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What kind of circuit would be required to implement a regenerative braking system on a electrical assisted bicycle with a motor like this? enter image description here

The motor is brushless and the kit comes with a big ESC box. Regenerative braking was not an advertised feature.

As far as 'why do this': you could use it with a small battery for using energy (on the next hill) that would otherwise be waisted in burning up your brakes during long down hill stretches

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  • \$\begingroup\$ The linked question does not answer this question which can stand on its own regarding regen on a bicycle hub motor as there is a special mechanical consideration that prevents regen. See my answer below. \$\endgroup\$ – Transistor Jun 28 '16 at 16:22
  • \$\begingroup\$ i second that. plus the other answer was regarding a DC motor. Brushless motors are AC \$\endgroup\$ – Daniel Caoili Jun 28 '16 at 17:52
  • \$\begingroup\$ Regen braking on a bike is useless due to the fact that going downhill fast is FUN. Going down a 6% slope at 50 km/h means about 1kW of power is available. Usually it is wasted against wind resistance (ie, having fun going fast) but if the motor could harness it without overheating, then the battery would have to be able to gobble up this power to charge, and it can't. Ebike battery chemistry is optimized for energy per weight, and these chemistries do not like fast/high current charging at all. Wait until we have graphene super-battery-caps, then, it will work. \$\endgroup\$ – peufeu Jun 12 '17 at 21:15
  • \$\begingroup\$ Plus, braking hard on a traffic light will burn several kW heating your rims. No motor can do this without weighing too much, especially in the rear wheel, it would just lock the rear wheel and you'd crash. So the best approach would be to ride at the proper speed and time the traffic lights just right. \$\endgroup\$ – peufeu Jun 12 '17 at 21:21
  • \$\begingroup\$ @peufeu riding "at the proper speed" down a hill requires ongoing moderate braking; that rather than abrupt stops is actually the perfect place to salvage energy when the battery can accept it, and the rate of energy produced is likely on the same order as that at which energy is consumed when operating at top speed. As for the claim that it is not practical, the electric unicycle wheels have braking through the hub motor as their only real sustained braking mechanism, though they should be engineered to go into some kind of safety warning and eventual shutdown if the pack is full. \$\endgroup\$ – Chris Stratton Jun 12 '17 at 21:52
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You can not do regenerative braking with that wheel - but not for electronic reasons. The problem is mechanical.

That wheel will have a freewheel mechanism in it - otherwise it wouldn't rotate freely when pedaling without power. As soon as you apply any braking torque or if the bike runs faster than the motor the wheel will freewheel.

enter image description here

Figure 1. Example of a freewheel mechanism.

To confirm this with your wheel you should be able to freely spin the axle in one direction but not in the other.

I am an eBike user. I reckon I spend < 15 s braking on my 20 minute rural commute. The complexity of regen braking isn't worth it.

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  • \$\begingroup\$ I ride through a city. there's lots of ups and downs and busy cross sections. I brake quite a bit. \$\endgroup\$ – Daniel Caoili Jun 28 '16 at 15:02
  • \$\begingroup\$ are you sure that that one has a freewheel considering it's a front wheel. \$\endgroup\$ – Daniel Caoili Jun 28 '16 at 15:07
  • \$\begingroup\$ i got it! I could i do a bmx style handle bar flip and then regen brake. But really, in general, can switching two wires from an esc to a brushless motor (without a freewheel) produce reverse torque and cause the battery to get a little charge? \$\endgroup\$ – Daniel Caoili Jun 28 '16 at 15:11
  • \$\begingroup\$ @Jim: Please undo your edit to my post. You have reversed what I stated and put words in my mouth - "My experience ..., I paid $150, etc." (I'm in Europe.) Please post it as your own answer. Note that the wheel in the question appears to be a front wheel. I had a similar unit on a Powabyke and dismantled it for service and subsequently replaced it. It did have a freewheel which started clicking at 17 mph. I now have a Kalkhoff with Panasonic mid-drive which drives the chain. In any case, editing someone's post should be to fix typos and formatting problems not a change of answer. Thanks. \$\endgroup\$ – Transistor Jun 12 '17 at 22:34

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