Generac — Constant (Fixed) Excitation Test
Testing & diagnosis · Rotor / Voltage Regulator circuit
From a Generac service manual covering: IM100G, IM80G, NP100G, NP80G. Check it applies to your exact model before use.
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Procedure
- Shut the generator engine down.
- Connect a voltmeter to the generator's AC output leads.
- Disconnect Wires No. 4 and 1 from the Voltage Regulator.
- Connect a jumper from terminal #1 (Wire #15) of the engine control circuit board to the terminal end of Wire #4.
- Connect a jumper from terminal #2 of the engine control circuit board (Wire #0, ground) to the terminal end of Wire #1.
- Start the generator and let it run at no-load (breakers open) and rated speed.
- Read the AC output voltage; should be approximately one-half rated voltage (about 40-60 volts line-to-neutral or 80-120 volts line-to-line).
- Shut the generator down.
- Reconnect Wires No. 1 and 4 to the Voltage Regulator.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Reading approximately one-half rated voltage (about 40-60 volts line-to-neutral or 80-120 volts line-to-line)
Source: Generac service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.