Tachometer/Alternator Problems??

[Bill Romeo]

I am the new proud owner of Sea Witch, a CD31. Over the past 2 weeks I have noticed that my tachometer was acting erratically - it seems to bounce up and down about 500-700 rpm's from it's correct reading. Initially this started happening at low rpm's, but it now occurs at all rpm's. Then last night while returning home after a great sunset sail, I turned my cabin lights on and noticed that the lights were surging from bright to dim. I will add that this only occurred once I was under power returning to port - the lights were normal prior to running the engine. Once I returned to my slip, I let the engine idle a low rpm's for a few minutes and the lights stopped surging. Is this an indication that my alternator (75 amp) is beginning to fail? It seems odd given that the alterator is only 5 years old with low hours. I would greatly appreciate any thoughts or suggestions.

Thanks, Bill

[Russell]

Having the altinator rebuilt is inexpensive and a good regular maintence thing to do. I would also take a close look at the regulator. I would guess your problem lies in one of these two things. Its also possible your batteries are shot or you have a wiring problem. It sounds like your altinator is fluxuating output rather rapidly.

I would do the following in this order:

Check all wiring, look for corroded terminals or old ugly wire. Check at the batteries, altinator, regulator, and grounding locations and any intermediate stops. Replace and clean if nessisary.

Check out your batteries, fully charged and unloaded are they showing the proper voltage? When my batteries began to fail I experienced a similar problem to yours (though the fluxuation was not so rapid).

If its not a wiring or battery problem, remove the altinator and have it rebuilt. Even if you solve the problem from wiring or something else, might as well do this anyways.

If none of the above does the trick you may need a new regulator. I would save this for last as they are not cheap. I doubt this is the problem though, my bet is on the wiring.

Russell

[Matt Cawthorne]

Did you check your belt tension? It may seem silly, but sometimes the most obvious are the things we overlook.

Matt