Anyone ever tried to implement regenerative braking?

mr_ed

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Feb 15, 2022
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I did a lap of the Isle of Wight yesterday... 85 miles on my BBSHD from a 17.5Ah 52v battery.... so I was running at very low power levels typically about 100-150w and coasting down hills.

Its a heavy old beast and I was putting some effort in on the hills. There's a lot of hills and they're equally interspersed by downhills....

Got me thinking has anyone ever experimented with regenerative braking? Are there any products available to do so?

It'd also be really cool if you could fast charge an e-bike from a public electric car charger!
 

mr_ed

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Feb 15, 2022
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Hmmm I see a hub motor can be used to do regen, but most often they're not because they have a freewheel mechanism. I see some people are welding that solid, but then that will remove the ability to coast or vary the braking effort. I was hoping there was something more intelligent than that, perhaps connected to brake switches.
 

AGS

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Feb 12, 2023
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I find regenerative braking annoying because it activates and slows the motor down as soon as I come off the throttle so I can’t coast. I could set it up so it comes on at a slower wheel rpm, but it would then come on so late that it isn’t worth using.

I have activated ebraking instead to power assist my braking when I use the brake levers. I have just been playing around with the settings and raised my ebraking from 30 amps to 50 amps and I’m now quite happy with the way it performs.

Regenerative and ebraking will only work on direct drive motors.
 

mr_ed

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Feb 15, 2022
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This video was quite informative:

Seems you'll only get about 10% of the energy back that you put in... So not worth carrying any extra hardware around for. If you can do it using your existing motor then maybe... I was naively thinking it could be much higher.
 
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mr_ed

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Feb 15, 2022
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I find regenerative braking annoying because it activates and slows the motor down as soon as I come off the throttle so I can’t coast. I could set it up so it comes on at a slower wheel rpm, but it would then come on so late that it isn’t worth using.

I have activated ebraking instead to power assist my braking when I use the brake levers. I have just been playing around with the settings and raised my ebraking from 30 amps to 50 amps and I’m now quite happy with the way it performs.

Regenerative and ebraking will only work on direct drive motors.
Does your motor clutch in/out when you activate the regen then? I like the idea of a progressive lever (like a thumb throttle) to give variable braking.

I suppose it could be done with a mid-drive motor if there was no hub-freewheel, although not sure the chain would take forces in the other direction... maybe a belt drive....

I'll shelf the idea... but maybe something nice on ebikes in the future.
 

AGS

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Feb 12, 2023
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He is using a regen throttle for variable braking which is quite good. I don’t have the wiring for a regen throttle on my controller. And I don’t know if my firmware even supports it.

Mine is direct drive, so I don’t have a clutch.

You need good torque arms for regen and ebraking and need to check the motor nuts are tight regularly because the torque generated in the reverse direction can loosen the motor nuts. I have an additional lock nut on each side.
 

mr_ed

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Feb 15, 2022
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Thanks. Now I understand that some hub-drives are permanently engaged motors.

This video is quite good too:

Hopefully we'll see this stuff as standard and nicely developed in future.

I think this morning I naively assumed I could add a small dedicated regen front hub and regen 50%!
 

Benjahmin

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The physics just don't stack up for e bikes. With a car you're talking about something that is 1.5-2 tonnes or more. The stored kinetic energy is far far higher than a bike weighing around 100kg all up. Result is you need to carry more weight to achieve braking, thereby using more battery power to lug it around and climb hills. This offsets the very minimal gain in regen. Plus you'd need a direct drive motor, rather than a geared hub, more weight, less efficient and crap at climbing hills.
All in all better to spend money on a higher quality bigger battery.
 
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flecc

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Thanks. Now I understand that some hub-drives are permanently engaged motors.

Hopefully we'll see this stuff as standard and nicely developed in future.
No chance, it's been tried many time of bicycles and has never succeeded. BionX with their direct drive rear wheel motor had four drive modes rider selectable and equally four regeneration modes selectable, but the latter was just ever harder work for hardly any return.

Giant Bicycles, one of the largest in the industry, had a determined try using a Sanyo front hub motor that was originally designed with efficient regeneration expressly in mind. Reviewers were unanimous in saying the regen was scarcely detectable. The most experienced reviewer summed up the overall performance with this phrase, "one could die of boredom", not what anyone wants from an electric assist bicycle!

A bicycle even with rider weight simply doesn't have the mass and speeds to make regeneration worthwhile. My current model 1.3 ton Nissan Leaf e-car has selectable modes for regenerative braking, but selecting a higher mode doesn't give any return, the range from its 40 kWh battery remains the same. So even with an e-car's weight there's little if any gain from regenerative braking.
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AntonyC

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Apr 5, 2022
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Terrain probably counts for a lot, much of the time I'd manage with a spoon brake so there's nothing to recover, but descending long steep hills coasting drag uses nowhere near the energy available for regen. Regen's stress reversals used to mean it needed a direct drive (DD) hub motor, and for long hills those are large and high current, so it didn't suit our 250W builds as much as some US builds.

On the plus side Grin sell a regen-modified low-ratio geared motor < 3.5kg, and a regen-capable controller adds little weight. Cost aside that's not far off the sizing of a Woosh Gran Camino i.e. for the UK market. There's also the Chargebike system in the pipeline for achieving regen with geared hubs and free coasting. In a motor without permanent magnets (like Mahle, only in a hub) there needn't be cogging.

So viable (cost-wise) regen may yet come to smaller systems where the terrain's mad enough i.e. hills dominate the kWh in a ride. I don't think weight is the issue because weight, energy recovered and expended all scale the same way.
 

saneagle

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Oct 10, 2010
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Regen is a complete non- starter on an electric bicycle. If you try it, you'll see what I mean.

Fast charging shortens battery life - not recommended. It causes fires too!
 
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mr_ed

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Feb 15, 2022
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Regen is a complete non- starter on an electric bicycle. If you try it, you'll see what I mean.

Fast charging shortens battery life - not recommended. It causes fires too!
Can you explain why regen is a non-starter? I suspect its just been poorly implemented to-date with e-bikes. With the right controls and hardware it could work really well I think. Built into the motor so no extra parts required and with a proportional/variable brake lever control where the mechanical brakes only engage after full regen is reached.

I have to do a lot of braking on my e-bike... that braking could be done via regen with the benefit of getting some electrons back. The chap in the Grin video has obviously put a lot of effort into trialling it and developing the controls; he has some good ideas.

Similarly with fast-charging.... I don't think it has to shorten battery life or cause fires. It works ok for Tesla where they can recharge something like 50% in 20 minutes. If I could do that on my e-bike I could carry a much smaller battery and go on much longer leisure/touring rides without having to use hotels to charge overnight. Again, I think currently its a case of e-bike batteries & chargers not being designed for fast charging, but if the technology/margins/safety mechanisms were brought across from electric cars then it shouldn't have the problems you describe.
 
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saneagle

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Can you explain why regen is a non-starter? I suspect its just been poorly implemented to-date with e-bikes. With the right controls and hardware it could work really well I think. Built into the motor so no extra parts required and with a proportional/variable brake lever control where the mechanical brakes only engage after full regen is reached.

I have to do a lot of braking on my e-bike... that braking could be done via regen with the benefit of getting some electrons back. The chap in the Grin video has obviously put a lot of effort into trialling it and developing the controls; he has some good ideas.

Similarly with fast-charging.... I don't think it has to shorten battery life or cause fires. It works ok for Tesla where they can recharge something like 50% in 20 minutes. If I could do that on my e-bike I could carry a much smaller battery and go on much longer leisure/touring rides without having to use hotels to charge overnight. Again, I think currently its a case of e-bike batteries & chargers not being designed for fast charging, but if the technology/margins/safety mechanisms were brought across from electric cars then it shouldn't have the problems you describe.
Try it, then you'll see. Basically, you change a power assisted bicycle into a bicycle assisted power.

Why not take it a stage further, which some guys did, like put an extra hub-motor in the front wheel and use it as a generator to charge the battery while you power the bike with the other motor that discharges the battery. Your battery would last much longer like that.
 
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AGS

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Feb 12, 2023
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I think Justin is trying to push regenerative braking because he has designed the phase runner to operate with all of the functionality that he talked about in the seminar and wants people to buy it together with his all axle motor and cycle analyst.

It seems to work as he explained, so if you want it go to the Grin site and buy all of his products. But be aware they are premium prices.

 
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Ghost1951

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Jun 2, 2024
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Try it, then you'll see. Basically, you change a power assisted bicycle into a bicycle assisted power.

Why not take it a stage further, which some guys did, like put an extra hub-motor in the front wheel and use it as a generator to charge the battery while you power the bike with the other motor that discharges the battery. Your battery would last much longer like that.
One of the best things about a bicycle is the ability to freewheel for long distances without losing speed on the slightest inclines. Regenerative braking would sacrifice all that for a negligible input of energy put back into the battery. Problem is that the efficiency of the generation would be way less than the distance lost in free wheeling.

One of my sons bought an older electric car as a second car, which has quite strong regenerative braking whenever he backs off on the accelerator. I suspect that this only means he uses more battery power than he is getting back by having to hold open the accelerator to keep the damned thing going when it could have freewheeled. Fortunately, he can charge it free at work so if there is inefficiency in this, it does not matter.
 
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mr_ed

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Feb 15, 2022
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Try it, then you'll see. Basically, you change a power assisted bicycle into a bicycle assisted power.

Why not take it a stage further, which some guys did, like put an extra hub-motor in the front wheel and use it as a generator to charge the battery while you power the bike with the other motor that discharges the battery. Your battery would last much longer like that.
That's not a very helpful explanation! I'm not suggesting doing anything like you suggest.... I'm suggesting using the existing motor to implement regeneration only when you're braking... who knows maybe you could do away with the mechanical brakes altogether.
 

mr_ed

Pedelecer
Feb 15, 2022
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One of the best things about a bicycle is the ability to freewheel for long distances without losing speed on the slightest inclines. Regenerative braking would sacrifice all that for a negligible input of energy put back into the battery. Problem is that the efficiency of the generation would be way less than the distance lost in free wheeling.
I'm not suggesting the regenerative braking is active all the time.... only when you squeeze the brake lever and in proportion to how much you squeeze it...

The physics works... there is kinetic energy being wasted as heat/friction when we brake. We have the tools (motor/battery) to harvest it if we wish to.

I've concluded that for various reasons, noone has done it well on a bike so-far. I'm sure they will in future..
 

saneagle

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That's not a very helpful explanation! I'm not suggesting doing anything like you suggest.... I'm suggesting using the existing motor to implement regeneration only when you're braking... who knows maybe you could do away with the mechanical brakes altogether.
I've tried it on many bikes. It's useless. Maybe it gets you 2% more range for nothing, but it spoils the whole ride, so you wouldn't want to extend the ride anyway.

We don't get much mention of it these days because the manufacturers that tried it got burned. Most of the threads on this forum are from people asking how they can turn it off.

If you think it'll work for you, then try it. Personally, I think you'd get more and enjoy your bike more if you put duct tape around the spokes as vanes, then use it as a wind generator every time you park up for a rest, or just clip a solar panel to the sunny side of your bike.
 

flecc

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Oct 25, 2006
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Similarly with fast-charging.... I don't think it has to shorten battery life or cause fires. It works ok for Tesla where they can recharge something like 50% in 20 minutes.
Only at the cost of battery life and an appalling record of totally burnt out cars. Most of the worldwide story of e-car fires is a Tesla story. The launch of their model A was delayed four years, in part due to the fires, with at least three cars burnt out during that time.

Nissan know more than most about e-cars, their Leaf beat Tesla to market by two years with a family carrying car, and they say the biggest factor in shortening battery life is fast charging, the faster the charge, the shorter the battery life.
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