Generac — Testing the Battery Charge Circuit
Testing & diagnosis
From a Generac service manual covering: GN-190, GN-220, NP-30G, NP-40G. Check it applies to your exact model before use.
Applies to: Generac NP-30G, Generac GN-190 / GN-220 engine, Generac GN-220 engine
Procedure
- Disconnect Wire 77 at the Battery Charge Rectifier (BCR).
- Disconnect Stator output Wire 66 at the BCR.
- Disconnect Wire 55.
- Set a VOM to Rx1 and zero the meter.
- Connect the VOM test leads across Wires 77 and 55, then across Wires 66 and 55; note both resistance readings.
- With the unit running, measure AC voltage at the Wires 66 and 77 terminals; if no AC voltage, an open circuit exists in Wire 66 or 77.
- With engine running, check for DC voltage between the BCR Wire 55 and frame ground; if AC was present but DC is not, the BCR is defective.
Tools required
- VOM (volt-ohm-milliammeter) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Battery charge winding resistance across Wires 66 to 55 = 0.037-0.042 ohm
- Across Wires 77 to 55 = 0.037-0.042 ohm
Full service-parts list: Generac NP-30G →
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.