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Halfway through my third winter my Lumotec IQ Fly Senso Plus (powered by a SON hub-generator) headlight has suddenly started fluctuating, after I returned from Christmas holidays. While riding in the dark (and darkness lasts 20/24 hours here this time of the year), my light semi-regularly switches from bright to faint and back to bright. The faint light looks like the standlight, so very much less than the bright light. I ride in the dark around 5 hours/week during around 5 months, so with around less than 500 hours of dark riding, the LEDs should still be fine — or do LEDs degrade much more quickly in the cold (<-20°C)? My own hypothesis would be as mentioned on this forum:

The flickering of the previous light could have been caused by adjusting the light when it has been firmly screwed down. This could cause the contact lip to turn in the housing and loose contact with the bulb. If this happens bend the lip forward again, and ease the mounting bolt a bit before readjusting

but I'm not sure if it applies to my model, I don't know what lip to bend forward and how. I've already firmly attached the plugs on the outside, but maybe something got loose on the inside. As I'm a bit afraid of starting to disassembling things I can't assemble again, I'd need some advice.

  • What can I open, firmly attach, adjust, etc. in an attempt to tighten all connections that need to be tight, and how do I do this?
  • What other problems may cause the observed behaviour, and how would I handle those?

(also posted at this Dutch forum)

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First thing to do, of course, is to check all connections. Unplug/replug connectors, and loosen/retighten any screw connections. But what you're describing may be a failure of the sliprings in the hub. (Minus 20C is balmy -- just -4F.) –  Daniel R Hicks Jan 17 '12 at 23:04
    
I have currently been forced to put work on this on hold. Yesterday my bottom bracket loosened, and the bicycle is now in the local workshop waiting for a new one to be ordered and to arrive. The same workshop said that if a light is poorly functioning, they don't open and fix it, but only replace it. In any case, for at least the next week I won't have my bicycle so I can't test anything suggested here :( –  gerrit Jan 19 '12 at 15:35
    
This makes me think that the lamp was somehow damaged by winter temps. Unfortunately I have no idea how to fix it. Like I suggested above, it's very likely that the problem is due to the sliprings in the dynamo. Unfortunately, the SON hubs do not admit to being serviceable. –  user3671 Mar 15 '12 at 16:55
    
Also check the position of the switch, I had a similar problem and the switch was halfway between the senso setting and on causing an odd behaviour –  Rider_X Dec 28 '13 at 21:48

3 Answers 3

up vote 2 down vote accepted

Since it is an halogen light (correct me if I'm wrong), there is a socket inside, with a spring or something, where you "screw" the lamp. Maybe the spring got weak, there is some rust, or some other sort of bad-quality electrical connection.

Since the lamps are meant to be replaceable by the user, you could do it yourself perhaps without any tool, or perhaps with a small screwdriver or some sort of tiny plier.

If you are in doubt, you could take the light to some friend or shop to take a look inside, for obvious bad-connections caused by rust or misalignments. A simple cleaning would do it, the lamp connections are always quite similar.

The forum refers to adjusting the light angle, twisting the whole headlight, while it could be too tightly fixed on the bike. That would mean the headlight outer casing and/or internal structure got a little bent and misaligned. A movement in the oposite direction coud straighten things back to normal, perhaps.

Hope it helps.

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The Lumotec IQ Fly Senso Plus is a LED light. bumm.de/produkte/dynamo-scheinwerfer/lumotec-iq-fly.html –  Paul Weber Feb 20 '12 at 15:48

Recently my Lumotec IQ Cyo T senso plus powered by Shimano hub DH-3D30 also started flickering in the same way as you described after I rode in severe cold (-20C). Your lamp is very similar to mine. Initialy I suspected hub, but your hub is different. However we both have Lumotec LED lights and used them in frigid temperatures. This makes me think that the lamp was somehow damaged by winter temps. Unfortunately I have no idea how to fix it.

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Mine was solved by twisting the lamp back, so it was a poor connection. Another suggestion I saw somewhere is that it's just the light-sensor and putting the light on 'always on' rather than 'autodetect' would help. –  gerrit Mar 14 '12 at 10:44

Like I suggested above, it's very likely that the problem is due to the sliprings in the dynamo. Unfortunately, the SON hubs do not admit to being serviceable.

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