Questions on MPIII power generation

[Middles Nowhere]

G’day all, new guy here with a few questions.

First I’d like give a big thumbs up to this forum for answering almost all of my question with your past threads. I’ve been lurking around here for a while as I built my first E-bike and the info has been very helpful.  Thanks All!

Now my questions, I’ll try to not write an essay:
 
Will a 48v MPIII  hub motor always generate energy when the wheel is turning without battery power to the motor and regen switch off?  If so, where is the energy going if my battery is not connected to absorb the electrons (both line and ground isolated), heat conversion I’m guessing? Will the heat build-up eventually transfer to the internal controller electrics and cook the controller over time?

I’ve been testing out my motor install (bike in situ, upside-down, no battery and hand turning the crank) to make sure noting is binding. I noticed the hub was a bit warm after a couple minutes of hand cranking. There was almost no resistance from the hub motor so regen was not engaged. I hooked up a multi meter to the motor wires and found  the motor is generating up 20+ volts power under hand crank input. Battery is disconnected, regen switch is off and the brake switches are unplugged from the harness. I somewhat understand the power generation effect on loaded electric motors, but if I need to disconnect my battery for whatever reason and ride my bike under my own power for a longish distance (lets say 25kmh at 20km distance) will this eventually fry the controller?  Will grounding a motor wire (ground or line) to frame absorb the kinetic heat?

Thanks everyone...your knowledge, ideas and general input is appreciated 

[Morgen 3Eman]

Hi Mid...

As it turns out, a voltage is generated whenever a conductor is moved through a magnetic field. What happens to the power generated is determined by whatever circuitry it is connected to. Without control power, your MP3 is actually in a regen mode.  My guess is that the control circuitry is powered up by the generated power.

I'll be surprised if Alan doesn't have a technical description that is useful to you....

Welcome to the group.

TTFN,
Dennis

[Bikemad]

No technical description as such, but I did document a similar finding on my original Magic Pie.

I haven't tried this on the MPIII or Smart Pie, so I don't know whether the newer controllers allow the voltage to rise quite so high, but I did however experience the regen braking force cutting in on my Smart Pie when I originally tested the bike down the road and back (before the battery had been fitted) and applied the brakes at around 20mph.

The current/voltage being generated by the windings is able to flow in a reverse direction through internal diodes inside each of the controller's MOSFETs, even though the MOSFETs PWM duty cycle remains at 0% (100% switched off):



Alan
 

[Middles Nowhere]

Thanks for the insights...sometime soon I'll be breaking open the piggy bank for some high lumen LED lights. I think I will set up connectors that allow me to hook them into the hub motor wires if I need to disconnect my battery. Better safe than sorry, I much rather have the LED's eat the regen juice than risk blowing my controller.