# Possibly dumb questions



## DCBassman (23 Jul 2018)

I'm not about to get an rebuke any time soon, but wanted to know how sophisticated the drive systems are.
Considering the price of the things, I'd be wanting the machine to be able to add charge when coasting/descending, and at the money-no-object level, maybe regenerative braking also.

As said, maybe dumb questions, but...


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## NickWi (23 Jul 2018)

Read this:- https://www.pandaebikes.com/regen-braking-ebikes-worth/


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## DCBassman (23 Jul 2018)

Ok, no regen, no problem. The (to me) simpler problem, recharge in long descent, would seem eminently feasible on a hub motor, maybe more problematic on crank motors.
By the time I need or can afford one, maybe these questions will be closer to solution.
Me being me, I'd DEFINITELY strap a solar cell on somehow. Just because!


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## Pale Rider (23 Jul 2018)

Recharging on a long descent is a non-starter.

It's true the motor, if being spun by the bicycle's wheels, would produce a tiny amount of current.

But that amount is truly tiny and can only be produced - at the expense of some drag - for the length of time the bicycle is going downhill, which is only a few seconds or a minute or so at a time.

Using the far pokier mains (rectified) charger takes hours to charge an ebike battery.

Using the mains charger for 10 minutes would make no noticeable difference to the state of charge of the battery, and that's way more charge than you could ever produce on the road.


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## DCBassman (23 Jul 2018)

A well-designed dc motor should be able to produce more than a tiny current when 'used in reverse'. If not, it's probably not a terribly efficient motor to start with. The key is good permanent magnets. If these motors have field coils, and would need excitation to generate, that's more of a problem.


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## Laser Man (28 Oct 2018)

Modern brushless motors are plenty efficient enough to put lots of current back into a battery (given the right circuitry).

There's a big snag though - in order to recharge the battery, the motor must take power out of the bike.
So regenerative is only a good idea if you want to fly up hills and crawl down them!


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