Regenerative braking versus ICE engine braking

[SwampNut]

I have no idea why I don't have a useful memory of this.  I guess because it's just such a normal function of a bike, it just sits in the background.  In a discussion on an EV motorcycle forum, someone claimed that regen braking was "a lot" more powerful than engine braking, and you have to be more careful with it in turns with aggressive riding.  My gut tells me this is not true, at least in a vast, general sense and probably not "a lot."  It's sure to vary by bike just like it would with ICE.  Motor controllers have much lower regen capability than they do power capability, and I don't know why.  My bike can do many hundreds of amps of acceleration, but only 80a regen.  My hub-drive electric bicycle has around 150a drive and something like 30a regen (can't remember exactly).  Of course in ICE you have a bit of a difference between a high-compression sport liter bike and a low-tune beginner 650.

 

What do you all think?  We can test this.  Just need to put a couple bikes side by side.  TFT, do you have your XX in AZ?  I can't remember.  Maybe if you bring it for the LIDAR test with Mike, we can do a lot of data gathering.

[SwampNut]

To be clear on one point; I have a vague notion of why regen is less than acceleration.  I just don't fully understand it.  Maybe @mikesail has more to say on it.

 

Batteries generally don't want to be charged as quickly as they can provide power.  And I'm not sure on the internal configuration of the actual devices in the motor controller, but I would guess they aren't just reversible; they likely have a number of components that only do one direction or the other.

[superhawk996]

The reason your Zero doesn't give more regen braking is because you always forget to downshift.

 

The Zero's top speed is 124, about what a Bird does in 3rd so it would be interesting to test braking just in third vs. being able to downshift.  My guess is that the Bird will out-brake it at high speed and the Zero would beat it at lower speed.  57.8MPH will be the crossover point...you know, for when we start betting.

 

It would also be interesting to do a roll-on drag race between them using only 3rd gear.  The Zero would initially leave the Bird, but would the Bird build power quickly enough to catch up?

[IcePrick]

[SwampNut]

4 minutes ago, superhawk996 said:

The reason your Zero doesn't give more regen braking is because you always forget to downshift.

 

The Zero's top speed is 124, about what a Bird does in 3rd so it would be interesting to test braking just in third vs. being able to downshift.  My guess is that the Bird will out-brake it at high speed and the Zero would beat it at lower speed.  57.8MPH will be the crossover point...you know, for when we start betting.

 

It would also be interesting to do a roll-on drag race between them using only 3rd gear.  The Zero would initially leave the Bird, but would the Bird build power quickly enough to catch up?

 

All good questions.  Regen versus just air braking at high speed is hard to quantify.  If there's a specific current limit, then the regen effort (watts) should drop as the speed drops, I think.  Voltage should go down.  In this case, it should brake more at higher RPM.  Regen is in fact totally gone at very low speeds, such as coming to a full stop.  They warn you about this in the manual.

 

[mikesail]

4 hours ago, SwampNut said:

To be clear on one point; I have a vague notion of why regen is less than acceleration.  I just don't fully understand it.  Maybe @mikesail has more to say on it.

 

Batteries generally don't want to be charged as quickly as they can provide power.  And I'm not sure on the internal configuration of the actual devices in the motor controller, but I would guess they aren't just reversible; they likely have a number of components that only do one direction or the other.

The controller certainly doesn't need to care, it is a symmetrical circuit. The fundamental switching elements don't care which way the current is flowing. Cell charging limitations are likely in play though.

 

Here's a fun fact to consider, the braking energy from aero drag is pretty much exactly what your motor is putting out at a given speed.

So a bird at full tilt boogie will aero brake at well over 130 hp, pretty significant deceleration.

[tomek]

5 hours ago, mikesail said:

 

So a bird at full tilt boogie will aero brake at well over 130 hp, pretty significant deceleration.

Well, HP=F x V. F is rolling resistance plus aero drag. V velocity. But, yes, at high speed lion's share is aero drag. And, if you were tucked in, and then roll off and sit straight up aero brake can be higher than engines peak HP.  That's why you never ever get directly behind someone when braking from high speeds on the race track. Even if your name is Marquez the guy in the front of will put brake you, and boom.