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Author Topic:   18 Volt Alternator Output, 1984 OMC V4 2 Stroke
bsmotril posted 05-10-2006 04:36 PM ET (US)   Profile for bsmotril   Send Email to bsmotril  
I have an '84 Johnson V4 Commercial 2 stroke rated for 100HP on a Montauk. This is the motor with the larger V6 15 spline gearcase. It came with Power Trim and Tilt, and I think I read that models with factory PT&T also had a voltage regulated alternator output. I also have a sealed black box mounted at the top of the exhuast cover between the heads, which is where a regulator is supposed to go.

With a recently replaced new battery, fully charged overnight with an automated 3 stage charger, I'm seeing 13-18 volts on the voltage meter in the dash when running the boat at cruise speed. This is with no accessory electronics running at all, no lights, no pumps. It cycles between 13-18 volts every 15 seconds or so, making me think the regulator is working somewhat. My question is; should the top end value of the alternator output voltage value be 18 volts? That seems kind of high to me. Is the regulator output adjustable in any fashion? Is 18 Volts output indicative of a bad voltage regulator, or some other problem with the alternator windings?


jimh posted 05-10-2006 07:46 PM ET (US)     Profile for jimh  Send Email to jimh     
Bill--I think a "regulated" charger output of 18-volts is too much. It sounds like the regulator has failed. I used to see that type of output on my OMC V6 when the regulator became warm and began to fail. I replaced it. Now I get a steady 14-volts from the motor.
bsmotril posted 05-11-2006 11:51 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I believe you're right. I finally found a test method in a service manual and it specifies 15 volts max output from the alternator if the unloaded battery voltage is below 12.5 volts. But since a new regulator is a little over $200, I'm going to do one more test run using a good Fluke VOM connected to the battery instead of assuming the dash mounted gauge is accurate. BillS
Chuck Tribolet posted 05-11-2006 12:19 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I can't see a high voltage being anything other than a
regulator problem. There's nothing in the alternator that
will make it fail with a HIGH voltage.

But check it with the Fluke.


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