Questions? Looking for parts? Parts for sale? or just for a chat,

The WD Motorcycle forum

WD Motorcycle forum
Start a New Topic 
Dynamo issues and problem - Updating

Dear all,
After all I went through with my charging problems, I can finally state that I managed to find the problem, fix it and I would like to share as for the future to come, if someone will have the same sh**t as I had. As I mentioned, the dynamo was sent about 10 years ago to a well-known specialist in the UK, for a total rebuild. I remember that it cost me a fortune, and that I had lots of bureaucracy with the local crazy customs authorities that wanted to charge me like hell when the dynamo will enter back to IL, but then again – the guy was a well know specialist who was highly recommended over here on the forum. He did make a good job, but all the contacts of the wires attached to the commutator became loose, as he only pressed or squeezed them to place, in some way (looked like a poor spot welding), not soldering them. So, as they have become loose they were still on place in position, fooling me, as the current could not flow steadily.
The genius who got it and solved the manner was my father in law, who was also hired to try to solve the issue. He sat one afternoon in front of the rotor, starring at it, thinking and thinking. Then he went to bring a screwdriver, and tried the contact quality of those wires. They all became loose of the commutator. So he soldered them one by one. Now I have a current of 12 volts and more, steady as a locomotive.
Thank you all.

Re: Dynamo issues and problem - Updating


When the dynamo becomes too hot the solder will melt and be thrown out. Didn't you find small silver chips in the band that is clamped at the end of the dynamo. If so it probably was soldered originally but because of over charging it will have overheated and shed all its older.

Kind regards,

email (option): leonhop3_at_planet_dot_nl

Re: Dynamo issues and problem - Updating

Hi Leon,

Out of interest, how does a dynamo overcharge and what prevents it from overcharging?



email (option):

Re: Dynamo issues and problem - Updating

Anyone, please correct me if I am wrong on this!

The output of the dynamo depends on how fast it is rotating and the strength of the magnetic field generated by the field coils. Some of the output is fed to the field coil windings to maintain the magnetic field and this is controlled by the voltage regulator which ensures that as the speed of rotation increases the field is reduced to limit the output to the desires level (6V).

As the engine speed varies the field coil voltage is adjusted to maintain a constant output.

If the voltage regulator isn’t doing it’s job the field coil voltage can increase and you have a feedback situation where the voltages shoot up. Then the dynamo overcharges, overheats and becomes an unhappy dynamo.

Have a look at this website for more/better explanations and under the rewinds & repairs sections it lists common problems.


email (option):

Re: Dynamo issues and problem - Updating

So will it be ok to install a fuze between the regulator and the dynamo?

Re: Dynamo issues and problem - Updating

Hello Michael,

Usually there is no need of a fuse on the regulator line,
And originally there is no fuse in the system.
Anyway, a fuse would not prevent overcharging.
(As Leon mentioned, an overcharge at the past probably caused the commutator soldering to melt)

If you want to install a fuse, I would put one on the main lead to the battery.
(Can be the negative line to the chassis or main positive- will work the same)

Th correct value would be a bit over the maximum normal current (Amp) consumption
By the formula:

I= Current in Amps
P=Power in Watts
V=Voltage in Volt units.

So if your headlight is 18W, for example, and rear lamp is 21+5W,
You are already at 44W, which is 44W/6V=7.4Amp
So for this EXAMPLE 10A is OK, (We did not consider the horn, if it fused)
And anyway,
If the same fuse is also going to the feed from regulator to battery,
You need at least 10A fuse, to cover the maximum theoretical charge.
So a 10A fuse should be OK, and to be on the safe side, I guess 15A will also protect from a short-current.
(We do not add the consumption value to the charge value,
As they flow in different directions- one to the battery and one from the battery,
so the difference is deducted)

Hope it helps.

email (option):

Nieuwe pagina 1