Precision Low Ohm Resistance Measurement.

I am repairing an Onan RV generator. It doesn't produce 120 volts AC output. Only 40 volts AC is generated.

I wanted to check the stator windings to verify that they are OK.

The problem is, the ohm readings are very low ohm. My volt-ohm meter only can read down to .1 ohm

That's not good enough to test the coils of a stator.

My BGEF 4 KW Onan generator has four windings.

T1/T2    =     .327 ohms

T3/T4    =     .327 ohms

B1/B2    =    .058 ohms

Q1/Q2    =    2.089 ohms

I checked at an electrical company that repaired motors, but they charge $30 to check things out.

After a lot of thought I realized that I only need two values to get an ohms reading. Volts and amps.
Most digital volt ohm meters can read from .1 ohms to infinity and .1 volts to 1000 volts.

Please look at the wiring diagram to see how it is hooked up.

By hooking up the meters to the stator coil you can easily and accurately the ohms of the coils.

You need two meters. Set one for 2 volt reading. Plug the probe wires in to GND  (ground) and Volts

Set the other meter to the 20 amp reading. Plug the probe wires to the 20 amp posts and GND.

Hook up the 10 volt .5 amp power supply to the stator circuit.

Theory of operation.

The coil is checked for voltage, the amp meter measures the amperes flowing through the stator coil.
Since the coil and amp meter have the same current and then by dividing the voltage drop across the coil then the resistance is calculated.

Formula is    R=E/I

R = resistance

E = volts

I = amps

My first reading was .040 volts and .69 amps. this calculates to .0577 ohms. This matches the .058 ohms the factory specifies. (B1/B2 coil)

My next reading was .242 volts and .75 amps. This calculates to .3226 ohms, very close for T1/T2 windings of .327 ohms.

My next reading was .239 volts and .73 amps. This calculates to .3273 ohms, very close for T3/T4 windings  of .327 ohms.

Q1/Q2 can be read by an ohm meter directly  2.9 ohms.