Dynamo terminals

[Maz]

The dynamo on this bike isn't working. As I don't know the first thing about dynamos, I'm assuming that the problem is that both wires go into a single terminal at the dynamo. Here is a picture:

There is a slot on the dynamo [opposite the terminal in use] like it should have a second terminal attached. Has this dynamo been wired up wrongly? What do you think?

[yes, the dynamo wheel is pressing/rotating against the wheel!]

Thanks.

 

[PatrickPending]

I believe the body of the dynamo is earth -the other terminal in effect so you only have the one wire coming out. check it with a meter on ac setting

by both wires i assume one gowes to the front and one o the rear light - thatd make sense

 

[Maz]

I believe the body of the dynamo is earth -the other terminal in effect so you only have the one wire coming out. check it with a meter on ac setting

by both wires i assume one gowes to the front and one o the rear light - thatd make sense

Yes, one wire goes to the front and one to the rear light. If it's working, should the lights come on more or less instantaneously? I dont think this bike has been ridden for months.

 

[RedBike]

For any bulb to work you need to have both a positive and negative "wire".
However, just to confuse things, a lot of cycle dynamos use the bikes frame as one of these "wires".
It is highly likely that the bracket of the dynamo is infact the negative connection.

I would start off trying to eliminate things.

Get a scrap of normal bell/speaker wire and connect it to your front light.
Test the light using two AA batteries.

Conect your speaker wire to the dynamo. One connection to the terminal, the other to the bracket.

 

[RedBike]

Yes, one wire goes to the front and one to the rear light. If it's working, should the lights come on more or less instantaneously? I dont think this bike has been ridden for months.

It all depends on the dynamo / light in question but they normaly start to glow at walking pace (instantly). Just turning the wheel by hand might not be quick enough.

The capacitors take 2/3mins of riding to charge but they shouldn't stop the light coming on straight away.

 

[Maz]

It all depends on the dynamo / light in question but they normaly start to glow at walking pace (instantly). Just turning the wheel by hand might not be quick enough.

The capacitors take 2/3mins of riding to charge but they shouldn't stop the light coming on straight away.

The dynamo is a Basta Duo. It really is a BastaD cos it's not working.

 

[PatrickPending]

I'd get a multimeter - check the output from the dynamo to see if its there (one lead on metal part of dynamo body the other on the terminal) - set the multimeter to AC voltage/ approx 20V range - if this is ok took at the voltage at the terminals. Check continuity of earth (dynamo body to other metal part on bike) and also continuity of the wires to the bulbs. Digital multimeters are dead cheap nowadays if you don't have one (try Maplins)

 

[Maz]

Thanks, PP. I think we've got a few Fluke multimeters at work. Could borrow one of them.

 

[twentysix by twentyfive]

Sometimes the earth connection via the dynamo bracket/frame/lamp mounting fails because their is corrosion on the mountings or frame. Electrically it's a cr&p but cheap way to make earth connections. Personnaly I'd "hard wire" a proper earth connection directly from the dynamo to each lamp.

 

[tyred]

Sometimes the earth connection via the dynamo bracket/frame/lamp mounting fails because their is corrosion on the mountings or frame. Electrically it's a cr&p but cheap way to make earth connections. Personnaly I'd "hard wire" a proper earth connection directly from the dynamo to each lamp.

+1

Wire each lamp with two wires. Speaker wire is a neat way of doing this.

Trying to make it earth through the frame is a pointless exercise. You need to scrape the paint to make a decent connection. Bare steel + moisture = rust = bad connection.

 

[actonblue]

I would also recommend adding a second earth wire. I run one from the rear light to the frame and I secure it with a rack bolt and a ring connector(I don not think that it is the correct name). The front light is mounted to the fork crown and the metal bracket makes a good earth.
Every so often(less than once a year) I will need to make sure all the points that the dynamo system make contact with the frame are clean from road grime, this will ensure a good earth.

 

[Maz]

Thank you for your help.