Posted: Sun Dec 18, 2005 10:45 am Post subject: Help victor fb with dynamo worries
My batteries not charging. With the ignition on i read 0.8v on one contact of the dynamo and 0v on the other. Once the engine is started and reved the ignition light stays on and both contact are measuring around 1.8v.
i've been told it could be either the dynamo or the regulator. Can anyone expand on this?
If you wish to test a dynamo correctly, then the easiest way to do it is with a test lamp. With the dynamo disconnected, connect BOTH terminals to one lead, and the other to earth. Now start the engine, and increase engine speed slowly. The bulb should light up to full brilliance. If it doesn´t, or only lights dimly, the dynamo is at fault. Dont rev the engine to much, or the bulb will blow!
Yes this is the correct way to test a Dynamo, but if your Dynamo is one of the old type Bosch ones, it regulates on the negitive side and if you test it the same way as a normal Dynamo ie, connect F & D together to one side of a 50 watt bulb then the other side of the bulb to earth it will not out-put and you may think it is US when in fact it maybe ok.
IF it is one of the old type Bosch Dynamos the way to test it is as follows;
connect terminal D to one side of a 50 watt bulb then earth the other side of the bulb, then having done this; earth the F terminal on the Dynamo at the same time, if it lights the 50 watt bulb to full brightness or over brightness as to blowing the bulb, then its safe to say its in full working order.
I would just like to say, i have a 1944 vehicle electrical manual and it has the full info on the third brush Dynamo and how to set up the out-put ie, ajusting the third brush ETC, as this type of Dynamo has no voltage or current regulator, it is regulated by the third brush and field resistors in the vehicle lighting switch ETC, this is the only way they could stop the Dynamo cooking the battery in the good old days.
If you can get to the points in the regulator, you could try cleaning them up with a small file. If the points are badly pitted, you might have to find another regulator, as the problem will soon come back.
Yes, good idea to file the points as you said but please remember that by doing this you may have to re-ajust the voltage regulator voltage setting, its easy, all you need is a volt meter and small screwdriver.
Another way to check a dynamo after the above checks is; to see if the dynamo will motor, connect a positive supply to the D terminal (possitive output) and negitive to the earth (casing) the dynamo will should motor (turn very slowly like an electric motor.
Just a main point; if a dynamo has been stood for many years, it may have lost its res-magnetisum, in which case it may be a good idea to flash the dynamo if it fails all these tests, this could be the actual problem !
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