Dynamo problems
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ACCG
Dynamo problems
I have dynamo powered lights that are a couple of years old. The front light illuminates for the first few seconds when I get on the bike but then quickly dims to a very low level. It doesn't seem to be a loose connection, but it is difficult to know this definitively as the rear light has a capacitor such that it stays illuminated if you stop for a short period. Could it be a problem with the dynamo or the bulb (halogen) getting old? Any help appreciated....
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jb
Re:Dynamo problems
Hi
Your dynamo isn't slipping on the tyre is it? a worn pulley wheel or worn dynamo track on the tyre could cause the problem stated.
Failing that disconnect the rear lamp and see if the problem is still there.
Failing that remove lamp from bike
and run separate earth and then spin the wheel to see if it works.
Failing that change bulb.
Failing that you might have an internal dynamo fault such as the magnet is loose on the shaft - steal your mates dynamo and see if it will run your lamps. if it works bin yours and buy new - repairing old dynamo’s never works and just causes heartache and pain and possible suicide.
Best of luck
Your dynamo isn't slipping on the tyre is it? a worn pulley wheel or worn dynamo track on the tyre could cause the problem stated.
Failing that disconnect the rear lamp and see if the problem is still there.
Failing that remove lamp from bike
and run separate earth and then spin the wheel to see if it works.
Failing that change bulb.
Failing that you might have an internal dynamo fault such as the magnet is loose on the shaft - steal your mates dynamo and see if it will run your lamps. if it works bin yours and buy new - repairing old dynamo’s never works and just causes heartache and pain and possible suicide.
Best of luck
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Pedalling Pete
Re:Dynamo problems
Slipping dynamo sounds possible - is the dynamo aligned along a line from the hub to rim? If at any angle you will get problems. Is the pressure against tyrewall correct?
You don't mantion dynamo make, but should have twin wired cable to ensure earth return is through the cable, not the frame which caused problems in old designs.
I agree that opening the dynamo probably fruitless, but it worked for me once: Voltage was present, but not enough current for bulbs. Inside I found a large brown crystal had grown in the concave dish used as spring contact on closing the dynamo. Winter rock-salt in the water from the road had entered the dynamo, and the heat had driven off the moisture to leave the crystal to act as a resistance to the current. After removing the crystal all worked OK!
I now use the new LED based battery lamps from Cateye for reliability and redundancy, with one front and rear and supplementary flashers.
You don't mantion dynamo make, but should have twin wired cable to ensure earth return is through the cable, not the frame which caused problems in old designs.
I agree that opening the dynamo probably fruitless, but it worked for me once: Voltage was present, but not enough current for bulbs. Inside I found a large brown crystal had grown in the concave dish used as spring contact on closing the dynamo. Winter rock-salt in the water from the road had entered the dynamo, and the heat had driven off the moisture to leave the crystal to act as a resistance to the current. After removing the crystal all worked OK!
I now use the new LED based battery lamps from Cateye for reliability and redundancy, with one front and rear and supplementary flashers.
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jb
Re:Dynamo problems
Yes Petes correct,
the side wall pressure against the tyre wall is the most likely candidate (assuming were talking about a bottle dynamo), if the spring has gone weak or the bracket has crept away from the tyre this would result in initial light followed by going dim when the pulley started to slip.
The pulley should be about 5mm clear of the wheel when pulled off.
If you can push the dynamo against the tyre with your hand whilst your riding this will tell you if this is the problem. but if you fall off doing it I'll admit nothing.
the side wall pressure against the tyre wall is the most likely candidate (assuming were talking about a bottle dynamo), if the spring has gone weak or the bracket has crept away from the tyre this would result in initial light followed by going dim when the pulley started to slip.
The pulley should be about 5mm clear of the wheel when pulled off.
If you can push the dynamo against the tyre with your hand whilst your riding this will tell you if this is the problem. but if you fall off doing it I'll admit nothing.
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ACCG
Re:Dynamo problems
Thanks for the replies - I had already checked that the (bottle) dynamo was being driven by the wheel correctly! I think it is more of an electrical problem. Incidentally my wife has the same dynamo and lamp system and the same problem....
How do I know what sort of earthing system I have?
How do I know what sort of earthing system I have?
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jb
Re:Dynamo problems
If you only have one connection on the dynamo then it will earth through the frame via the bracket. More modern quality dynamo's have two terminals - one marked with the standard earth sign (some might have four terminals - two for each light) but they will also earth through the bracket usually. but like PP said it is best to run a twin cable to each light, but make sure the positives are the same on each lamp or a short will result.
Even though the pulley is correctly set up and looks to be spinning, it can still be slipping causing voltage drop, specially at this time of year when a lot of grease is picked up off the roads from fallen leaves. I eventually went on to a hub generator because of this so no more problems. but its an expensive option and depends on how much night riding you do.
CJ has some good stuff on setting up dynamos - better explained than me - some were on the CTC sight I think.
good luck
John
Even though the pulley is correctly set up and looks to be spinning, it can still be slipping causing voltage drop, specially at this time of year when a lot of grease is picked up off the roads from fallen leaves. I eventually went on to a hub generator because of this so no more problems. but its an expensive option and depends on how much night riding you do.
CJ has some good stuff on setting up dynamos - better explained than me - some were on the CTC sight I think.
good luck
John
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Jon
Re:Dynamo problems
For what it’s worth, I had a similar problem with a dynamo system. It was working fine until I installed a new rear lamp with a battery powered (not a capacitor) stand-light. The rear light was supposed to run off the dynamo while moving, and switch to the battery when stationary. It worked fine, but for some reason I was never able to fathom it sucked all the life out of the front light, which wasn’t half as bright as it was. The problem was definitely the new rear light, as when I put the old one back on everything was fine again. I would suggest trying to get hold of a different rear light and testing with that.
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CJ
Re:Dynamo problems
Most likely slipping pulley, but still turning slowly like jb says, especially as your wife's bike does the same. Fit a rubber pulley cap – or a better dynamo. Some dynamos, those that swing (like a door) toward the tyre rather than tipping over, drive better if mounted facing backwards on the opposite side of the bike.
A possible long-shot, if you have a one-wire system and the dynamo is at the rear, is a poor earth return due to old grease in the headset. I had this once: everything worked fine except that the headlamp, just the headlamp, flickered off and on when I steered. This puzzled me for quite a while. I checked everything, then I realised: with a back-pedal brake and a plastic brake lever and gear shift, the headset provided the only conducting path between frame and fork, and I hadn't checked it in years. So when the each ball rolled half a step sideways onto the adjacent lump of dried-out grease – the light went out – then on again once it reached the space so recently vacated by its neighbour. I re-greased the headset and all was well.
Needless to say: double-wiring puts an end to such perplexing puzzles.
A possible long-shot, if you have a one-wire system and the dynamo is at the rear, is a poor earth return due to old grease in the headset. I had this once: everything worked fine except that the headlamp, just the headlamp, flickered off and on when I steered. This puzzled me for quite a while. I checked everything, then I realised: with a back-pedal brake and a plastic brake lever and gear shift, the headset provided the only conducting path between frame and fork, and I hadn't checked it in years. So when the each ball rolled half a step sideways onto the adjacent lump of dried-out grease – the light went out – then on again once it reached the space so recently vacated by its neighbour. I re-greased the headset and all was well.
Needless to say: double-wiring puts an end to such perplexing puzzles.