Regen braking: confirmed!

[BrianG]

I was doing a little playing around with my EZRun80 ESC the other night. I still need a motor mount, but I thought I'd get some data from an unloaded motor.

Before I go on, let me make the disclaimer that I do NOT suggest ever running a motor unloaded! Do so at your own risk!

I hooked a freshly charged 4s lipo pack and a Neu 1512/2d to the ESC. I also attached a Fluke 87A voltmeter to the battery wires (using a little adaptor I made). I then set the meter to "record mode" where it will take samples. In this mode, the meter will also record the min, max, and average readings. Nort sure what the sampling rate it though.

Remember, the motor is not attached to anything.

I gradually applied throttle until rpms were at max. Lipo voltage at this point was about 14.9v. Then, I jammed on the brake. When I looked at the meter's max voltage, it read 29.4v! Yeah, there's regenerative braking here, and quite a bit of it. Repeating the test gave me the same approximate result.

Then I asked myself "self, I wonder what the current is at that point?". I had to be careful here since my meter is only rated for 10A, so I changed the leads around so the meter was in series between the ESC and battery, and reset the recording mode. Again, I gradually increased throttle to almost max (to reduce current spikes), and then jammed on the brake. I measured -2.96A. Repeating the test got -1.82A. Yes, negative current. That's because my meter was set up to read current to the ESC, not from it.

Obviously, the spike is very brief and I am probably not getting the full reading due to my meter's sampling rate, but those are pretty hefty numbers from an unloaded motor, which means there is a LOT less momentum acting on the windings/magnet than there would be in a moving vehicle. I shudder to think what those poor caps and FETs deal with in a vehicle with a LOT more kinetic energy!

I wonder if all ESCs should have a transorb or something that would shunt any voltage no more than 10% higher than the cap ratings? These spikes, even as brief as they are, can't be good for components! IIRC, the MMM does have these devices which kick in at 26v, so that makes me feel a little better.

Anyway, just thought some would like to see real test results. If anything, this proves regenerative braking IS present, at least in the HobbyWing EZRun80, but the design is just like just about every other ESC on the market, so I think we can assume all the other ESCs act the same way.

And yes, motor and ESC are both still fine.