Powerdynamo, checking PD AC regulator

Powerdynamo brings new ignition & light
to your vintage motorcycle



Technical Help



AC regulator defective? how can i check ?

For information on our DC regulators see here

The following information refers to our AC regulator (as shown here).

For more information on this regulator,  its use and its limitations click picture.

  • The shortest way to tell whether a regulator has gone is to smell on it. If the unit has a burnt smell it has surely gone (invariably due to shortcircuits or overloads)
  • the next easy thing is to start the engine and switch on headlights. If headlights shine brightly (at least when you accelerate a little engine revs) than the regulator is working

    should the regulator not smell and there be no lights whatsoever, than you have to dig a little deeper as suggested below. Please refrain from any other methods of testing, especially from connecting testing voltages from supplies other than the Powerdynamo magneto.

  1. You have to check first whether it is not the generator which is defective. without any output from the generator there is nothing to rectify and regulate.

    For this disconnect the 2 black wires which lead from the generator to the regulator.
    Connect here a meter that can read AC (!) voltage in the range 50 volts.
    Start the engine. The meter should indicate something between 20 and 50 volts - depending on engine speed). If you get no reading or significantly less the stator or the wires from the stator are defective. (regulator might be also defective, but you can not check now)
  2. Provided there is AC voltage from the generator, reconnect the 2 black wires to the regulator again and completely disconnect the middle pin of the unit from the rest of the motorcycle wiring 

    Connect a headlight bulb (in the correct voltage 6 or 12) directly to the middle pin and the metal holder (ground). Do not connect anything else there!

    Start the engine. If the bulb shines brightly (be careful not to look directly into the light, this will dazzle your eyes!) the regulator is working. If it does not (and you have rechecked wiring of the testing arrangement) the regulator has a problem.
  3. If you have the problem of bulbs beeing constantly blown, check what voltage the regulater delivers. For this connect a meter, put on AC 20V region directly to the middle pin and the metal holder (ground).  With engine running you should get between 14 and 15 volts. This voltage will change a little with lights switched on , but should stay below 15.

    If you get more, the unit is defective. (best indication however is whether the bulbs sustain or blow as a meter could be wrong)

    For information on possible fuse blowing and high current flowing if  lights are switched off, see here
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