velias said:
After looking at the excel statistics, what do you think about the regenerative payback?
It averaged 2-3 percent.
I wonder if having regenerative capability in a controller is worth the extra circuitry?
Your question of "is it worth it?" is based on the common and incorrect assumption that extra or more complicated circuitry is required for a regen motor controller, but that is not the case. The photo below is from a slide on a talk about ebike systems that I gave at the VEVA meeting this past June:
On the left is the functional schematic for a non-regen controller, and on the right is the schematic for a regen controller. You can't see a difference because they are identical, the only thing that makes the regen controller do regen is the manner in which the MOSFETS are turned On and Off during PWM.
Few of the common ebike controllers operate in regen simply because the firmware or intelligence needs to be a lot more sophisticated. If you took a Crystalyte controller and changed the mosfet drives to do 2-quadrant PWM, then as soon as you let go of the throttle the motor would come to a dead regen stop. A simple throttle -> PWM doesn't work, the PWM output has to be based around sensing the current flow to and from the motor. If the battery gets disconnected on a controller while doing regen, then the regen current would all get dumped into the main controller capacitor which would overcharge and blow it up in an instant, so the firmware needs to be quick to detect and respond to these kinds of situations as well.
So far I've put nearly 40 amp-hours back into the pack from Regen, that's a full charge for free! It's true that as a percentage of energy used we're just at 2.5%, but that's because on long distance rides like this there isn't much stop and go activity. My experience with using regen in the city is that you typically get between 5 to 10% back, and the majority of that is from stopping rather than from hills. You can still argue that's not much, but you can't say it's not worth it when it comes for nothing.
Mike mentioned less brake wear as being a significant factor, and as someone who dislikes adjusting and replacing bicycle brake pads I couldn't agree more. But the single, biggest plus of having regen:
You all know how by far the most common first question everyone asks when they see your ebike is "Can it recharge while you pedal?"
After years of always having to give a nuanced answer about "only when you're fast enough that the back-emf of the motor exceeds pack voltage etc. etc.", I can finally just say "YES!"
-Justin
