. . . Inductance Motor / Regenerative Braking . . .

[The7]

I'm hoping that someone will check my math and find that I've made some sort of gross error. The big point here is that if you want to get the necessary braking force to skid the tires (a full 1G's worth of braking energy) and you have a 125 kg bike and rider combination then it appears that you need to produce 8 horsepower's worth of braking. (6250 watts)

8 horsepower is a lot!!!

Hopefully someone can redo the math and find I'm totally wrong on this...

OK. I use the energy approach.
Energy E = 1/2 m (V*V)
= 1/2* 125 (10*10) = 6250 jouls

To stop this ebike in 1 second, the power required is E/t
= 6250 J/s = 6250 watts

To stop this ebike in 4.2 seconds, the power required
=6250/4.2 = 1490 watts

If you use an power of 1490 watts to accelerate the ebike from 0 m/s to 10 m/s, it will take 4.2 second.

The energy approach answer is consistant with your SAFE answer.

 

[safe]

If you use an power of 1490 watts to accelerate the ebike from 0 m/s to 10 m/s, it will take 4.2 second.

The energy approach answer is consistant with your SAFE answer.

This is one of those times that I really had hoped to be wrong...

So regenerative braking as a concept seems seriously flawed on an electric bike. If you were to scale things up to the size and weight of a motorcycle then the braking forces would also increase and by then you might be looking at a requirement of 100 horsepower to stop a motorcycle. (since it weighs 600 lbs)

With these numbers a 750 watt motor with typical bike and rider weight conditions will take a regenerative braking force 8 times that to get the job done.

Any last ditch ideas to save "regenerative braking" as a concept?

(if you are only capturing a fraction of the braking energy it's seems a waste of effort)

 

[billvon]

>Any last ditch ideas to save "regenerative braking" as a concept?

Short the phases of a PM motor. You'll get a lot of braking and won't need a controller to do it! Alternatively just use a variable resistor (a very large variable resistor.) Locomotives do something like this; they have huge resistor grids to dissipate the power.

 

[fechter]

All that energy has to go somewhere. At high loads, you run into the same physics that happen when it's a motor. The I2R losses will cause about half (or more) of the energy to be dissipated in the motor windings. The rest of the energy has to either go into the batteries or into a gigantic resistor. If you completely short the windings, then all the energy is dissipated in the motor.

For flat ground, doing a high current 4.2 second brake is not going to overheat anything. On a long hill, it's another story.

You could overheat the motor going downhill. Forced air cooling will help. If you current limit the regen, you can keep the system more efficient and reduce the motor heating dramatically.

I have some hills around my house that I have no problem going up, but my brakes will fade going down. Regen is good for this kind of condition.

 

[safe]

All that energy has to go somewhere. At high loads, you run into the same physics that happen when it's a motor. The I2R losses will cause about half (or more) of the energy to be dissipated in the motor windings.

This is valid for a permanant magnet motor, but for an inductance motor the efficiency goes up with larger loads. I'm sure there's a point where you begin to overload the inductance motor too and cause higher heating, but I'm not sure if it's to the same degree.

What it really comes down to is the ability of the motor to adapt well to loads that are EIGHT times the normal load.

Is the Inductance motor able to do this?

We know the permanent magnet motor is very closely tied to a rigid powerband shape and there's next to nothing you can do to change anything. The permanent magnet motor simply can't do it very well. (and we are okay with this) The inductance motor seems more able to deal with drastically variable load demands.

Remember.. it's 1hp for forward motion and 8hp to stop.

Hard braking only happens for a short period of time. By my previous calculation you only need ONE SECOND of 8hp braking to bring a bike to a stop from 20 mph. If you gradually brake on a hill you might only be using 1-2 hp which might not be a problem. The big question is the "peak load" of 8hp... what could handle such a thing?