HaulingAss

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If you can break the tire fre in acceleration, you can skid when decelerating.

Your friction brakes can heat up and glaze, too, Hardly an excuse not to have them.

-Crissa
I was saying the car cannot break traction under acceleration in a straight line, not at speeds that one might need to stop suddenly.

Modern cars have capable brakes that won't glaze in one emergency stop.





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Cybr on

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982 Km.. woah!
Right? My mind is 🤯
Please let it be over 600 +mile range. That would be perfect for trips that take us miles away from main road. Add in the solar tonneau cover and I’m plaid.
 

JBee

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In normal use, braking is required at all speeds, from the top speed of the car all the way to zero. Why do you think the power transistors can handle significantly more power than they were designed for? They have thermal limits for reliability/cost reasons. Exceed those and they start failing.

It's simply not practical to expect components designed to accelerate the car to also brake the car which would not only greatly increase their duty-cycle but would impose higher loads than peak acceleration would.
I will repeat this statement for the third time:
The plaid already accelerates faster with electric motors than it can decelerate with it's "sporty" friction brakes.

This means that all components in the drivetrain, except the charging C rate of the battery used (as discussed separately), but in particular including "power transistors" are capable of sustaining that level of acceleration and deceleration. In fact by the very nature of the controller driving both the PM and IM have regen braking already, and also go in reverse btw. The regen limit is the batteries not in any way the "transistors". No modification or upgarde required.

Despite this induction retardation also works as per previous link, and is already used in trucks and buses and has been for decades.
This brake is frictionless, does not even need a complicated controller let alone any form of battery.
 
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ajdelange

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I'll just point out that the induction retardation system is a generator connected to a dump load with the dump load built into the rotor.

I'm not really understanding the arguments about the transistors but note that a 2500 kg vehicle traveling 80 mph has a kinetic energy of 878 kWh. If you want to dissipate that in 10 seconds (slow the car to a stop) you have to be able to pull power out of the car at a rate of 316 kW. The motors and inverters in my X can handle that much but I can't put that much into the battery. That means I'd need a dump load that could handle 800 kW. Not that I have ever had to do this but obviously the "dump load" is the friction brake and the real message of this post is that you would waste almost 1% of you battery if you did slow your car from 80 mph to a stop by any means other than the use of regen at a 77 kW rate.
 

JBee

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I'll just point out that the induction retardation system is a generator connected to a dump load with the dump load built into the rotor.

I'm not really understanding the arguments about the transistors but note that a 2500 kg vehicle traveling 80 mph has a kinetic energy of 878 kWh. If you want to dissipate that in 10 seconds (slow the car to a stop) you have to be able to pull power out of the car at a rate of 316 kW. The motors and inverters in my X can handle that much but I can't put that much into the battery. That means I'd need a dump load that could handle 800 kW. Not that I have ever had to do this but obviously the "dump load" is the friction brake and the real message of this post is that you would waste almost 1% of you battery if you did slow your car from 80 mph to a stop by any means other than the use of regen at a 77 kW rate.
Adjelange I think either your units or numbers are out. Should be around 1kWh. Remember the battery isn't big enough (878kWh) to accelerate to 80mph otherwise! :)

Also the eddy currents in the discs slow the induction retarder down, so not really a dump load or a geny. Would be nice to make it work in reverse though, heat to kinetic rpm!
 
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Crissa

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Modern cars have capable brakes that won't glaze in one emergency stop.
The same is true of the motors. They won't normally reach that temperature except with repeated heavy use.

And no, I don't know why you think the motor can't break the tire loose. My 11kW motor can break the tire loose on my motorcycle if it didn't have the limiter built into it, and it can definitely break the tire loose decelerating via regen which is why they have regen so limited on my bike.

Tesla has a much more powerful setup.

And the Taycan, as I linked, already does this, by having banks of capacitance and resistance to continue using regen instead of the friction brakes in heavy use.

-Crissa
 

ajdelange

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Adjelange I think either your units or numbers are out.
Wouldn't be the first time. Let's check.
v = (80*1.6*1000/3600) = 35.5556 m/S
m*v^2/2 = 2500*(80*1.6*1000/3600)^2/2 = 1.58025e+06 joule = 1.58025e+06 watt seconds = 1.58025e+06/3600 = 439 Wh. So I forgot to divide by 2, interpreted Wh as kWh and was too lazy to think about whether the result made sense!

Better check the power calculation too. P = p*a = 2500*(80*1.6*1000/3600)*1*9.8 = 871 kW for 1 g decelleration. As the X can only take about 80 kW regen it's clear that the max we can do at 80 mph is less than 0.1 g (about 1 m/s/s)


Also the eddy currents in the discs slow the induction retarder down, so not really a dump load or a geny.
I'll argue that in broad terms it is. In a diesel electric locomotive a magnetic field moves relative to some coils inducing current flow in those coils which current is routed to a resistor bank. In this device a magnetic field moves relative to some coils in which a current is induced which current results in the dissipation of heat in the coils themselves. In this case, though , the "coils" are the eddy loops in the conductive material of the rotor itself.
 

JBee

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Ok those numbers sound better, as well as the units ;-)

So we need 871kW to do 1g braking on a MX. But current battery tech (18650?) in MX only allows for 80kW regen. How fast can your MX charge at a supercharger? M3 is 250kW but with a 75kWh battery using 2170s?

So if a TM has a 200kWh pack we chould be able to see 2.6x that so 666kW if it was a 2170 cell pack. Thats already getting close to 871kW. With the 4680 cell they were talking about 5x reduction in resistance due to the tabless design. Even if its "only" 2x at 1300kW we're already there and above on a CT for full regen braking.
 

ajdelange

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The interesting thing about my MX is that it charges at about 1 C i.e. around 100 kW AVERAGE. Upon arriving at an SC with low SoC it will, initially, charge much faster than that but on average it charges at 100 kW. Nevertheless the maximum regen is 77 kW for this car. We can, of course, speculate all day about how fast the CT may take regen charge and the basic a = P/p formula will tell you how fast you can slow down (in m/s/s; divide by 9.8 for g) for whatever numbers you want to guess for mass and P (charge rate).

But none of this bothers me. Friction brakes aren't going away. What does trouble me is that I can't figure out how a motor that is turning at a slow speed can generate enough voltage to push any current into the battery at any rate. The only thing I can think of is a DC/DC converter after the rectifier. I know full well that the car is using regen to brake down to very low speed because I can see it on the power meter.
 

HaulingAss

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I'll just point out that the induction retardation system is a generator connected to a dump load with the dump load built into the rotor.

I'm not really understanding the arguments about the transistors but note that a 2500 kg vehicle traveling 80 mph has a kinetic energy of 878 kWh. If you want to dissipate that in 10 seconds (slow the car to a stop) you have to be able to pull power out of the car at a rate of 316 kW. The motors and inverters in my X can handle that much but I can't put that much into the battery. That means I'd need a dump load that could handle 800 kW. Not that I have ever had to do this but obviously the "dump load" is the friction brake and the real message of this post is that you would waste almost 1% of you battery if you did slow your car from 80 mph to a stop by any means other than the use of regen at a 77 kW rate.
A 10 second stop from 80 mph is not traction limited braking on dry pavement. It's not fast enough braking to safely replace friction brakes.

Any electric replacement for friction brakes will need to have at least four requirements to gain approval:

1) Capable of braking each wheel independently.
2) Capable of traction limited braking at all speeds and on all surfaces.
3) Redundancy in case of failure of electrical components.
4) capable of braking down to zero mph

Until these things are achieved, and at a cost approximately in the ballpark of the best friction brakes, friction brakes aren't going anywhere.
 
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HaulingAss

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The same is true of the motors. They won't normally reach that temperature except with repeated heavy use.

And no, I don't know why you think the motor can't break the tire loose. My 11kW motor can break the tire loose on my motorcycle if it didn't have the limiter built into it, and it can definitely break the tire loose decelerating via regen which is why they have regen so limited on my bike.

Tesla has a much more powerful setup.

And the Taycan, as I linked, already does this, by having banks of capacitance and resistance to continue using regen instead of the friction brakes in heavy use.

-Crissa
Crissa, please read what I wrote. I said the motor cannot break the tires loose at all speeds, only slow speeds. If used in a regenerative fashion it also has to be capable of modulating the braking force very rapidly, as modern anti-lock brakes do.

I don't know why some of you seem to think friction brakes (as emergency necessities) are going away. Not in the next 20-30 years and maybe not in 50 years.

I love regen and will love the more advanced regen that is coming down the technology pipeline but friction brakes make a lot of sense as an emergency backup. They are also used as a parking brake.
 

HaulingAss

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But none of this bothers me. Friction brakes aren't going away. What does trouble me is that I can't figure out how a motor that is turning at a slow speed can generate enough voltage to push any current into the battery at any rate. The only thing I can think of is a DC/DC converter after the rectifier. I know full well that the car is using regen to brake down to very low speed because I can see it on the power meter.
Even taking into account that the electric motor is spinning a lot faster than the wheels are turning (due to gearing)? And taking into account that regen braking goes away completely somewhere just under 5 mph?
 

HaulingAss

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I will repeat this statement for the third time:
The plaid already accelerates faster with electric motors than it can decelerate with it's "sporty" friction brakes.
Not at all speeds. Any replacement for friction brakes has to work well at all speeds. This is non-negotiable with me and with the regulators.
 

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