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Perhaps I should describe what I mean by road racing..

Son, I spent my youth reading Car & Driver, Road & Track, and watching racing legends at Elkhart Lake-Road America in the 1960s, and early 1970's. In 2010 I watched history being made at the TTXGP at VIR. :giggle:

My wife and I are in this video.

 

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Discussion Starter · #22 ·
Good! Not everyone does! When I tell some people I road race, they think Fast and Furious blowing through city streets.
 

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Road racing is perpetually fascinating, while street racing was cool when I was 16 and dumb :]

Does anyone know what normal operating temps are for the battery? Are high battery temps the cause for the Bolt to enter "Low Propulsion" mode? When I was at a track day at Thunderhill (West), when I got to about 50-60% SOC that was when I'd get that warning, so I thought it was due to that. I had not known about high battery temps. I think that day it was in the low 90's but pretty windy as well.

It looks like there's a radiator & fan under the hood like normal cars - does battery coolant flow through there? Is there value in increasing the size or better design of radiator + upgrading to a more powerful fan?

Fender rolling for the Bolt seems difficult with the plastic trim, I've wondered if it could be removed and fenders modified for wider wheels/tires.

It's interesting that the Bolt is mechanically limited at 94mph, I had thought it was software. Since electric motors have an almost flat torque curve, would it be possible to put a higher gearing to obtain higher top speeds without sacrificing low-end acceleration too much?
 

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It looks like there's a radiator & fan under the hood like normal cars - does battery coolant flow through there?

Fender rolling for the Bolt seems difficult with the plastic trim, I've wondered if it could be removed and fenders modified for wider wheels/tires.

Since electric motors have an almost flat torque curve, would it be possible to put a higher gearing to obtain higher top speeds without sacrificing low-end acceleration too much?
The radiator and fan are for the power electronics. The battery is cooled by the AC chilling the normal antifreeze in the battery coolant loop.

Too bad there is aluminum behind that plastic. Otherwise there would be a perfect aftermarket for wheel well flairs.

Bolt 3.jpg

It would increase top speed, and the acceleration could be almost as strong. The problem would be the increase in amp load/heat under acceleration, which would probably make it throttle back even sooner.
 

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Discussion Starter · #25 · (Edited)
What I mean is the top speed is limited by the gearing selection and the maximum allowable RPM of the rotor in the motor; that would be software controlled. It's the same thing as a modern ICE, there is an RPM limiter in the ECU that cuts fuel and/or spark.

So if the car runs out of engine RPM before the drag load maxes out the power output of the engine, then it is gearing limited. If the car runs out of power to overcome drag before it hits max engine RPM, then it is drag limited.

Eventually people will hack the engine control system and be able to overspeed the motor in order to increase top speed. Someone will eventually find the motor's RPM limit the hard way.

I am OK with the current gearing since the acceleration is great for city and highway. The top speed would only be too slow on faster race tracks, like CoTA or Brainerd.
 

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Discussion Starter · #26 ·
On the fender rolling, only the portion at the top of the wheel well needs to be rolled since the tire moves vertically with suspension compression. I was feeling the edge on the back of the front fender this evening and there is a significant protrusion there.

Attaching the fender trim with trim tape would work, and then the rear bumps/holes/fasteners seen above in GJetson's image (thanks) would no longer be needed. Trim tape is seriously strong if both surfaces are prepared correctly.
 

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So it seems maybe the mini-evaporator (battery chiller) in the battery coolant system could be upgraded then, or the A/C condenser, or both.

From the video it seems like battery coolant loop is:
  1. Surge tank
  2. Water pump
  3. Battery coolant heater
  4. High voltage battery
  5. Battery coolant chiller
  6. (Back to surge tank)
The battery coolant chiller allows heat transfer from the battery coolant to the A/C refrigerant, where the refrigerant runs in a separate loop through a condenser. When the refrigerant passes thru the chiller, it evaporates due to the heat from the battery coolant, thus "cooling" it.

So if you can increase the surface contact area of the interface between the battery coolant and A/C refrigerant within the battery chiller, you can increase heat transfer. It's possible that running larger A/C refrigerant lines for a higher volume could help too. I know in HVAC mini-split heat pump systems, you have larger diameter lines for larger condensers/air handlers for higher cooling BTU's.

Additionally, if you increase surface area (fins) of the A/C condenser as well as air flow (higher CFM's using a more efficient/powerful fan) across that surface area, you can increase heat transfer from the A/C refrigerant to the outside air.

Because the condenser is right in front of the radiator, I wonder if we'd see any types of gains just by upgrading the fan, even by a degree or two. Perhaps hood vents could help move all that hot air to the outside more efficiently as well.
 

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So it seems maybe the mini-evaporator (battery chiller) in the battery coolant system could be upgraded then, or the A/C condenser, or both.
@Telek has made the point that the problem with people's schemes for increasing the heating/cooling of the battery pack is that they will exacerbate the poor temperature gradient control of the pack design.
 

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@Telek has made the point that the problem with people's schemes for increasing the heating/cooling of the battery pack is that they will exacerbate the poor temperature gradient control of the pack design.
So some cell groups will get better cooling than others? Does it become more dangerous or detrimental for that to happen?
 

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So some cell groups will get better cooling than others? Does it become more dangerous or detrimental for that to happen?
Not some cells better than others. One end of each cell will be much cooler than the other. Not good for the life of the cell. The Bolt needs a cooling manifold on top of the pack, with the aluminum plates between cells extending out, and a tab bent to contact, like on the bottom. The best setup would be actual liquid carrying plates, like in the Volt pack.

1623012651293.png
 

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I see, so then the cells are placed vertically, with each taking up the full height of the pack? I would be interested in seeing how Formula-E packs are built and cooled.

Looks like Formula E packs are 54 kW, of which I imagine they use all of during the race before switching to their second car. So maybe it is the battery temps and not SOC that trigger "Low Propulsion Mode" in the Bolt.

Not a huge amount of detail in this video but interesting nonetheless:

I think in this article they are mentioning flooding the battery pack with a dielectric fluid rather than using cold plates as you've shown from the Volt: How to design a Motorsport Battery in 7 steps - Racecar Engineering

That seems like the ultimate cooling solution - battery cells in direct contact with the coolant with almost all of its surface area able to have heat carried away.
 

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So it seems maybe the mini-evaporator (battery chiller) in the battery coolant system could be upgraded then, or the A/C condenser, or both.

From the video it seems like battery coolant loop is:
  1. Surge tank
  2. Water pump
  3. Battery coolant heater
  4. High voltage battery
  5. Battery coolant chiller
  6. (Back to surge tank)
The battery coolant chiller allows heat transfer from the battery coolant to the A/C refrigerant, where the refrigerant runs in a separate loop through a condenser. When the refrigerant passes thru the chiller, it evaporates due to the heat from the battery coolant, thus "cooling" it.

So if you can increase the surface contact area of the interface between the battery coolant and A/C refrigerant within the battery chiller, you can increase heat transfer. It's possible that running larger A/C refrigerant lines for a higher volume could help too. I know in HVAC mini-split heat pump systems, you have larger diameter lines for larger condensers/air handlers for higher cooling BTU's.

Additionally, if you increase surface area (fins) of the A/C condenser as well as air flow (higher CFM's using a more efficient/powerful fan) across that surface area, you can increase heat transfer from the A/C refrigerant to the outside air.

Because the condenser is right in front of the radiator, I wonder if we'd see any types of gains just by upgrading the fan, even by a degree or two. Perhaps hood vents could help move all that hot air to the outside more efficiently as well.
I think the easiest solution is a tank of water under the hood (washer bottle) that sprays onto the condenser when placed under load or base upon battery temp. The Subaru STi did this exact thing for the intercooler.

Also, look the Model 3 team with Randy Pobst as the driver. They had all sorts of thermal issues because they modified the stock cooling system in the M3. The team running a stock M3 had no cooling issues.
 

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From what EV-MODS has written about his experience tracking the Bolt, the battery temperature remains relatively reasonable. He found the big power reduction came from elevated transmission and power electronics (same coolant loop) temperatures. The good news is, that is the system that is much easier to modify.

It would be interesting to log trans temp and power electronics temp in track, and see what kind of delta there's between them. If the coolant is hotter or the same as the trans, we could use a larger rad, or increase airflow somehow. But if the trans is significantly hotter, it means the heat exchanger plate is insufficient. Wouldn't be too hard to make a sandwich plate that goes between the oil pump and the transmission to send oil out to a seperate cooler and back.
 

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It would be interesting to log trans temp and power electronics temp in track, and see what kind of delta there's between them.
I will try to remember to take a screen shot next time I am out driving on the highway. As I recall the trans and motor were a lot hotter than the inverter. But this was also steady speed driving, not hammering out of corners.


driving screen.jpg
 

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Amateur EV track day and race cars are coming, no doubt. The National Auto Sport Association (NASA), a club-level racing group, is already working on amending the rules for EVs. For now they are placing EVs in the Unlimited classes where pretty much anything goes.

That puts them in some SERIOUSLY fast company as the front-runner TT cars are usually extremely fast cars with (more importantly) very fast drivers. Some examples from my region are 600+ HP dedicated track Corvettes with very sticky and very large Hoosier racing tires, and aerodynamics. Even Radicals (Radical Sportscars | Racing | Track Day | Road and Race Cars) are allowed. Clearly the current crop of factory EVs, even Teslas, are seriously outclassed in this field so they need a method for classing them in a competitive manner.
I think the Indy 500 cars this year are hybrids? Correct me if I'm wrong. Do they have the CVT transmission yet? Regular shifting takes time.

As for EV race cars, they will probably be in a separate class. They can blow ICE cars away, because they have high torque at low rpm. With ICE cars, it's the opposite-- high torque only at high rpm.
If I wanted performance out of my Porsche, I had to rev to 5000 rpm. That's where you get your money's worth in a Porsche. But you can't do that often around town without speeding. The car is meant for the track.

EVs are going to change the paradigm--in racing and everyday driving. Cop cars will have to be EVs. They won't be able to keep up with EV cars and trucks. All of this is coming in the next couple years.
 

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ICE cars, it's the opposite-- high torque only at high rpm
Well, not exactly I know what you mean but an EV can make maximum torque at 1rpm and continue making it to its maximum RPM. An ICE engine with a 6000rpm redline normally has maximum torque around 3500 RPM just about the time it stars making power. Torque then falls off and power climbs to peak power or redline. Those are not always the same.

Not all EV's are going to be fast.
 

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Discussion Starter · #39 · (Edited)
That Racecar Engineering article that @heisian linked to is great. FWIW Racecar Engineering is a high-end magazine that has been covering race car tech for a very long time, and it usually goes into significant technical depth not necessarily targeted at the layman. I had a subscription for years.

An eyeopener quote from the article:
"All in an effort to extract the maximum energy out of the battery for the lightest possible weight. Since 2007, the F1 ERS system has seen an 81% weight reduction, a 56% efficiency increase whilst achieving 12 times the power density and twice the energy density. It is this development drive to win in motorsport that will continue to change the face of battery technology as we know it."

Also the discussion on the pros and cons of bathed vs heat sink cooling in that article are interesting.

From @zbrown
"It would be interesting to log trans temp and power electronics temp in track, and see what kind of delta there's between them."
I agree. Though I have not used it for logging, maybe Torque has a way. I'll give it a look.

From @heisian
"Perhaps hood vents could help move all that hot air to the outside more efficiently as well. "
Hood vents usually work VERY well if they are in the correct location. They need to be forward of the windshield since the base of the windshield (depending on the car) is a high-pressure stagnation region; this is taken advantage of by cowl induction. At any rate I have hood vents on my LS1 Miata track car and they are indeed effective. A splitter, in addition to generating downforce, can also create a significant pressure region in front of the car's air dam which forces more air through the radiator. I also have a splitter on my car, a big one., though most of it is underneath out of view.

This is a side shot of my old track car in action; the new one is a little different but essentially works the same way. The hood vents are circled in red and the splitter is circled in blue.
35526


Ha whoops I reversed the colors, but same car...
35527
 

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Discussion Starter · #40 · (Edited)
Not all EV's are going to be fast.
Of course not, no more than all ICE cars are considered to be 'fast'. Keep in mind a car that is considered to be 'slow' like a stock Miata can whip the pants off of a car considered to be fast, like a Corvette. I've seen it happen over and over at the track. In fact it is a running joke that some guy in a $5K Miata can regularly make a guy in a $50K Vette look foolish if the Miata driver has skill and the Vette driver does not.

I remember that a racing friend of mine and I were listening to two students in very nice Porsches talk about their lap times with excitement. We snickered to ourselves because those lap times were 5-10 seconds slower than the times the great drivers were running in their Spec Miatas, which are relatively speaking, stock cars.

The point is, a car does not have to be 'fast' to be effective as a track car.
 
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