GM 10 Intermittent Alternator Function

[jddj]

My GM 10 is going on 3 years. Last year, once that I noticed, the alternator was not putting out a charge to the batteries as indicated by the electrical panel voltmeter in the boat. When I first put the boat in a couple of days ago, I noticed that the Yanmar panel light did not show the charging light when I toggled the Test switch up. No charging voltage showed on electrical panel in the boat. Then after running hard for a while, the alternator suddenly showed a robust charge to both batteries on the electrical panel and the charge test light lit when the key key is on or the test toggle is up. I am curious to know what I should be looking for or what I should tell a mechanic to look for. I certainly don't want to be stuck somewhere with dead batteries I can't charge.

I have a Cape Dory 25D, hull #99.

thanks for any advice

jim

[Boyd]

I suggest checking for:

1. Loose electrical connection at the alternator, particularly the wire from the alternator to the battery positive.

2. Bad battery terminal continuity, corrosion, etc. althought this would probably be notice by the engine failing to crank.

3. Loose alternator belt, a very likely source.

4. Bad alternator ground, the case has to be electrically connected to the engine. Rust, corrosion where the alternator bolts to the engine mounting bracket, etc. I had this with a new alternator, paint was in the way.

5. Bad connection from the engine to the battery ground (negitive post).

You can take the alternator out and have it bench tested at an autoparts store for free.

90% of this you can test yourself with a simple multimeter. Test for voltage at the battery terminals while the engine is running, if the alternator is working you should find 14.4 volts +/- its not then 12.68 or less.

Good Hunting

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

[Al Levesque]

We once had an oversized cable from the alternator that had fatigued and gave us intermittent contact. In addition to the previous reply also try moving cables while running the engine to see if charging resumes.

[Mark Yashinsky]

from teh alternator case to the engine block and to the battery - post. From teh alternator output to the battery + post. If any of these show a voltage, you have a bad connection or wire somewhere along that path.