Is it the alternator or the gauge

[Bayou Sailor]

Hi guys, My engine issues are 1000% better. Margarita runs like new and no exhaust issues. No smell, no smoke, GREAT. Now, I noticed that the ammeter not moving at all. It just sits dead in the middle. The gauge goes to +- 60 amps. How can I check to see if it is the gauge or the alternator? I looked at the electrical forum and didn't see anything. Any help?

[Al Schober]

Hopefully you have a digital voltmeter that you can trust. If not, get one.
Curious what your ammeter is supposed to read. Just alternator output, or does it measure all current in/out of your batteries. If the meter came with the boat, it's likely just alternator output. New (smarter) systems put a shunt in the negative leg to the house bank and measure current both ways. There are shunt meters that only do alternator output.
First step should be to measure the output voltage of the alternator, engine running. If it's more than battery voltage you should see charge current, hence a meter/wiring problem. If there's no/low alternator voltage you have an issue with the alternator or its regulator - don't confuse the two. Problems with either will prevent output from the alternator.

[Bayou Sailor]

Thanks Al. Quick question, my battery goes through a Perko switch. Will the voltage reading be correct at the battery?

[joe_db]

At the battery is what matters

[sastanley]

Bayou, AL's excellent post covers many scenarios. The problem is a lot of these boats now have seen multiple owners and many have changed things over the years, hence the need to figure out how your boat is wired.

If you were to measure the voltage at the battery, please take into account that ANY and ALL connections between the alternator and the battery could affect the ability to charge the battery, or limit that effectiveness. However, as Joe commented, that is the ultimate goal..make sure the alt brings up the battery when the engine is running. True battery voltage will be available at the battery posts, and should be somewhere between 12.6v and 12.8v at rest under no load. But, does it answer the question you are asking? The ammeter is likely in the middle of the circuit..your question is why does it read zero (or as I will explain later, appear to be zero?) I think the answer is at the alternator end of the circuit, not the battery end..for now. If you can get a voltmeter on the (+) output of the alternator and the (-) on a good ground on the engine (I use the alternator mounting bracket bolt, but mine is SS and not covered with paint) we can instantly tell if the alternator/regulator package is working. If it is not 13.8+ volts, one of those two is not working.
IMO, that is the first test, and then we move forward from there.

edit - to add in a few more thoughts, these older ammeters were WAY more range than ever could be put out by the 35A Motorola alternators. At first startup when you've drained the battery with the blower and the starter, you should see the gauge maybe as high as +15-20 amps for a minute or several minutes. As the battery is charged its ability to take those amps diminishes, it may be charging at 3 or 4 amps as it is being topped off, that will barely register on a -60/60+ ammeter. - There are MANY factors involved here, we are trying to figure out where your scenario falls and provide appropriate advice.

The next questions I have will be:
-What type of alternator?
-Original regulator?
-Wire gauge on alternator output?
-Does that output wire still run from the alternator to the ammeter in the cockpit?

[Bayou Sailor]

Thanks everyone for the input. This afternoon I will go to the boat and run these tests.

[Bayou Sailor]

OK, I tested the voltage at the battery and the alternator. When I got to the boat, the bat was at 13.8. Upon start up the voltage dropped to 12.7 and never got any higher. During the 15 min run time, it dropped down to 12.4. Checking at the alt, the readings never got over bat voltage. I think the alt is shot. I also think the gauge is shot because it never even ticks. Not even when you turn the ignition on or off. I just hate the thought of spending $250 for the most basic alternator made. I would think any 1 wire alt that fits should work. I am not a cruiser, only day sailor.