Generate Power As You Ride With A Bicycle Planar Alternator

For most riders, bicycle lighting consists of an array of LED lamps and flashing gizmos, usually powered by lithium-ion batteries, or coin cells for the smaller ones. Some people though prefer to dispense with batteries and generate their own power, and that’s what [Thomas D] has done by fitting his bike with an alternator. But this is no off the shelf unit that rubs the tire or sits in a wheel hub. Instead, he’s built his own planar alternator that attaches to the spokes.

The design is inspired by those used in some wind generators, a central disk holding a set of planar coils sits between two rotating disks holding magnets. The stator holding the coils is made from laser-cut acrylic, and the rotors holding the magnets are sheet steel. One rotor is attached to the rear wheel spokes of the bicycle in close proximity to the stator which is attached to the rear frame. The second rotor sits on the other side of the stator while attached to the first rotor by its edge.

The coils are wired as two parallel groups in series in a ring with a single-phase output that feeds a rectifier and DC to DC converter. It would be interesting to see the effect of the same alternator with different winding arrangements or multiple phases.

This is the first time we’ve seen one of these on a bicycle, but this type of alternator has appeared here in more than one wind generator.

20 thoughts on “Generate Power As You Ride With A Bicycle Planar Alternator

    1. Doesnt mean you cant do it better or different. This is considerably better than the ol ‘friction drive tire eater’ that sadly still exists. Pump the pedals like a demon for maybe 6Watts. That lasted a whole week before I decided a couple SLA and wall charger were a far better option. Other rechargeable beta cells werent on a paperboys/delivery budget. Then again this was a time when LED tech was outrageous and a few candlepower cost way too much. Halogen bulbs were a reasonable solution then.
      In the configuration shown would be advantageous to use as generative braking but effort for producing power in addition to thrust would significantly change with gear ratio. Same issue as ol tire killer without the destruction and can add a kill switch on handlebars. Turning around and flipping the tire killers mechanical engage was also an issue. Assumption being that it didnt come out of alignment as well. Wet tire wouldnt help either.
      Be nice to see what you come up with.

    2. Every original idea was thought up half an hour after the creation of the first man, everything else is just an incremental improvement or a variation on a theme, so go for it.

    1. i had this amazing light…it really had a beam pattern like a car head lamp. i thought its only downside was all the extra effort on the uphills, but then one day i found out, it had worn clean through my tire!!

      1. Maybe. I’ve seen plenty of bike tire sidewalls rot out before the tread. UV damage. The natural beige “whitewall” ones are the worst for it, guess at least the carbon granules in the black rubber limit the penetration depth.

  1. Presumably, this could also be used in reverse as a motor?

    I wonder what the big deal is about winding rectangular coils? All you need is a rectangle to wind them around!

  2. Careful! I just fried one one of those 6 LED Horror Fright lights which should have worked with a bottle generator diode bridge and capacitor setup. It didn’t light up and I still had the switch from the light in the path. I didn’t know which state the switch was in and cranked up the unloaded voltage then switched it on. No light and I knew something was not working. Testing the light on a bench supply confirmed my mistake. Back to the free 20 little diodes light with it’s low efficiency LED’s. I will try again. Note this setup does not have any regulation of current because the generator is current limited by itself. It is less than the LED max current. Full light at walking speed and nothing more at any faster speed.
    Gumwalls suck. Something for slightly lower resistance riding and faster rot.

  3. Hmm good to see a worthwhile approach though raises the question of interactions between the coils and magnets given what appears to be parallel current flow positioning ie Could power be robbed due to torque ripple and magnetising current at differing speeds as the power generated can drive other coils depending on phase matching ?

    I’m curious if:-
    1. Any torque ripple tests have been done across the range of speeds it’s intended to operate ?
    therefore leading to:-
    2. Watt is the efficiency at various speeds for actual power spread delivered ie which points to 1 in terms of optimising magnet to coil orientation and winding series/parallel permutations reducing robbing ?
    3. Adding suitable ferromagnetic material to coil cores could assist efficiency whilst minimising torque ripple ?

    In general, imho the idea is worth pursuing more so with an optimisation procedure. I’d like to see a battery added with a option/means to turn off charging when driving the pedals with any reasonable torque, unless battery must be charged or optional over ride. That way it doesn’t impede hill climbing, well unless you want the extra exercise, whilst charging battery more when slowing down eg matching a SMPS to maximise charge current to assist braking such as within battery capacity to take higher charge current now and then etc
    Thanks for post, cheers

  4. Front hub dynamos are on the market since at least a decade. ~5 W of drag for 3 W of electric power. Very common on trekking bikes. In my opinion, although experience is gained (and shared!), there is no need to reinvent the wheel (literally).

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