Comment by aitchnyu
14 hours ago
Tangential, how much regen can this system support?
For example, can a car with 200kW propulsion have a 400kW regen (Tesla has upto 65) and are cost effective like friction brakes?
14 hours ago
Tangential, how much regen can this system support?
For example, can a car with 200kW propulsion have a 400kW regen (Tesla has upto 65) and are cost effective like friction brakes?
All motors are generators. It's only a matter of how you are creating the magnetic field with the stator windings.
In order to generate a higher regen, you'd have to somehow get more energy in the motor first... and since its only rated for 200kW, good ol' physics limits you, IF thats all the energy you put into the system.
If you roll it down a hill, or do something exotic like inverting the magnetic fields .... you can exceed the motor rating. But thats usually not recommended because the motor driver itself isnt rated to handle that power.
In general the rating of a motor is about heat dissipation, which in turn is a function of efficiency. What this means is you can exceed the rating by "some amount" for "some amount of time". Many motors are rated for not what they can deliver, but what they can deliver continuously without overheating, but you can get a lot more power out of them for a short time.
You're also ultimately limited at the point where the tires lose grip and start sliding. Which can vary a lot based on road surface and conditions.
Their founder/CTO discusses that here and their ability to match the braking power density of carbon ceramic brakes: https://youtu.be/B2Hl4c1iZK0?si=bCLQnfovjY7t-eYm&t=900
400kW regen is going to be a fairly alarming level of stopping for a normal vehicle. It's OK to leave emergencies to the friction brakes.
The idea is deleting the friction brakes entirely, saving costs, maintenance and weight.
And 400kW isn't really all that much for a sports car. I remember 911 ads from the '80s that boasted "brakes with more than 1000 horse power".
So how do you stop then if the batteries are (close to) fully charged? You'd need to shunt that power into a big resistive load, and then dump that heat.
2 replies →
> can a car with 200kW propulsion have a 400kW regen
At the motor level it should be the same, in propulsion you’re converting current to torque and in regen you’re converting torque to current, with the same hardware. The high voltage wiring is the same and will set the same limit on current regardless of direction.
I believe bidirectional inverters are generally symmetrical as well, so that should not be a factor.
Which I reckon leaves two factors:
1. Battery C rates, afaik pretty much all chemistries have a higher discharge rate than charge rate, especially when trying to maintain them for a long time, so by that account regen power would at most be the same as propulsion (if the entire power train is sized for the battery’s charging rate).
2. Artificial limitations, obviously you could always artificially under-prop, though that seems unlikely outside of niche applications.
tldr: I don’t think so, except on a technicality (that you can artificially hobble propulsion).
How far fetched is the idea to use Super-Capacitors to take up the energy generated by braking and then slowly feeding it to the battery at a rate that it supports?
The energy density on super capacitors is pretty bad. If you imagine full power 200kW braking for 5 seconds that's 1 mega joule and at a best case 8 watt hours per liter you're going to need 35 liters minimum. Really you probably need to double that so you can float up and down and never fully saturate the capacitor as power inflow is going to drop as you get closer and closer to fully charged.
https://en.wikipedia.org/wiki/Supercapacitor
Am I reading you right that breaking power (that you want to regenerate in the system) >> speeding power? Obvious now I come to think of it, and still pretty nifty new thing learned if true!