Hub dynamo - not connected

[simonineaston]

Does anyone know if there is any down-side to building a hub dynamo into a wheel and then using it without any electrical items connected ie without any current draw? I'm aware obs that there will be the usual wear to the bearings, but I was just wondering if not using it electrically had any risk, other than needless exposure to elements.
Bear in mind that I go around turning all un-occupied power points in my house to off so the 'leccy doesn't leak out... And I'm not really thinking about drag either - I get that a dyno-hub, even unloaded, will not spin as freely as a plain, non-electrical hub.

[Mick F]

Not really sure what you mean.

When any connected lights are switched off, the dynamo isn't connected to anything. Zero current draw.
This is completely normal, and my bike is like that for 99% of my riding.

[sukuinage]

It will have greater rolling resistance than a normal hub - you'd have to look up the actual figures but I think around 1 - 5 W depending on hub and speed. My commuter probably is in this mode for 95% of the time - connected but not powering the light, effectively no difference from open circuit.

[simonineaston]

I'm not surprsied you don't get what I mean Mick - I'm not sure I do !! I think I'm worrying needlessly - forget I asked...

[Mick F]

I think it's a valid question.
My lights are set to "senso" majority of the time, so it's quite possible that there is a tiny current draw by the electronics in the front light. I don't know - or care.

My front light has a three position slider. On, Off, and S.
There's nothing to stop me putting it to Off and leaving it there until I want the lights on, and then move it to the On position. The S position is a luxury.

[Nigel]

As in the posting from Sukuinage above. There's a bit of drag, not a lot, and the amount will vary depending on hub in question.

I've run a Shimano hub for many years, and might be able to just-about feel a tiny bit of drag above 20kph with no load (but this isn't a blind test, so it might be in my head). The lights attached (B&M LED front and rear) have an on/off switch on the front lamp, so off is "off", with nothing connected.
Other hubs will have different drag both on-load and no-load - I bought the Shimano as a price-performance compromise when compared to the then best SON hubs.

- Nigel

[Mick F]

Mines on a small wheeled bike - Moulton - so the drag will be more than on a "normal" bike.
How much more, I don't know. Can't say I really care.

I'd have to build up a spare front wheel with a normal hub and do a roll-out test for each to see if the drag makes any difference.
Done it with the lights off and then on, and when on it's a noticeable difference in distance run.

[Jdsk]

There are some drag figures (and lots more) in the review by Chris Juden and colleagues:

https://www.cyclinguk.org/sites/default ... ynamos.pdf

(I'm always amused by expressing drag as gradient... lovely craft metrology.)

Jonathan

[mattheus]

Does anyone ever read past the 1st sentence of a post anymore???

And I'm not really thinking about drag either - I get that a dyno-hub, even unloaded, will not spin as freely as a plain, non-electrical hub.

[KTHSullivan]

The hub will induce circulating current off load. On large industrial and marine applications its problematical as the power will induce "eddy" currents and subsequent heat in a naturally excited field coil.

The generator will also produce resonant noise by virtue of the production of a circulating current that would manifest itself as electromagnetic waves. From personnel experience these "waves" can sometimes interfere with the operation of wireless cycle computers.

Due to the low power provided by a hub dynamo and the disproportionate size of it's associated heat sink namely the dynamo itself I doubt very much if any problems would arise other than that stated above.

K

[simonineaston]

Does anyone ever read past the 1st sentence of a post anymore???

Gotta stick my hand up here, Mattheus - and admit that I added the remark about drag after I submitted the first post, so not the readers' fault...

[Jdsk]

Does anyone ever read past the 1st sentence of a post anymore???

Gotta stick my hand up here, Mattheus - and admit that I added the remark about drag after I submitted the first post, so not the readers' fault...

And we had read every sentence!

: - )

Jonathan

[mattheus]

Does anyone ever read past the 1st sentence of a post anymore???

Gotta stick my hand up here, Mattheus - and admit that I added the remark about drag after I submitted the first post, so not the readers' fault...

Aha!

Well, I understood you even without reading the addendum. I guess those members with lesser intellects had good intentions, so I shan't be too hard on them ...

[simonineaston]

I doubt very much if any problems would arise other than that stated above.

Excellent news - thanks !

[[XAP]Bob]

There are some drag figures (and lots more) in the review by Chris Juden and colleagues:

https://www.cyclinguk.org/sites/default ... ynamos.pdf

(I'm always amused by expressing drag as gradient... lovely craft metrology.)

Jonathan

It's a brilliant metric, because it actually means something to most people.