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Old 03-05-2010, 06:50   #1
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Alternator and Tach Output Issue

I recently had two issues occur in the same day and I suspect they are common but I'm not sure. I have spent two hours reading alternator output posts but before I drive 2 hours with my troubleshooting list, I thought I'd ask for some advice here.

First, my tack and temp gauge normally read when I remove the ignition key (I'm not sure that is normal but it is for my boat). Suddenly, the both indicators stopped functioning (with the key removed). So I inserted and turned the key back on and both indicators returned to normal.

Seemingly (and possibly) unrelated to the ignition switch issue above, I realized the same day that my engine was not charging the batteries. When I got back to my marina and reconnected to shore power (after having discharged one to 12.2 and the other to 12.5), the charger ran at full capacity (15A) for the two hours I was there.

I'll be checking voltages, wiring, contacts, fuses, etc. when I go back tomorrow but it seems too coincidental that I'd have two electrical problems in the same day. Can anyone here provide any thoughts on how the two might be related or what the cause of my alternator not charging might be?

I'll post my findings.

Islander 30
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Old 04-05-2010, 13:47   #2
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Alternator Update

I checked voltages at the battery with the engine off. Then I started the engine and checked it again, both at the battery and the alternator. All voltages were essentially the same. Conclusion - no output from the alternator. It is a Marchel unit with an integrated regulator. I have lots of reading material but much of it is unit specific. I got cold feet and went to the marina mechanic. He told me to remove it and bring it over - that he would send it out and have it back tomorrow (assuming they don't have to order parts). When I took it off, I noticed that the D- lugs were a little loose internally. Also, there had been some burning in the rear of the unit. Not sure what or why but I suspect this has to do with no output. Any thoughts? I sure wish I had a schematic for the instrument panel (engine is a Volvo MD7A and panel is Volvo supplied). It has a weird fuse in line with the ignition switch and there is a light related to the switch also. The light burns dim all the time when the switch is on (engine running or not). I checked the resistance across the light and it readings vary (maybe it's more than just a light). I read that it might be some type of excitation device. Any thoughts?
I'll repost when it returns.
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Old 04-05-2010, 23:16   #3
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Location: Oceanside, Ca.
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You might have a bad diode in the alternator, so checking the alternator might be a good idea...might need it rebuilt. The light is most likely an exciter light, since your alternator has internal regulation. The light will stay on until the alternator is working. Check all wires and connections in the alternator circuit, and at the cockpit gauges for corrosion.
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