You can thank Marty Parson on the forestry forum for this advise.
Alternator Output Test Onan
1. Check Battery Voltage with engine not running. If not within specifications Charge Battery before Proceeding to step 2 VOLTAGE ON ALL MODELS IS 12 to 13 VDC
2. With engine Running, check battery terminal voltage ( Regulator Output) Using a DC Volt meter. Voltage output should be within the values specified. If voltage is greater than specified replace regulator- rectifier assembly. If voltage is less than specified proceed to step 3. VOLTAGE ON ALL MODELS IS 13.6 to 14.7 VDC
3. Examine all wires for loose corroded, or broken connections. Check fuses. Repair is needed to assure continunity between Regulator-Rectifier B+ terminal to battery positive (+) terminal. Also Check ground path from battery negitive (-) terminal to regulator-rectifier case. Make sure ground connections are clean and secure. If battery voltage remains low with engine running proceed to step 4
4. Disconnect Both AC stator leads from regulator-rectifier and test the AC voltage at the stator leads with engine running. If AC votlage reads more or less than specified in table 1 proceed to step 5. If AC voltage is as specified but DC voltage is low. Replace the regulator- rectifier. SPEC A 20 AMP ( Approx. 21 VAC @1800 rpm and APPROX 41VAC@3600 RPM Spec B 20 AMP Approx 29 VAC @ 1800 RPM Approx 57 VAC @ 3600 RPM ALL 35 AMP Approx 24 VAC @ 1800 APPROX 47 VAC @3600 RPM
5. Use the Rx1 scale on the ohm meter for detecting an open to ground in the stator ( unit not running) . Disconnect both AC Stator leads from the regulator- rectifier. Connect one ohm meter test lead to the stator lead, connect the other test lead to ground. Reading should show an open ( no continuity). If it doesn't the stator must be replaced. If the reading shows no continunity, measure the resistance of the stator windings by connecting one ohm meter lead to each lead coming from the stator. If resistance reading are as specified and winding are not shorted or open, Low AC Valtage may be due to loss of magnetism, If so, Blower wheel assembly must be replaced. SPEC A 20 AMP 0.06 to 0.10 Ohms Spec B 20 amp 0.10 to 0.19 OHMS 35 Amp 0.06 to 0.10 OHMS
Hope this Helps you guys. This is from the Onan engine service manual P216, 218, 220, 224
Marty
