So I was watching Now You Know on Youtube and Jessie said something about using the motor regen to direct to a strip heater when the battery is too cold to take the charge (for cabin heat or to heat the battery). So why not have a “brake pipe” (electrically shorted pipe or finned metal strip) that takes all of the current that the battery can’t take? Does anyone know what the max power the motors can regen and what the max power the battery can charge from regen is? If the brake pipe takes all the heat you could race will smaller lighter brakes and they would last longer. Also the pipe could get much better airflow and you would not need to duct air to the brakes.
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Strip heater heat sink for performance braking, why or why not?
- Thread starter dww12
- Start date
NeverFollow
Active Member
I don't think that true for the cabin.
The rear electric motor is only used to heat up the battery when required.
Daniel in SD
(supervised)
How can you get 120kW supercharging then?
Converting electricity into heat is not complicated or expensive: Goodman HKP 20C 19 5 Kilowatt Heater Coil 68 200 BTUs of Heat
You can buy 32kW instant water heaters at Home Depot (EcoSmart 36 kW 240-Volt Self-Modulating 6 GPM Electric Tankless Water Heater-ECO 36 - The Home Depot). I posted a thread and the most plausible theory as to why they didn't put a resistive coil to capture regen energy was to cut costs. I've heard the the motor can dissipate power into the cooling loop but I haven't heard any numbers about how much power. I wonder if there is a limit of how fast you can safely heat the batteries?
This a what if, not a is it.
Ok so if max regen is 60kw and max power from both motors is 340kw, can the motors regen 340kw? Or more if output is limited by the battery?
Power for a 1g stop is P=m*a*v.
27.78m/s * 1847kg * 9.8m/s = 503kw
That leaves 440kw for the rotors or the “heat pipe” to take if the motors could take 500kw.
Ok so if max regen is 60kw and max power from both motors is 340kw, can the motors regen 340kw? Or more if output is limited by the battery?
Power for a 1g stop is P=m*a*v.
27.78m/s * 1847kg * 9.8m/s = 503kw
That leaves 440kw for the rotors or the “heat pipe” to take if the motors could take 500kw.
Daniel in SD
(supervised)
Why bother designing a system of capturing energy for braking rates that rarely occur? I don't think you would ever be able to eliminate the hydraulic friction system. To me the most logical thing to do is to use normal levels of regen energy to heat the battery when it's cold.
SSonnentag
埃隆•馬斯克
It depends on which component is overheating. If it's the AC to DC converter, the heat strip wouldn't do any good. I find it unlikely that the battery pack itself is overheating since superchargers dump juice into the battery pack for long periods of time at rates above what regen can do.
Daniel in SD
(supervised)
Maybe. I don't know much about motor controllers. Obviously they can handle 300kW+ converting DC-AC. I have no idea what it can do AC-DC.
Another thing to consider - Once you have enough regen capability to drag a tire, what do you do? You can't use ABS to un-drag it. You have to reduce regen and do it quickly. If you're tracking should the driver modulate the throttle pedal to stop the skid? Seems not natural. Usually you let off the accelerator when a car enters a skid.
So you would have to program regen into the brake pedal operation. I don't think Tesla does that. On purpose.
So you would have to program regen into the brake pedal operation. I don't think Tesla does that. On purpose.
For the track. The brakes have been a limiting factor, because of heat. Only an EV could transfer and dissipate brake heat to another heat sink (electrically). A heat sink that isn’t rotating (mass), could get a lot hotter without issues and could be in a better position to be cooled. It also would not warp and require replacing, so tracked 3s would require the same brake maintance as non tracked 3s, zero.
Daniel in SD
(supervised)
You could easily add ABS to regen. I think one pedal driving would be fine. And it would act as a deadman's switch to safely bring you to a stop!
Daniel in SD
(supervised)
The motor and inverter would require more cooling and you can't get them nearly as hot as a brake rotor. It's much easier to just put in bigger rotors and more ducting to cool the brakes.
It will be interesting to see how much regen they can get on the New Roadster.
That is the max regen that is allowed at that point in time. It changes based on SOC, temperature, how much regen has been done recently, etc.
A recent Bjorn range test video showed the regen limit warning coming up while he was going down a long hill while the SOC was still low enough to allow full regen.
My guess is that Tesla limits the time that you can spend charging/regening above a certain level...
For fun with some estimated numbers:
50kW Regen
30 kg coolant (~8 gallons)
3.31 kJ/kg*C specific heat (50/50 glycol coolant)
Temperature rise in the coolant would be ~0.5C per second. Not bad for periodic breaking, but may overwhelm with track braking or slowing down a mountain pass.
Daniel in SD
(supervised)
Yep, that was probably the motor controller or motor overheating.
So why not use it heat the battery cold conditions? That is the mystery.
AlanSubie4Life
Efficiency Obsessed Member
Probably time for someone to get out their VBOX and just answer this max regen question! Easy enough test to do... Based on my butt accelerometer compared to the Spark EV (which provides the readout for regen), and taking into account the added weight of the Model 3, I'd be mildly surprised if the max regen in an AWD was less than 60kW in the "no dots" scenario.
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