I have a 1989 JD 318 with a P218G engine. While using it today the charging indicator light came on and would not go off. The battery is always on a maintainer when not in use, and is fully charged at 12.6 volts. When I measure the AC voltage across the two wires from the alternator that connect to the two outer terminals of the regulator, I have 42 VAC with the engine at full throttle. When I run a continuity test from a ground to each lead to the alternator (each of the two outer connections on regulator) it shows infinite (no ground). With all three wires connected to the regulator, the center regulated output has no voltage (actually -.1 VDC). It appears to be a regulator issued. Anything else I should check before replacing it? Thank you for your assistance.
tjaltz
JD 318 Charging Problem
I have a 1989 JD 318 with a P218G engine. While using it today the charging indicator light came on and would not go off. The battery is always on a maintainer when not in use, and is fully charged at 12.6 volts. When I measure the AC voltage across the two wires from the alternator that connect to the two outer terminals of the regulator, I have 42 VAC with the engine at full throttle. When I run a continuity test from a ground to each lead to the alternator (each of the two outer connections on regulator) it shows infinite (no ground). With all three wires connected to the regulator, the center regulated output has no voltage (actually -.1 VDC). It appears to be a regulator issued. Anything else I should check before replacing it? Thank you for your assistance.
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My next step is ALWAYS to load test battery to see if a shorted cell is pulling voltage down.
Always make sure regulator is grounded to shroud when testing.... this is a must
If above doesn't give ~ 13.8 V or so at battery when running and connected, replace regulator.
My preference is spend a few bucks for OEM Onan part $45 or so.
When the ignition is turned on and the engine not running you should have battery voltage on the wire going to the center terminal. If you don't have such check for a bad fuse.
When you start the engine and run it at high rpms the center terminal voltage should go up above the static non running battery voltage.
If the DC voltage on the center terminal as read to ground don't rise above the battery voltage and you have 30Vac or higher reading terminal to terminal on the two outer terminals and the regulator is grounded good the reg is bad. (take the AC voltage readings terminal to terminal NOT to ground)
When you start the engine and run it at high rpms the center terminal voltage should go up above the static non running battery voltage.
If the DC voltage on the center terminal as read to ground don't rise above the battery voltage and you have 30Vac or higher reading terminal to terminal on the two outer terminals and the regulator is grounded good the reg is bad. (take the AC voltage readings terminal to terminal NOT to ground)
I have 42 VAC measuring across the two wires that connect to the outer terminals of the regulator. The regulator is properly grounded. I have battery voltage at the center terminal (obviously with the wire connected) and the voltage does not increase when the engine is started and run at full throttle.
Update - I replaced the regulator and it's working fine again. Light is out and it's charging the battery at 14.2 VDC at high throttle. Thank you all for your assistance.
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