It is important to address the most common causes of low or no output voltage, usually, 15V – 50V as measured at the generator terminals. Here are the steps to run the checks yourself.
To start, remove the connection box lid mounted on the top of the generator. This allows you to stare into the belly of the beast. See the image in step one.
Step 1 : Check Exciter Stator Continuity and Resistance
SAFETY NOTE – Exciter stator testing must be done with the generator off.
Disconnect exciter stator leads F+ & F- from the voltage regulator – red and black leads in the figure below. Using the meter, check the continuity between the F+ & F- wiring. If you have NO continuity between F+ & F-, you have a failed exciter stator winding.
Switch the meter to auto-ranging Ohms setting and check resistance between F+ & F- wiring. If exciter stator resistance does not match the specifications table value within ± 5 Ohms, this is also a failed exciter stator winding.
Step 2 : Checking Diodes / Rectifier Assembly
Your generator must be off to perform this test.
Remove the end cover from the generator to access the diode bridge.
The diodes may be tested in place. Remove the two main rotor leads (B) and the three exciter rotor leads (A) from the rectifier assembly (see figure). Note the location of each lead for proper reassembly. The diodes are now isolated from the generator and are ready to be tested.
Multimeter Diode Test: Switch the multimeter to diode test mode, place one lead on the top of a diode, the other lead in contact with the corresponding main terminal post. Test each of the three FORWARD diodes in turn. Reverse the test leads and repeat. A good diode will show no voltage reading in one direction and 0.4 – 0.5Vdc in the other.
Repeat the testing procedure for the three REVERSE diodes.
No voltage in either direction or voltage in both directions indicates a failed diode.
OR
Analog Meter: Place one lead on top of a diode, the other lead in contact with the corresponding main terminal post. Test each of the three FORWARD diodes in turn. Reverse the test leads and repeat. A good diode will have much greater resistance in one direction. Typical forward resistance is under 100 Ohms. Typical resistance in the reverse direction is over 30,000 ohms. Repeat the testing procedure for the three REVERSE diodes.
Continuity with little or no resistance in both directions or very high resistance in both directions indicates a failed diode. Failed diodes or the rectifier assembly will need to be replaced.
Keep in mind if your generator has been sitting for a long period of time in an area where there is a temperature variation and condensation you need to blow heat into the barrel through the end for a few hours to dry it out and remove any moisture laying in the bottom of the barrel at startup. If not, you take the chance of letting the smoke out of the unit.
Our next installment will cover what to do if your generator has sat for an extended period of time and you have zero AC Voltage output. This will be the constant excitation test or (Flashing the Fields). This one is exciting as you do the test with the generator running, so be careful!
