le mans

I,ve always known this set up requires one wire

I needed an extra earth wire so the lights would work

can someone tell me why?


All the lights I removed from scrap bikes had one wire, and when I fitted lights to my road bike in the 70s it only needed one wire

The mind boggles

Moe Zhoost

Sometimes the dyno is grounded through the frame (one wire) and sometimes it isn't (two wires). Even if a 2 wire dyno is grounded to the frame (and I think most are), you would still need the second (-) wire if your light was not electrically bonded to the frame. I use coax for my dyno setups so I use one wire in every case.

daniell

I would think that the bike acts as the ground. It should not work on a carbon bike.

Andrew R Stewart 

Yes, the frame is the return ground wire. Look at the generator bracket on the fork blade and you'll see a screw sticking out. That screw has a pointed end that is meant to dig into the metal, under the paint, for that connection. The lights are grounded through their brackets too. And yes, this means that the current travels through the headset. Another reason to keep the headset in good shape.

BTW these bottle generator light systems can over power a bulb (some had 22mph max speed limits back in the day) and burn it out. A common story is the tail light burns out and the greater power the head light now sees burns that out soon enough after. Andy

JoeTBM 

this^^^^^^^^

JohnDThompson 

Yes, the ground screw on the fork blade clamp has to fully penetrate the paint and seat in the fork blade to provide a return path for the electricity.

unterhausen

some newer headsets have something non-conductive in the way.

Andrew R Stewart 

It is relatively simple to attach a wire to jump around the headset, and insure continuity. Andy

le mans

Ahh, I had forgotten what those little pointed screws are for

When testing I didn't screw it in, and assumed it's an added safety lock or something

Thanks Andy, I've always appreciated your help.
Now to get rid of that bulky wiring I got from an old kitchen appliance

le mans

BTW these bottle generator light systems can over power a bulb (some had 22mph max speed limits back in the day) and burn it out. A common story is the tail light burns out and the greater power the head light now sees burns that out soon enough after. Andy


Interesting, I must have had decent bulbs back in the day, I used to reach 35MPH, those mornings when it was still dark heading to work.

le mans

Nor an aluminum frame I would imagine

I have a Raleigh beach cruiser - aluminum frame that i'll fit lights on as well, that will probably need a earth wire.

Love these old lights.. I have a box full

I heard about magnetic generators, great idea, but I suppose you'd need steel rims to make them spin

Andrew R Stewart 

We ran a rubber cap on our generator tire rollers to quieten and slow down the unit. No mountains around here but we do get over 40mph often enough. Andy

GamblerGORD53

Those things were so useless, I seldom bothered, with or without the cap. There was NO way they ever went 22 mph, with 30% drag. LOL. I don't think the cap lasted 200 miles anyway. That's the exact setup I had.
About all they did was dig into the sidewall or not turn at all. What usually happened anyway, was you hit a bump and the front bulb filament broke, then the tail fried 20 secs later.
I had this happen while I waited for new lights for my SA dyno drum. The LED bulb I bought melted the plastic tail housing too.

JoeTBM 

An aluminum frame should be fine as the return conductor.

JoeTBM 

No sure if I have seen a headset that is fully insulated from the frame but there might be. If so Andy's thought about wiring around is a great solution.

JoeTBM 

No sure if I have seen a headset that fully insulated from the frame but there might be. If so Andy's thought about wiring around is a great solution.

alcjphil

Aluminum conducts electricity better than steel

soyabean

Just like automotive, the chassis the the ground.

Same with a lot of other small engines, like lamps for snowblowers.

The only time you will want to run your own (negative) ground wire is when you want more isolation for sensitive things, like zero-gauge for car audio amplifiers.

The amount of current coming from a vintage dyno that is needed to power an incandescent is plenty to overcome whatever resistance ohms you think a bike frame might make.

dsbrantjr

Many industrial bearings have (sometimes literal) brushes which short across shaft bearings so that current doesn't flow through them, as arcing from bearings to races can damage both.

sweeks

Not likely to be much arcing at 6 volts/3 watts (0.5 amp).