dt125a&b starter/generator

[chopwatchagot]

Hi everyone!
I'm new here so I don't really know my way around yet. I'm wondering if anyone here has any experience with the 1974-75 dt 125a & b starter/generator units. They are kind of wierd in that when current (from battery) is applied it is a motor to start the engine and once the engine is running it is a dc generator (not a magneto) to power everything. I have ordered a manual but it hasn't arrived yet but I would like to do some tests. The coil is good, the points are good, the condenser is suspect and I don't know if the gen. is putting out any juice at all. Any help would be greatly appreciated.

Dean

 

[rmc_olderthandirt]

I am not familiar with the bike at all, but I do know a bit about electric motors and generators.

There is really very little difference between a DC "generator" and "motor". There is a stator that creates a magnetic field (either from permanent magnets or a coil with current flowing through it) and a rotor that turns inside it. The rotor has a "commutator" that switches between multiple coils as the rotor turns.

Connect it to a battery and the rotor will want to turn. Resist it from turning and it will draw a lot current from the battery. Let it turn freely and the current is very low. Force it to turn a little faster and the current goes to zero. Turn it even faster and it generates electricity instead of consuming it.

I am guessing that your need to know is because it isn't working.

If it doesn't work as either a motor or a generator then I would suspect that either the brushes are bad or a winding has burned out. Commutated motors really wear out brushes fast so I would suspect them first.

As the rotor turns and the brushes work there is usually a small amount of arcing. This can eventually eat at the commutator and create bad spots. Ending up with a dead spot on the commutator can keep the motor from starting if it happens to stop at that spot, or just really reduce the effectiveness of the motor or generator if it manages to keep turning.

If it works okay as a motor but not as a generator then I would look for a voltage regulator problem.

Rod

 

[chopwatchagot]

Thanks

Hey Rod

Thanks for the info/lesson on generators :nod: I checked the brushes first and they were stuck but with a little Wd40 they loosened up so the springs would keep them in contact with the commutator (?). Viola! It works. I think the 30 year old condenser needs to be replaced but I have an idea that the bike will fire after that. Thanks again for your in-depth response.

Dean