Bicycle lamp doesn't light up, why?
Hello everyone,
I just tried to repair my bike xD In the end it was just a matter of cleaning it again and replacing the rear cantilever brake.
Unfortunately, I can't get the front light bulb to light up. I was at a bike shop the other day, and the nice man there tried to explain to me what I should do, but I don't think I really understood.
So the setup looks like this: A classic dynamo with plus and minus connections, two cables, one from the front and one from the back, that come together at the dynamo and both plug into the plus terminal. (The guy at the shop said I probably don't need to connect the ground, since the dynamo's screw connection to the frame is sufficient.)
The rear light works without problems both twisted with the front wire and on its own, the front light not at all.
The bulb isn't broken, the man in the shop checked it, I also took apart the front connection and couldn't find any contact problems.
What am I doing wrong?
Thank you very much in advance.
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Yes, on a bicycle, the two poles are called positive and ground, or the live wire and ground. The fact that it's alternating current doesn't really matter. The circuit just has to be closed, as always.
Yes, the contacts are usually the problem. They tend to corrode. You can scrape them clean. If you've found a light bulb, it's also possible that the contact is bent too far back towards the end of the bulb. You can carefully bend it forward a bit. Have you tried using a battery to light the lamp?
Conducting the ground via the frame doesn't always work. The current doesn't flow through the paint. Other components, such as suspension forks and fenders, don't necessarily conduct electricity either.
Because there are three poles—the two regular terminals plus the dynamo's mount—it's easy to create a short circuit. The lamp, at least an older light bulb model, also has these three paths for current.
Some cables are also defective, although you can't see it from the outside, they are torn on the inside.
Use strict logic, and you'll get it right. Sometimes I manage it with a wave of my hand—the plug was unplugged—but sometimes it's taken me hours to find the problem.
Thanks, most helpful so far. I checked the metal on the bulb, but I suspect the cable inside is damaged. I can't think of anything else.
No, if you put both in one terminal you have created a nice short circuit
A dynamo has no plus or minus. It's an alternating current generator.
But that's what it says on the dynamo. xD
Classic bicycle electrical systems use the single-wire method: One wire runs from the dynamo to the lower contact surface of the bulb. The second wire isn't a wire or cable, but the bicycle frame itself. This is called "ground." Some even call the frame "earth."
Yes, mass is what the gentleman in the shop said, I didn't know that was the same as soil or the frame, thanks.
If TWO (2!!) cables come from a "bulb", they must either be connected to TWO (2!!) DIFFERENT terminals on the dynamo or only one to a dynamo with a single contact and one to the frame.
There is only one cable per bulb.
Does the cable from the bulb at the front need to be connected to the frame? Where does it get power from the dynamo?
If the bulb only has one wire, the second contact is made via the metal bracket on the frame. Therefore, your dynamo definitely needs a conductive connection to the frame, and with modern dynamos, a screw connection is NOT sufficient. A cable must explicitly run from one of the two contacts to the frame or the screw connection.
I already had the setup.
I wrote that ONE of the dynamo contacts must be connected to the frame via a cable. Both lights must be connected to the OTHER dynamo contact and each with its second cable to the frame.
I'll try again in detail:
The light bulb at the front has contact on the lower surface in the holder to a metal surface which is in contact with the bicycle frame via a screw connection (as I understand it, this should be the ground). On the screw connection of the bulb itself there is another metal contact to which the wire is clamped which should be connected to the dynamo + pole, then the circuit is closed, right?
Your entire description is ambiguous and unclear. A simple electrical circuit isn't rocket science. Draw it.
Then why is the rear light lit? Shouldn't that also not be lit?
I had previously connected an earth cable or, as I have already learned here, a ground cable, but nothing happened, not even the rear one.