Or do I need a special control circuit aside from the included electronics?
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I don't believe they do. What would be needed would be a sensor in the brake levers that measured brake force, and I believe that the most they have there is a cutoff switch. But there are a lot of different schemes.– Daniel R HicksOct 6, 2014 at 22:07
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1The big thing is that theres simply not that much power to be recovered on an electric bike. On the other hand, regenerative braking has been used in motorcycling racing (illegally).– BatmanOct 6, 2014 at 23:31
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@Batman there is a lot of power, just not much energy. 1kW is a lot of power in cycling terms, but it's easy to get that as available input to a regenerative braking system.– MóżOct 7, 2014 at 22:06
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2 Answers
For the most part, no.
The main problem is that you don't brake for very long compared to a normal battery charging cycle, so regenerative braking doesn't match the battery very well. Some systems use supercapacitors because they're designed for this sort of situation, but those are expensive and heavy in a bicycle application. Motors also typically don't work as well generating as motors, so they'll be less efficient, meaning a standard 250W motor might put out 200W as a generator.
The physics is pretty simple: a 100kg rider travelling at 36km/hr (10m/s) has E = 1/2 m v² = .5 x 100 x 10² = 5000 joules of energy. That's 5000 Watt-seconds. If you gently brake to a standstill in 5 seconds you're putting 1000W into your brakes, assuming no air resistance.
A typical battery is 36V and about 15AH, = 36 x 15 x 60 x 60 = 1,944,000 Joules or 2MJ, and takes 4-10 hours to charge. Pushing 5kJ into that isn't going to make a lot of difference - it's a 2000/5 = 4% recharge, assuming 100% efficiency. And you're not going to get 100%.
A much better scenario is either you pedal against the regenerative brakes, or you spend half an hour going down a long steep-ish hill, generating 200W all the way. Since a typical rider puts out 150-250 watts, for you to charge at that power level will mean pedalling very hard - you're going to need 300W or more to keep the bike moving, more like 500W taking into account all the losses. A world-class cyclist can put out 500W for an hour... and after that hour, the battery will be 30-50% charged.
This google search gave me a good explanation, a dismissal of the idea, some strongly held opinions and a couple of production bikes that have it.
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The physics is simple. If it is 1000W to go from 36 to 0 then it is 1000W to go from 0 to 36. 1/2 m v² = 1/2 m v². % recharge has nothing to do with this unless you are into an over charge. Why would I pedal against the regenerative brakes? Really you think a Prius owner would step on the accelerator an brake to increase mileage. Oct 6, 2014 at 23:45
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@Blam, it's 5000J of energy to go from 36 to 0 or 0 to 36. The only reason 1000W comes in is the assumption of braking in 5 seconds. If you could deliver 1kW you could theoretically accelerate from 0 to 36 in 5 seconds as well (ignoring losses, gear changes etc). You're right that there's no point pedalling against a regenerative system.– Chris HOct 7, 2014 at 10:25
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A recent question here was about using an ebike on a commute to the top of a serious hill. In that (rather niche) case regenerative braking might be of some use. If any supercaps replaced Li-ion batteries they would save weight - but even if they added weight, ebikes tend to have very heavy frames - an alloy frame instead of steel would soon deal with that.– Chris HOct 7, 2014 at 10:28
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2The "no point pedalling against regen" is only true because of the low efficiency, so it's a popular question to ask. Assuming 100% efficiency, it makes sense to put a little bit of power into the battery on the flat or a slight downhill while pedalling so you can use that power later to blast up the hills. It's not obviously silly until you actually know that system efficiency is a joke.– MóżOct 7, 2014 at 22:03
I have implemented a somewhat regenerative braking. To simply answer your question, you would need to read the manuals to see if they specifically mention regenerative-braking (RB). If RB is not mentioned, then your controller does not have RB implemented.
The regenerative braking (RB) I have made works independently from the bicycle brakes. These are the experience I have:
- Very useful in a hilly terrain, you would not need to worry about your acceleration cruising downhill, whilst charging your battery at the same time.
- Somewhat useful for commuting, but do not expect the RB to stop you effectively from 36 km/h speed. It would be dangerous to rely on RB as primary braking system for commuting.
All the calculations and designs I have made for this brake is fairly complex. But all of them pretty much branches from the basic idea, linking to this discussion here e.se.
However to give an analogy for all the cyclist here in SE, I would compare it with en Engine braking in car/automobiles. The lower the gear you set for the engine (I.e. higher spinning RPM of the Motor with respect to your Motor normal running speed), the more effective braking would be. There are two ways to achieve this:
Mechanically: Mid drive motor connected to the wheel with different gearing (for RB) and works independently with another gearing that would drive/accelerates your bicycle. This setup would have limited braking efficiency at different speed, depending on your RB gearing.
Electronically (easier to do):
- Brushless Hub motor + A step-up voltage regulator to maintain the voltage needed to charge your battery.If you use 36V, you would usually need 37-38V to charge back to the battery.
- A switch to change the mode between running the motor and RB.
The only reasons I think RB is not yet common for bicycle is the cost OR the complexity for a normal user to do as a DIY. When I first started my RB project, I was put off with the complete controller price, and decided to start designing a circuit of my own.
