What power can a typical hub motor generate as a generator?

[rosjen]

Seems to me that a hub motor could generate a decent amount of power if used on a small wind turbine? On the subject of power generation, why is there a downer for regeneration on ebikes - what are the actual numbers and facts?

 

[flecc]

Seems to me that a hub motor could generate a decent amount of power if used on a small wind turbine? On the subject of power generation, why is there a downer for regeneration on ebikes - what are the actual numbers and facts?

I doubt if the output would be particularly good compared with a generator design. In motor form they are designed for economy of course. Working in reverse mode as a generator we need the opposite of course, the profligate output that a dedicated generator design gives.

As for e-bike regeneration, it's simply the lack of mass of a rider and e-bike coupled with the low bicycle speeds that make it unproductive. Earlier attempts with geared hub motors by the Birkestrand Corporation with their "magic wheel", Sanyo with their hub motor and and the Chinese with some of their cheaper e-bikes have all failed and disappeared. Only BionX with their direct drive motor retain it, but even there it only exists in an optional switched mode which few owners bother to use.

Panasonic have 3000 bikes on long term trial in Japan with front hub motors which are braking regenerators. They claim a massive increase in range of about 50% which is pure nonsense. No cyclist with any sense would do that much braking, since it implies a huge effort to put in both that much surplus energy in the first place plus the extra required to account for energy conversion effciency loss. The best cyclists avoid braking as much as possible of course to conserve their energy or to utilise downhill speed gain as kinetic energy directly wherever possible.

It's sobering to consider that the Formula 1 world has struggled to make their KERS braking generation energy recovery system work. There we have half ton cars losing most of 200 mph in as little as three seconds!!! If that massive potential can't easily pay off, what hope is there for a one-tenth ton rider and bike losing only 10 mph in a few seconds?
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[CeeGee]

KERS works perfectly well in F1 if the chassis is built around it. McLaren proved that point last season. The problem was adding it to an existing chassis and set-up. In an F1 car weight distribution is as important as aerodynamics and engine power in creating a fast package and the weight of the KERS hardware means you have a lot less ballast to move around to get a good balance for different tracks. This basically means that once you have it you are stuck with it and can't really remove it for slow twisty tracks.
The good bike rider uses their brakes as little as possible (have you seen the cost of brake blocks or pads), and the extra weight and cost for any very slight improvement in range is a non-starter unless somebody can find a much better system.

Colin

 

[flecc]

KERS works perfectly well in F1 if the chassis is built around it. McLaren proved that point last season. The problem was adding it to an existing chassis and set-up. In an F1 car weight distribution is as important as aerodynamics and engine power in creating a fast package and the weight of the KERS hardware means you have a lot less ballast to move around to get a good balance for different tracks. This basically means that once you have it you are stuck with it and can't really remove it for slow twisty tracks.

While I agree with this (apart from the "perfectly well") Colin, the potential of that huge amount of energy wasn't anywhere near realised, since if it had been the amount of gain would have far exceeded any handling disadvantage. The energy lost from losing 150 mph in 3 seconds is the same as that need to accelerate the same amount in the same time. With anything like that extra acceleration over their norm, the KERS cars would have annihilated the non-KERS opposition. Like all energy recovery systems the return is disappointing.

The good bike rider uses their brakes as little as possible (have you seen the cost of brake blocks or pads), and the extra weight and cost for any very slight improvement in range is a non-starter unless somebody can find a much better system.

The weight and cost gain is minimal though, it's the extra drag in geared motors that's the main problem, since the motor needs to be engaged all the time on a true regeneration system, greatly reducing the kinetic gain on downhills and making unpowered pedaling miserable. It's the customer complaints about that drag which prompted Giant to drop regen on their latest models which are now much nicer to ride.
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[CeeGee]

While I agree with this (apart from the "perfectly well") Colin, the potential of that huge amount of energy wasn't anywhere near realised, since if it had been the amount of gain would have far exceeded any handling disadvantage. The energy lost from losing 150 mph in 3 seconds is the same as that need to accelerate the same amount in the same time. With anything like that extra acceleration over their norm, the KERS cars would have annihilated the non-KERS opposition. Like all energy recovery systems the return is disappointing.

You are correct that it doesn't recover anywhere near 100%, but FIA regulations decreed that you could only use the KERS energy for 7 seconds per lap: that was to prevent the KERS cars annihilating the non-KERS opposition. The KERS system is capable of a lot more than that seven seconds, and I don't think we have seen the last of it in F1. If it can be properly planned and costed so that all the teams can afford it if they want it, KERS will return to Formula 1 unless FOTA decide they would prefer to bring back Turbos and persuade the FIA to agree.
Of course, don't forget we are talking about F1, FIA and FOTA here, so common sense and logic about development and regulations go straight out of the window.

Colin

 

[flecc]

Yes, your last comment caused me to smile at it's truth! F1 lost it's way decades ago.

As you say, I'm also sure F1 will try to use KERS on the basis that any gain is a gain, and the gain will certainly be greater than some of the more miniscule gains they make in aerodynamics.
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[Madness]

How strange, i was thinking about this today.

I have a converted bike which i use as a e-bike for work and on weekends i simple remove the battery and use it as a normal bike.

Im going on longer and longer rides on the weekends and thinking about using my iphone/gps for routing. This as it stands wont work as without something to keep the charge up it would die within 3 hours.

I pondered about using the power made from the hug to charge the iphone.

Do you think you could get enough for that?

 

[flecc]

It would easily produce enough for that, but if it's the usual internally geared hub motor it probably has an internal freewheel, meaning the motor doesn't turn when the power isn't used.

Tell us what motor/kit/e-bike it is and we will probably be able to tell if that's the case.
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[Madness]

Its makeing power for sure.

At weekends i ride without batterys and the lights come on on the thumb throttle so it must be coming from the wheel.

Its just a ebay kit that i have fitted.

Ill get a multimeter on it once i have it back on the road, went to go out today for a ride and had a clunk come from the back. Rear wheel is buckled (im guessing a spoke went).

 

[flecc]

That's not an internally geared motor then Madness, it's a direct drive one which is on all the time, though with hardly any drag normally from that type.

It will always generate but the output will be low, though I'd think plenty for your purposes.
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[Madness]

Thanks flecc for confirming this.

My plan is to put a small battery about 2Ah for storage and then run devices (im thinking might be able to run lights as well) form this, ill have to make something to step down the voltage but that shouldn't be to hard.

The bikes going into the shop Friday to have a new stronger rear wheel fitted as its broken 3 spokes now (about £35 for the wheel). Those led acid batterys are not light

When i got the moneys i think ill treat myself to a ping battery if my current plans of building a battery falls flat.

 

[Roderick Read]

I'm going to offer a ... well. .. unique perspective on this.
Short answer YES. An e-bike can be used as a flying wind turbine.