ForkenSwift - Page 48 - Fuel Economy, Hypermiling, EcoModding News and Forum

MetroMPG · 11-27-2007, 07:44 PM

Quote:

Originally Posted by 2ton

That's about what you figured at 48 volts. Was that measured with or without the extra batteries?

Yep, pretty close. I figured about 100 lbs lighter.

That's the weight with 8 batteries / 48v.

For 72v, add 256 lbs (four more batteries) + 30 lbs (rack & cabling) for a total of 2363 lbs / 1072 kg.

MetroMPG · 11-27-2007, 07:45 PM

Just learned that the provincial sales tax paid on items bought for an EV conversion is refundable. Cool! That'll save us a few more bucks. (We've just passed $650 CDN net, and I was beginning to worry that the spending was getting out of control.

)

MetroMPG · 11-27-2007, 07:46 PM

Today... skooled by the EV masters was I.

I asked a question on the EVDL about driving technique. I was pretty sure about the best efficiency methods, but not so much on how to make it accelerate faster.

Someone sent me an excellent summary of efficient vs. aggressive dc/serial motor EV technique. This was part of documentation that came with his old Jet Electrica (commercial Ford Escort conversion).

Result of skooling: easily lopped 1/3 off my 0-30 mph time

It's enough of a difference that now I'd consider driving it on some of the grown-up roads that I thought were off-limits.

The trick in a nutshell (pretty obvious when you think of it): mat it, and short shift. DC serial motors make the most torque at low RPM being fed lots of amps, so max out the current limit on the controller, watch the ammeter and upshift as soon as battery current falls off the limit as a result of motor RPM rising.

My previous attempt at 0-30 (before the car was legal) was done in 1st & 2nd. I did it this evening in 1st-4th and the difference was obvious. Whee!!

Quote:

Originally Posted by 2ton

So all you need now is a new gearbox.

1st 10:1 for the first 2 meters...
2nd 3:1
3rd direct
4th 0.5:1

good luck finding it

Very interesting...

MetroMPG · 11-27-2007, 07:48 PM

Got my Killawatt equivalent on the weekend.

Good thing too - the car is way more efficient than I estimated before!

I estimated electricity use based on the nominal 120vac draw listed on the tag on the 24v/5A charger. But charger current tapers down as the batteries charge, so its average current is much less than nominal. Also, the charger switches on/off regularly (thermal protection) when supplying the first (highest current) part of the charge.

I wouldn't have clued in to either of these things without the energy meter.

So...

23.x hours per charge for 24.8 km travelled
5.1 kwh consumed (per the Killawatt) using the 24v/5A charger

@ 6 cents per kwh (standard Ontario energy mix rate - Ivan's house)

0.306 $ per charge
24.8 km/charge
0.012399 $ per km
1.2 cents/km

@ 9.1 cents per kwh (100% renewable energy rate - my house)

0.4641 $ per charge
24.8 km/charge
0.018714 $ per km
1.9 cents/km

Compare to gasoline cost for the Blackfly @ 75 mpg (US) & $1 / L ...

3.14 L/100 km (3.14 = 75 mpg (US))
0.0314 L/km
1 $/L
0.0314 $/km
3.1 cents/km

MetroMPG · 11-27-2007, 07:48 PM

The car's energy efficiency from the above figures...

(5100 wh / 24.8 km) / 1.61 km/mi = 127.7 wh/mile (EDIT: there's a big fat error in these calculations. See further down the thread to read where I realized it.)

And that's based on charging. And that's insanely efficient, compared to other EV figures I've seen. (Of course it represents my driving & avg speed of probably 20 km/h)

MetroMPG · 11-27-2007, 07:49 PM

Quote:

Originally Posted by SVOboy

big time

For comparison: Tesla recenty did the EPA test cycles for the roadster. In city driving, it's rated for 300 wh/mile (also based on energy usage at the charger).

http://www.teslamotors.com/blog4/

VP1 undergoes range testing on the dynamometer

MetroMPG · 11-27-2007, 07:51 PM

Quote:

Originally Posted by skewbe

127 wh/mile doesn't seem too awful by comparison to 300. It would be like a 20mpg car compared to a 45mpg car, sort of.

Very cool all the same, the forken that is. Do you think the tesla can be hyperwatted? 10kwh/day seems a bit much. Is it as simple as crawling to minimize battery losses?

The Tesla is undoubtedly far more efficient battery-to-wheels than the FS is, and it would spank the FS embarassingly in a hyperwatting competition.

I've read that their charger is a bit of an energy hog because the charging process includes actively cooling the pack while force feeding it the juice. So in a charger-to-wheels comparo, that's one reason (of several) why the FS looks relatively good.

Evidence (claim) of on-road Tesla spankness:

Quote:

Quote:
Tesla also reported the battery-to-wheel efficiency as 110 Wh/km (177 wh/mi) on an unspecified driving cycle (either a constant 60 mph (96 km/h) or SAE J1634 test[21]) - wikipedia

MetroMPG · 11-27-2007, 07:51 PM

Whoops - just uncovered a big mistake in my calcs. Divided where I should have multiplied doing the km to miles thing.

The ForkenSwift just crashed into Mars.

FS is 331 wh/mi, not 127.

Drat, Tesla wins, even with me driving 20 km/h.

No more fiddling with spreasheets past my bed time.

Quote:

Originally Posted by SVOboy

Haha, wow! That's a pretty big oops right there...

At least your still on par with the professionals...

MetroMPG · 11-27-2007, 07:53 PM

Quote:

Originally Posted by omg

If ya had li-ions you'd be at 231Wh/mile and given that the Tesla's charger is such a hog, they're likely more than 127Wh/mile from the plug. Just sayin...

Here's some more from GCC

Quote:

Henrik,

Click "Where the Rubber Meets the Road" above and scroll down to the section on Range Testing. They show recharge energy of 31 kWh/100 miles for combined cycle. That's at the wall plug, not the battery. As you note, the car only needs a little over 200 Wh/mile from the battery. This means 1/3rd of the wall plug energy is lost in the charging process. Tesla's well-to-wheel white papers claim 90 or 95% charging efficiency instead of the 65-70% implied by this data. That's a huge gap.

Ok I get it. That is an interesting observation. Wonder what went wrong. Lithium batteries should have very high charging efficiency near 100% according to http://www.batteryuniversity.com/partone-12.htm. So the problem must be the charging transformer. As far as I remember they often lose a lot of energy possibly 30% but it is possible to buy some that loose very little energy. Maybe they have chosen a model that is cheaper and perhaps lighter but that waste more energy in the conversion. Most people will never notice such a change anyway but you do. Plus electricity is still very cheap compared to gasoline so the economics is still ok and the people that can afford a Tesla will not care about the economics of driving anyway.

Remember that the EPA tests that tesla ran now include running the air conditioner. The california sun beating down through the windows, and on a dark green roof will require alot of air conditioner power to keep temperate. That could explaine alot of the difference between the 216 WH/mile that they got when actually commuting (probably with the top down), and the 310 WH/mile they got while running the EPA designed tests (top up, air on).

Coalburner, the problem with your theory is they show 245 mile range on the combined test.Even if they used all 53 kWh in the battery pack that only comes out to 216 Wh/mile. The diff between 310 and 216 is apparently charging efficiency. It's a really horrible result, hopefully caused by a really inefficient non-production charger. If not Tesla needs to completely re-do their well-to-wheels white papers.

Update, Tesla deleted my question but in response to another message said the difference between 216 and 310 Wh/mile was due to charging inefficiency, including the need to run a cooling system to keep the batteries cool during charging!

Somehow I doubt they'll update their well-to-wheels paper or stop making their ridiculous "penny per mile" claims. Tesla is doing good work but there's no shortage of snake oil, either.

Good diggin', omg. Thanks for posting that.

On at least the speed/acceleration front, there's little debate which car is superior...

I did an acceleration run (on fresh, happy batteries)...

0-50 km/h (31 mph) took 36 seconds

ForkenSlow!

MetroMPG · 11-27-2007, 07:53 PM

omg provides some good info...

Quote:

Originally Posted by omg

If ya had li-ions you'd be at 231Wh/mile and given that the Tesla's charger is such a hog, they're likely more than 127Wh/mile from the plug. Just sayin...

Here's some more from GCC

Quote:

Henrik,

Click "Where the Rubber Meets the Road" above and scroll down to the section on Range Testing. They show recharge energy of 31 kWh/100 miles for combined cycle. That's at the wall plug, not the battery. As you note, the car only needs a little over 200 Wh/mile from the battery. This means 1/3rd of the wall plug energy is lost in the charging process. Tesla's well-to-wheel white papers claim 90 or 95% charging efficiency instead of the 65-70% implied by this data. That's a huge gap.

Ok I get it. That is an interesting observation. Wonder what went wrong. Lithium batteries should have very high charging efficiency near 100% according to http://www.batteryuniversity.com/partone-12.htm. So the problem must be the charging transformer. As far as I remember they often lose a lot of energy possibly 30% but it is possible to buy some that loose very little energy. Maybe they have chosen a model that is cheaper and perhaps lighter but that waste more energy in the conversion. Most people will never notice such a change anyway but you do. Plus electricity is still very cheap compared to gasoline so the economics is still ok and the people that can afford a Tesla will not care about the economics of driving anyway.

Remember that the EPA tests that tesla ran now include running the air conditioner. The california sun beating down through the windows, and on a dark green roof will require alot of air conditioner power to keep temperate. That could explaine alot of the difference between the 216 WH/mile that they got when actually commuting (probably with the top down), and the 310 WH/mile they got while running the EPA designed tests (top up, air on).

Coalburner, the problem with your theory is they show 245 mile range on the combined test.Even if they used all 53 kWh in the battery pack that only comes out to 216 Wh/mile. The diff between 310 and 216 is apparently charging efficiency. It's a really horrible result, hopefully caused by a really inefficient non-production charger. If not Tesla needs to completely re-do their well-to-wheels white papers.

Update, Tesla deleted my question but in response to another message said the difference between 216 and 310 Wh/mile was due to charging inefficiency, including the need to run a cooling system to keep the batteries cool during charging!

Somehow I doubt they'll update their well-to-wheels paper or stop making their ridiculous "penny per mile" claims. Tesla is doing good work but there's no shortage of snake oil, either.

Good diggin', omg. Thanks for posting that.

On at least the speed/acceleration front, there's little debate which car is superior...

I did an acceleration run (on fresh, happy batteries)...

0-50 km/h (31 mph) took 36 seconds

ForkenSlow!