P85D vs. P85 Efficiency Testing

[Johan]

You have a FLIR camera? In that case you are making this way more complicated than it needs to be. Rent an hour of AWD dyno time, run the cars in cruise control at the same speed for x minutes. Use the FLIR camera to check the temperature of all electronics and moving parts. You can roughly integrate temperature over volume to get a comparison of wasted energy.

100Wh/mi WILL show up somewhere, it's a massive amount of heat. If it's in the tires, then the tires will be hot, etc.

edit - you will know EXACTLY where the extra energy is going, whether it be in the inverter(s), battery, motors, tires, bearings, transmission, etc. At 65mph on a dyno that's 6.5kW of heat being dissipated. Hell you could probably do it by feel alone.

You're mirroring my thougts exactly, here's what I posted in Elon Musk tweets software upgrade will increase P85D range - Page 10

So anyone care to guess where those extra 50-100 Wh/mile (compared to a RWD Model S) are going (3,25 to 6,5 kWh per hour of going 65 mph)??? We know they're not going towards propelling the car. Also, we know the added weight creates only slightly increased friction, nothing near 50-100 Wh/mile.

Well... Energy "wasted" i.e. not used to propel the car, must come out as heat somewhere. If a FLIR showed the rear motor as being substantially hotter as compared to the rear motor in a P85 (they should be very similar in set up) after an identical drive then it might suggest that in fact the front and rear motors are counteracting somehow?

Would be very interesting to see FLIRs after a dyno run.

 

[randompersonx]

Don't underestimate the ability of the cooling system to "move" this heat. In florida, after charging for a few hours at 10kw, the only heat signature I see is from the front wheels where the cooling system vents out. The rear seats are cool. (test done at 80F ambient)

 

[Bighorn]

I saw this posted somewhere earlier, but I had the same thought:

In addition to the comparison testing, it would be interesting for someone with a P85D to do a test to try to determine, in reasonably "average" conditions (no huge headwind, very cold temps, etc.) how much one has to hyper-mile the P85D to get it to show a) the 380 Wh/mi the EPA range implies; b) the 300 Wh/mi that an S85/P85 needs to do to get its EPA-rated 265 miles.

The 380 EPA figure was identical on both the S85 and P85D and reflects total energy used from the grid, not battery alone--at least that's my understanding.

 

[wk057]

The 380 EPA figure was identical on both the S85 and P85D and reflects total energy used from the grid, not battery alone--at least that's my understanding.

Where are you guys getting 380 Wh/mi? 265/242*300 = ~328.5 Wh/mi for the P85D at EPA numbers...

 

[Bighorn]

Where are you guys getting 380 Wh/mi? 265/242*300 = ~328.5 Wh/mi for the P85D at EPA numbers...

Right off the EPA sticker--it's kind of meaningless.

 

[wk057]

Well, looks like the outside temp is lower than predicted today. (Low 40s, upper 30s). I don't think this should have a huge impact on this side by side test anyway since we're using jackets and hats instead of cabin heat.

Since I may not have a chance to make another attempt in the near future I'm going to proceed shortly.

 

[Johan]

Could you do two tests, one with new tires on the P85D and one where you switch to the ones you have on the P85?

 

[kennybobby]

How much is the weight difference--how much does each vehicle weigh?

What are good values for aero coeff Cd and Area?

Has anyone done some coastdown testing--good way to determine Crr factor.

Run these in a calculation to compare predicted with his measured power.

 

[Johan]

How much is the weight difference--how much does each vehicle weigh?

What are good values for aero coeff Cd and Area?

Has anyone done some coastdown testing--good way to determine Crr factor.

Run these in a calculation to compare predicted with his measured power.

Cd and Cdi is identical, no? Weight effect should be minimal, like an extra passenger or less (certainly not 100 Wh/mile).

 

[wk057]

Hmm... a good side by side coast in neutral might be a nice additional to this test, down a hill on the interstate. I'll try to work that in.

 

[andrewket]

When the P85+ came out, the staggered 21" set up was supposed to provide improved efficiency, (3%?IIRC) vs the P85.

Does the P85D have an Ideal mileage setting? Seems like it shouldn't since it was a throwback to the 2-cycle EPA testing. (Edit--on further review, it's likely based on 55 MPH testing; the 2-cycle test yielded 320 miles)

I've been curious what the Wh/rated mile rate constant is, which you'll have good documentation of if you're videoing the Trip Meter and rated mileage. Should be 275+/-5 for the RWD and 310+/-5 for the P85D.

I would abbreviate any stops for changing drivers, etc so that any unrecorded energy usage is minimized.

I don't ever recall tesla or anyone else claiming the staggered 21" on the P85+ was more efficient then the standard 21" of the P85. If anything, it would be less.

 

[Cottonwood]

Right off the EPA sticker--it's kind of meaningless.

The 380 Wh/mi on the EPA sticker is a "from the wall" number and not a "from the battery number". Also, the "from the wall" number may include vampire losses. In my P85, I have found the from the battery number for rated miles to be 290 Wh/mi, and into the battery from a DC source (Supercharger) to be 300 Wh/mi. From the wall (AC), the rated mile number is 333 Wh/mi.

For the P85D, from the battery, that would be 290 Wh/mi * 265/242 or 318 Wh/mi. Both the 290 Wh/mi and the 318 Wh/mi are about what I seen on the energy graph screen of each car.

The P85 "from the wall number" of 333 Wh/mi * 265/242 is 365 Wh/mi for the P85D. Almost the 380 number but not quite.

 

[Bighorn]

The 380 Wh/mi on the EPA sticker is a "from the wall" number and not a "from the battery number". Also, the "from the wall" number may include vampire losses. In my P85, I have found the from the battery number for rated miles to be 290 Wh/mi, and into the battery from a DC source (Supercharger) to be 300 Wh/mi. From the wall (AC), the rated mile number is 333 Wh/mi.

For the P85D, from the battery, that would be 290 Wh/mi * 265/242 or 318 Wh/mi. Both the 290 Wh/mi and the 318 Wh/mi are about what I seen on the energy graph screen of each car.

The P85 "from the wall number" of 333 Wh/mi * 265/242 is 365 Wh/mi for the P85D. Almost the 380 number but not quite.

My from the battery rate is 275Wh/rated mile now--this has changed with time. That's how I've extrapolated the P85D to ~306. There's a little noise around that insofar as I see 74kWh available from a range charge and one P85D has seen 76.8 (317), I think. Also rated range charges have gone as high as 246-247.

The fact that the factory sticker shows 380 Wh/m for both cars seems suspect based on early results.

- - - Updated - - -

I don't ever recall tesla or anyone else claiming the staggered 21" on the P85+ was more efficient then the standard 21" of the P85. If anything, it would be less.

The website said that when I ordered mine. I believe it was predicated on the PS2s.

 

[kennybobby]

Hmm... a good side by side coast in neutral might be a nice additional to this test, down a hill on the interstate. I'll try to work that in.

If you could do it on a flat without incline would take out another factor. Both at 65 then go to neutral and coast, start a stopwatch when speed hits 60 and stop timer when speed hits 40,45, or 50. From the coastdown time, knowing weight and Cd x A, can calculate Crr for those tires.

 

[AWDtsla]

The 380 Wh/mi on the EPA sticker is a "from the wall" number and not a "from the battery number". Also, the "from the wall" number may include vampire losses.

So any charger efficiency increases mean this number gets better. Did anybody check the P85D?

 

[Chris_WDO]

Tried this... it doesn't seem to want to stay for some reason. Actually, I think my suction cup mount is broken, and I only have one.

Ah ok....of course, if there's any way air can get under the suction cup, then theres no remedy but to replace it.

One step worth trying though (if not already done yet) is to thoroughly clean both window and suction cup surfaces with 94% alcohol on a fresh, clean piece of cloth, and let both dry thoroughly. If it still does not work, it most certainly is due to a broken suction cup.

 

[wk057]

Leg one done.

Results so far are as expected. Oddly enough the P85 and P85D don't agree on range traveled so far. 56 and 55.5 miles respectively. This could explain why I couldn't perfectly follow with cruise control.

So far 313 Wh/mi P85, 365 Wh/mi P85D.

FLIR shows no major heat difference in our tires or rotors or anything else.

More soon. Getting food.

 

[breser]

The 380 Wh/mi on the EPA sticker is a "from the wall" number and not a "from the battery number". Also, the "from the wall" number may include vampire losses. In my P85, I have found the from the battery number for rated miles to be 290 Wh/mi, and into the battery from a DC source (Supercharger) to be 300 Wh/mi. From the wall (AC), the rated mile number is 333 Wh/mi.

It includes vampire losses. There are required rest periods where the car has to sit. Vampire loses would show up to some degree in those.

 

[dsm363]

There is another thread about this but Tesla has a new blog post up about this

 

[Andyw2100]

There is another thread about this but Tesla has a new blog post up about this

Blog post here: Driving Range for the Model S Family | Blog | Tesla Motors

Reader's Digest version: software update coming by end of January to give P85Ds the expected range.