This sounds like I've an electrical issue, but no idea of next steps.

I have a Gazelle Tour Populair with what I believe is a Busch & Müller LYT Lumotec Retro front dynamo-powered light.

When starting to move the light comes on, but quickly cuts off for the rest of the journey.

The shop have already replaced the light with a new one, and same issue.

Could it be a power build-up somehow?

  • It's unlikely to be a power build up (as you put it), because the only way to store charge is in the light. Replacing the light should have ruled out a lot of potential issues. What type of dynamo do you have (hub, bottle,...)? I suspect that something is losing contact, either mechanical or electrical.
    – Chris H
    Oct 26 '18 at 11:44
  • It's a hub dynamo. My one other uneducated idea was that by fiddling with the light I'm earthing it, and then when I let go that something electrical is going wrong. I take your point about it could be a simple connection issue.
    – eoinoc
    Oct 26 '18 at 11:50
  • Do you have to do anything to make the light work again at the start of the next journey? Oct 26 '18 at 16:56
  • So my last journey had the dynamo light my full 2km journey. I locked it up. On the back it started to flicker and didn't come back on. Another journey, it did come back on after I opened the light (including the part that holds the bulb) and reattached it while moving slowly, which got it to light for a few more seconds.
    – eoinoc
    Oct 30 '18 at 7:45
  • Do you have the model with the "Senso Plus" ? if so, it might be an issue with the sensor. I have the same light with the senso plus, and my light goes out when an on-coming headlight hits my light at just the right angle but my light comes back on after the car passes. I have my light "ON" all the time to avoid that. Dec 7 '18 at 21:53

You could try measuring the voltage the dynamo outputs when spinning the wheel. Strip two thin wires on both ends , insert them into the dynamo plug (plug which is usually present on the hub to which the wire going to the light Is attached), attach a multimeter and spin the wheel. If the voltage drops to zero/drops considerably after a few seconds whilst still spinning the wheel the problem is not with the dynamo and it's probably a short circuit/ground or bad electrical connection somewhere.

Example of what a dynamo plug/ connector might look like: https://i.stack.imgur.com/fQyr8.png

  • Yes I do have a plug like that. I no longer have the multimeter. I'll try opening up that plug and make sure the wires are clipped into it properly.
    – eoinoc
    Oct 30 '18 at 7:49
  • 1
    @eoinoc Also make sure to clean the contact points inside the clip and on the connector (using something abrasive like scotchbright or some contact spray and a rag) Oct 30 '18 at 8:12

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