What if we had 200W bicycle dynamos ?

[Martin]

If you had 200W of electric power available on your bicycle, would you have a use for it ?
If available downhill only ?

Me just thinking: Popularity of electric bicycles has produced a wide range of hub-motors that are meanwhile easily available and inexpensive. These days most of them are brushless. Such brushless motors have rare-earth magnets on the rotor and copper windings on the stator. The nicer ones have enough poles to go without a transmission / planetary gear. All of this is integrated into a front- or rear bicycle hub. Example.
What would keep me from rectifying and combining all windings of such a motor to extract power as if it was a dynamo ? It's built like a dynamo, some electric bikes actually use it as a dynamo (recuperative braking), so why not buy one in order to use it exclusively as a dynamo ?

Anyone done it before, what's the experience ?

What electric power could a bicycle hub motor generate when it's rated 250W / 500W / 750W (driving power) ?
(assuming the athlete's muscle power is not saturating)

 

[John_Galt]

It's probably designed so that it only acts as a motor, not a generator. Assuming it could provide 200+ watts (downhill) I'd be looking towards something along the lines of 30,000 lumens + of pure, unfettered, XP-G, MC-E, XP-E goodness!


Who says we can't have enough light now? Anyone? With 30,000 lumens?

 

[R@ndom]

Surefire way to blind yourself. Even cars only have 7000 lumen in dual 35watt hid setups. Then again this forum is all about excess.

 

[znomit]

Heated handlebars?

 

[kananga]

IIRC they're still "commutated", but with the controller. Hrm... They should still kick out some AC when they're turned, but what's going to come out of that motor, volt and ampwise? Now I'm curious! Googling...

 

[Szemhazai]

Martin, get down to earth... You probably won't be able to generate such power for more than 1/2 an hour

 

[Martin]

I've contacted the Chinese dealer (or maker ?) of the above-linked motor and they insist that it's a motor not to be used as a dynamo. I don't believe it. From what I understand, the higher-power versions are designed for a higher voltage (more windings), not more current.

to kananga: I'm told that all the electronics are in the controller, so the hub doesn't do any commutating by itself - just like a dynamo.

At the Eurobike show, I've been spinning some of the hub motors by hand and they feel like big dynamos. I just wonder if the current and voltage delivered is similar or somehow related to the intake in motor mode. Couldn't find any info on this on the Internet, looks like it needs an experiment.

to Szemhazai: Has nothing to do with stamina. Merely a matter of the altitude you start at..

 

[znomit]

Martin I've always wondered about the usefulness of a handicap device for roadies.
So on your usual bunch training ride instead of hanging off the front you dial up 40W and struggle to keep with the pack. And of course you have warm hands

 

[Martin]

My own use for such a solution would not be brighter headlights but power generation on a stationary bike. I get such requests from time to time, mostly from students who want to do some school project. A popular solution is to somehow run a DC motor on a bike's rear tire, but with current motor hubs it could be so much more convenient and efficient - just replace the rear wheel and put the bike on a stand.

Recently I was in a situation where I put my own bike on a stand and had someone pedal for light (my bottle dynamo runs on the rear wheel), so someone else could cook me a meal. While I waited for my meal, we elaborated on the idea: 100 to 200 W of electric power could illuminate all huts in this village and charge all cell phones and headlamp batteries at the same time. One person would pedal from 7pm to 9pm and another person from 9pm to 11pm. With 50 people in the village, every one has to pedal for 2 hours every 20 days. Those villagers present considered that very acceptable as it frees them from buying gas and messing with an unreliable old genset every night. So when the lights go out, no need to get oily fingers on the genset, just shout the name of the person who's supposed to be pedaling..

 

[Szemhazai]

Martin, you are not the first one...

http://scienceshareware.com/bicycle-generator-faq.htm

 

[Linger]

I vote for the insanity.

I saw these and wondered about putting one on the front wheel of my bicycle. Now this isn't an electrical motor converted to generate electricity, this is ...never mind, I cut/paste what it is. (i have no connection with any of this, just saw it while browsing for diy electricity)
////////////////////

Got Watts?

The stator, in conjunction with the flywheel, drives electrical output for the motorcycle or ATV. The stator is located in the engine side case on the left side of the motor (on most off-road machines). As the magnetic flywheel spins around the stationary stator, electrical current is created in the copper wire.


http://trailtech.net/stators_and_electrical_system_kits.html

1. Stator kits contain stator only. See electrical system kits for kits that also contain regulator/rectifiers and model-specific connectors.
2. Regulator/rectifier and battery sold separately.
3. Designed for use with Trail Tech regulator/rectifiers.
4. Trail Tech stators replace the OEM stator.
5. Trail Tech stators increase power output significantly.
6. Trail Tech stators will not function in a DC system without a Trail Tech regulator/rectifier.
7. AC systems may use a Trail Tech or OEM regulator/rectifier along with a Trail Tech stator.
8. DC systems will not function without a battery or capacitor in the system.
9. CRF's achieve 90 watts of DC power when installed with a Trail Tech high-strength flywheel.
10. YFZ450 achieves 100 watts of DC power.
11. Eliminate the dimming effect often experienced when an AC powered machine is idling or shifting between gears.

 

[jtr1962]

Just a couple of points here:

1) If you're looking to end up with 200 watts of power distributed in a village or elsewhere then you'll probably need to generate ~300 watts at the bike.
(the generator is at best about 80% efficient and the inverter needed to convert whatever the generator puts out to 120VAC or 240 VAC for distribution probably will be about the same). You NEED some type of usual household voltage, not DC, if you intend to use the power to do things like charge cell phones or run computers. If you're just going to use it for light or charging batteries, then you can probably get by with DC and avoid the inverter losses.

2) A generator which can put out either 120 VAC or 240 VAC at the proper voltage and frequency when pedaling at a certain RPM would be best as you eliminate inverter losses but it requires a very steady cadence AND I'm not even sure such a generator exists.

3) A small battery in conjunction with the generator is probably a good idea so that the power doesn't go out when pedaler's are switched.

4) Given that you need a very well conditioned person to maintain the 300 watts mentioned in 1) for 2 hours, it might be better instead to split the generating duty among 2 or even 3 persons. 150 watts for 2 hours is doable for most people in reasonable shape. 100 watts is something even a lot of kids can manage (i.e. the potential pool of pedalers increases). Also, maybe one generator can be AC for things not amenable to DC, while the other one or two can be DC.

5) Solar panels and batteries might be a better idea long term even though they cost more.

 

[kananga]

http://trailtech.net/stators_and_electrical_system_kits.html

Hey, that looks familiar! Just like the inside of a brushless DC motor.

I didn't look too hard, but managed to google up a few mentions of brushless dc bicycle hub motors on diy wind power discussion board posts. No details, just a few quick mentions of how awesome they were at generating electricity. Kind of a "come to the dark side" sense to it. It's tough to dig for info on repurposing these motors with all of the startup importers flooding the search results any time you search for "bicycle" and "hub motor". About 3/4 of the worthless results disappeared with a "-china" in the search terms, but there's still a lot of junk to wade through.

Regardless, bldc motors are spoken of lovingly when actually repurposed as generators by people who've done this kind of thing before! I just wish they'd post something useful...

 

[syc]

I have a Crystalyte hub motor that has been waiting around as a DIY electric bike project for a while. The motor hubs can definitely be used for regenerative braking if the controller supports it, here's a link on an electric vehicle forum that has some links.

You can also ask around that V is for Voltage forum, there are some serious electric bike hackers there - though I don't recall many of them digging into the controller electronics.

My own use for such a solution would not be brighter headlights but power generation on a stationary bike. I get such requests from time to time, mostly from students who want to do some school project. A popular solution is to somehow run a DC motor on a bike's rear tire, but with current motor hubs it could be so much more convenient and efficient - just replace the rear wheel and put the bike on a stand.

Recently I was in a situation where I put my own bike on a stand and had someone pedal for light (my bottle dynamo runs on the rear wheel), so someone else could cook me a meal. While I waited for my meal, we elaborated on the idea: 100 to 200 W of electric power could illuminate all huts in this village and charge all cell phones and headlamp batteries at the same time. One person would pedal from 7pm to 9pm and another person from 9pm to 11pm. With 50 people in the village, every one has to pedal for 2 hours every 20 days. Those villagers present considered that very acceptable as it frees them from buying gas and messing with an unreliable old genset every night. So when the lights go out, no need to get oily fingers on the genset, just shout the name of the person who's supposed to be pedaling..

 

[fyrstormer]

If you had 200W of electric power available on your bicycle, would you have a use for it ?

If we had 200W bicycle dynamos, nobody who had them would be able to move. Even the best bikers on the planet can't sustain more than 500W for more than a few minutes. It would never work for a normal person. Better to use batteries and LEDs instead of anything that powerful.

What would be really nice is a dynamo hub that uses regenerative braking to charge a battery pack that runs the lights, because it would at least capture energy you would otherwise waste.

 

[Martin]

Great resource that you linked, Szemhazai !

This week my motor arrived and I set it up:

This motor uses no gears, makes it real big and heavy. Constructed like a dynamo, just this one is 3-phase.

It's a very efficient mechanical arrangement with no rollers, no belts.

I'm yet waiting for my rectifier diodes to arrive, so I can make a 3-phase rectifier. Couldn't resist playing with the thing as it is now:
Having fried some automotive bulbs, I figured it could be fun to try a fluorescent tube. Using a transformer, I managed to power 2 large (65W) tubes. They ignite somewhere between 500..700 V, after that the voltage drops to 200 .. 260 V.
One tube is more than enough for a child.
Now the nasty thing with fluorescent tubes is that they need a high voltage to ignite, then suddenly start drawing a lot of current. This creates a funny pedaling experience (video). At the end, the boy just can't ignite the tube any more.

Once I have the rectifier and charge a battery, the pedaling will be a lot nicer.

 

[Martin]

Rectifier arrived and set it up with a battery just as jtr1962 suggested:

Pedaling is very smooth now and I'm happy with the setup. However, jtr1962 is right: 200W of output for 2h on a stationary bike are unrealistic. Let me correct that to 50W (effortless) .. 120W (tough).
I also noted that an almost fully-charged battery needs a slightly different gear ratio than a depleted battery.

 

[sudarshan367]

dude martin!!
can you please help me with the dynamo arrangement on your bicycle. what's that big,black,round thing you put up on ur bicycle...please explain me the arrangement dude.

 

[jh333233]

Off-topic notes
when you pedal it, a repulsive force will be generated by the induced current in the generator
You will either need a large force or you wont be able to give 200W of power
"Conservation of energy, electricity must come from kinetic energy of bike, which means the one comes from ur body"

 

[Savvas]

Martin,
Isn't it the case that a hub generator's capacity if limited by it's 'flux' impedance (or whatever he correct terminology is)? In other words, the current generated reaches a certain point (in dedicated bike 'dynamo' hubs this seems to be around 500mw) and then the coils saturate and the output levels out. This very well known phenomenon is an inherent (and very useful) characteristic of all modern hub dynamos. Will it not apply to the arrangement you've put together? Or is your motor structurally and electrically different?
Savvas.