How to Test a Brushless Generator

Updated by Juan Velez

This covers the following Champion Power Equipment models: All 1200-1800W Generators.

Read instructions carefully and completely before performing service.

  • To reduce the risk of injury, user must read and understand the operator’s manual before using this product.
  • DO NOT make any adjustments to the generator without first stopping the engine and disconnecting the spark plug wire.
  • Burns from hot parts — let the engine cool completely before touching hot parts.
  • Injury from moving parts
  • To reduce the possibility of fire or explosion, be careful when working around gasoline. Keep cigarettes, sparks and flames away from all fuel‐related parts.
The regulation of the 120 voltage is maintained by the governed speed of the engine (approx. 3600 RPM) and is set with the throttle adjustment screw to give a frequency (Hz) of about 60-63 Hz for a satisfactory output level. 

Diagnostic Testing of the AC Voltage Electrical System

By using a common multimeter (VOM - Volts Ohms Meter) for the Volts-Ohms measurements, you can do a diagnostic on the AC output of the generator.

Test 1A

Remove the yellow end cover (vented cover over the generator) and unplug the four-wire plug with a red and black wire (AC voltage to outlets) and two orange or yellow wires coming from the exciter winding within the stator. Using the meter set to AC, connect each probe (no direction is required) on the two orange or yellow wires and obtain the reading. This test is performed with the engine running. A normal reading will be: yellow wires, 6.7 AC volts; red/black wires, 11.7 AC volts (+ or -5% for each). 

Test 1B

Reconnect the plugin connection and start the generator. Setting the volt meter to AC voltage, place your test probes on each of the yellow or orange wires and the reading should be about 150 volts AC. If this tests is to specs, then the condenser is functioning normally. You will not have to test any further or disassemble the panel cover. Your panel voltage should be at, or close to, normal (115V-125V AC).

Test 2

This test involves the remove of the four panel bolts and relaxing the panel assembly away from the chassis. On the backside of the panel is a black dust cover that is held on by two Philips screws. Upon removal of the screws, you will move the dust cover away from the panel and see a small, black box (condenser or capacitor) that the orange or yellow wires attach too. Remove any one of the two connections and for a microfarad test across the terminals of the condenser. This test will set your meter to an icon that looks like a "uF." Usually, a mode position of the Ohms scale which is a "horseshoe" looking icon. The result should be at about 11-12 uF (microfarads) + or - replaced. 

Test 3

With the generator running, you need to set your meter to AC and then place on probe on each blade terminal at the AC outlet on the front panel. You should have a reading between 115 and 125V AC. Adjust this range with the governor adjustment screw about the recoil housing of the start rope. Due to the condenser-style excitement use on this model generator, you will notice a somewhat unstable view of the AC voltmeter to give a solid hold at any particular setting. Turn it until a happy medium of this voltage range is determined. Of course, 120 VAC is the most desirable medium setting. Do not be disappointed if your setting is only close to this number and any slight movement changes the setting. A little trial and error will work for your setting. 

Static Testing of the Stator and Rotor

Stator Testing

With the nylon plug disconnected under the yellow cover, an Ohms test can also be performed on the stator. Using the probes of the VOM, and touching them to the ends of yellow or orange wires, you will get a result of about 5.88 Ohms + or - .2 Ohms. Outside of this range will indicate a failure of the stator's exciter field winding. 

Now, you can test the red and black leads at the nylon plug on the stator. This test should give a positive results of 1.05 Ohms + or - .2 OHMS. Outside of this range will indicate a failure of the main winding of the stator. 

Rotor Testing

You will note that the ends of the field winding wires include a resistor between them. If the resistor is tested in place, the reading will be about 8.7 Ohms + or - 5%. If the resistor is removed, the test will show about 10 Ohms when tested at the ends of the field winding wires. Any numbers outside of 5% of this test will indicate failure of the rotor and a replacement will be necessary. 

View and download the PDF version here.

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