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I'd like to install a dynamo hub in a trike application where it will spin "backward" compared to how it would spin on a normal bicycle (I can't turn it around because I need the disc brake to face the right side).

Is there any difference at all in performance of dynamo hubs if they spin one direction versus the other?

BetterSense
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  • The problem would be if the "brushes" were designed for only direction. – Daniel R Hicks Jul 11 '22 at 16:48
  • @DanielRHicks I'm pretty certain there are no brushes in dynamo hubs. The part that rotates with the wheel has magnets, lots of them in alternating orientations to create high enough frequency that flicker doesn't annoy you. The part that is stationary with the axle contains the induction coils that create the electricity from the rotating magnetic field. – juhist Jul 11 '22 at 16:54
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    the electronics all work but most hubs unscrew, see above very similar question. there are a few hubs now that don't seem to use a screw-together shell design, so one could ask the follow up question of whether those particular hubs have the same problem. – Nathan Knutson Jul 11 '22 at 16:55
  • Completely unrelated - do feel free to share progress pictures of your build. It sounds fascinating - [chat] might be the best place for that. – Criggie Jul 11 '22 at 22:21
  • SON does make dyno hubs specifically for trikes. – Adam Rice Jul 11 '22 at 22:50
  • When you're asking about "performance", are you asking about physical or electrical performance? – End Anti-Semitic Hate Jul 12 '22 at 01:33
  • @juhist re: flicker - it's fine with halogen lamps even at low speed, but LEDs can strobe fast enough that they visibly flicker without filter electronics (in the light, not the hub). I have a cheap front light with no filtering and it's quite annoying. It also lacks a standlight feature - the capacitor for that can provide sufficient filtering – Chris H Jul 12 '22 at 11:14
  • @DanielRHicks, juhist is right - bike dynamos aren't really dynamos, they're alternators – Chris H Jul 12 '22 at 11:15
  • @ChrisH - Yeah, I've never taken apart a bike dynamo, but, generally speaking, many alternators have brushes to supply current to the rotor. – Daniel R Hicks Jul 12 '22 at 11:56
  • @DanielRHicks slip rings are more common than brushes as the rotor coil doesn't need to be commutated. But in modern bike generators, permanent magnet designs are used - no field coils at all – Chris H Jul 12 '22 at 13:34

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Dynamo hubs create alternating current. And fairly peculiar alternating current at that: although they are nominally are 6 volts, you can easily get several tens of volts by riding fast and connecting a high resistance load (or no load at all). They are intended to be used with 12 ohm load, in which case they output 6 volts and 0.5 amps at normal riding speeds and any speed higher than that.

If you reverse the rotation direction, it will reverse the flow of current. But since it's alternating current, it doesn't affect you in any way at all. It's equal to disconnecting a device connected to 230V mains socket, reversing the plug and connecting again. In many countries, the 230V mains plugs connect either way and work equally well either way.

Edit: as Nathan Knutson found out, some dynamo hubs still could self-unscrew if rotating in the incorrect direction. So you probably want to check Consequences of driving a dynamo backwards -- electrically, they work but mechanically it depends on the hub model.

juhist
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