Dynamo Trouble: Sporadic lights, double brightness

p

Hey all,

Anyone here good with dynamos?

I've got an old school dynamo (not LED) on my city bike and having some odd results. Sometimes only the front light comes on, and sometimes only the back light comes on, and usually with double brightness. I've opened the dynamo, and then just connected either the front or back light, but then they don't work at all.

I guess there's some kind of loose connect somewhere, but thi behaviour has me confused where that might be.

Any tips or what it might be, or how I can track it down?

Cheers

Kevincavan83

Any tips or what it might be, or how I can track it down?

Cheers[/quote]

Dynamo is pretty simple, check youtube for videos.
You'll need a digital multimeter though for checking the resistance of coil and for the output voltage.
Might be coil is broken or your magnet is dirty/rusted

CramCycle

p wrote: »

I've got an old school dynamo (not LED) on my city bike and having some odd results. Sometimes only the front light comes on, and sometimes only the back light comes on, and usually with double brightness.

Back lights use alot less voltage, sounds like it might be taking to much power.

I've opened the dynamo, and then just connected either the front or back light, but then they don't work at all.

Is it a hub dynamo or a rim wall dynamo?

I guess there's some kind of loose connect somewhere, but thi behaviour has me confused where that might be.

Could be the wiring corroded somewhere as well. How old is the cabling, was it fully sealed? The fact that is not consistent screams to me that it is corrosion on the cabling potentially coupled with corrosion at the contact points.

Any tips or what it might be, or how I can track it down?

pics would be a good start for comments, see what the set up is and what it could be.

Al Wright

(Tyre sidewall) dynamos usually use a single wire to lamp with earth (bicycle frame) return. With this system a bit of rust at the fittings, dynamo bracket, lamp bracket etc. can cause problems. The connections to dynamo and lamps are usual simple bared flex bent into bulb holder, this connection might not be good, flex insulation getting in the way a wayward strand of wire causing intermittently shorting.
The connections to the old style hub dynamos are via small bolt/nut setup, sometimes the flex is fitted with crimped eyelets, check for loose/broken flex similar to above.

p

Hey - thanks for all the useful feedback.

Since I posted it now only the front light is on - haha!

It's a rim wall dynamo.

I've a multi-meter in work I can borrow, so i'll try that out. The contacts all seem pretty solid, but i'll give them a little sand, and check all the seal, and also check where it's being grounded.

I'll let you know how I get on

cdaly_

Don't forget the ground contact screw on the dynamo mount. It should press a point through the paint on the fork to make a metal to metal contact. Also, grease any contacts that you sand.

p

Hey all,

Just wanted to followup on this. Took all your advice.

Eventually just replaced the wires copletely and got it working. Seemed I also had some problems with the ground too so that required a bit of TLC, and I also had a shot bulb. Crazy!

All working a treat now again! Appreciate the pointers, they helped immensely.