Bicycle Mechanics - Generator light strangess

I have a Lumotec Oval sensor headlight wired to a Shimano generator hub (the newer version, I forget the model number). This setup has been working great for about a year, but this past weekend I swapped out my fork and now I'm having problems.

The light still works fine in "Auto" mode (where it's switched on and off by the built-in light sensor). But when I flip the switch to On, it sometimes works and sometimes doesn't. Fortunately I use Auto most of the time, but sometimes when it's rainy I want the headlight on even if it's not dark enough to trip the sensor.

Most generator light problems seem to be wiring or grounding issues, but I can't figure out why the Auto mode would avoid that -- or why the problem is intermittent.

Both the old and new forks are steel, and the light is mounted to the fork crown. The bracket is metal, which apparently causes grounding problems for some people with the Shimano hub, but I've never had an issue. The bracket is also painted, so I'm not sure if it's making an electrical contact or not.

Any ideas?

dirty switch?

What Demon said. I would make sure the switch contacts are clean then start tracking the ciruit down with a multimeter.

Aaron:)

You'll probably have to ditch the light, I think, or persist with the switch in one position only, or send it back to the guy you bought it from and ask for a warranty claim (good luck on that one!!!).

I had a Senso Plus like yours and was extremely happy with it for a year or more of commuting and randonnees... then the slider switch went on it. And the switch is almost unserviceable without busting the plastic bits and pieces, which leaves you with no light. The same applies to the ordinary flick-switched Ovalplus, which also went cactus.

I am afraid these issues are what eventually turned me away from the Ovalplus to the E6, which has a magnetic reed switch and the electronics are pretty well sealed. The ingress of water is obviously a design flaw for the Ovalplus... as the North American importer even admits, there are drain holes there to let the water out, and not to mount the lights upside down because of this. It's a shame, because the optics produce a beam that is one of the best, in my opinion, for spread, intensity and penetration.

Thanks for the info Rowan... I haven't had a chance to look closely at the switch, but I had a sense that I wouldn't really be able to disassemble or clean it.

Fortunately I bought the light at a local shop, so warranty service might not be so far-fetched after all. And at any rate, the auto mode is working fine for the time being.

Is it the Lumotec Oval Plus Senso? If so, I think that's actually a grounding problem.

THE PROBLEM
The Lumotecs (all of them) use a twin cable to connect to the generator. It works perfectly when used with the completely isolated Schmidt dynohub, but alas, the Shimano dynohub has contact with the mass.

The round Lumotec works fine if you wire it correctly, but the condensor in the Oval Plus makes it problematic. It either works all the time or never works at all. It's likely that your old fork had insulating contacts and that the new one has none, so that you have two routes for the current. Insulating the light should solve the problem.

THE SOLUTION

Install the headlight on a piece of plastic tubing like a short section of plastic conduit. Just make sure that there is no metal to metal contact between the headlight and the metal parts of the bike. It should then work properly.

Is it the Lumotec Oval Plus Senso? If so, I think that's actually a grounding problem.

THE PROBLEM
The round Lumotec works fine if you wire it correctly, but the condensor in the Oval Plus makes it problematic. It either works all the time or never works at all.

It is an Oval Plus Senso... but it works some of the time, which is the confusing part. Though I suppose it's possible that the contact through the fork isn't very good, and thus the grounding problem comes and goes as things wiggle around.