Alternator problem/dead batteries....
 

Baja 272, 502Mag EFI

Went out on the boat twice (sorry cold weatherers) this weekend, beautiful sunny days, no problems running real hard on Sat, a minor hiccup with the family on Sunday. Got back to the ramp, pulled the boat,wanted to flush, turn the key, "click", no starter, dead betteries.

Pulled out my camping backup battery to complete flushing and it worked, nice clean engine sitting there.

Since about 2 months ago, my voltmeter has been on a downward slide. Started at 11.5 with blower on, now is down to below 10 without the blower, looks like about 8 with the blower .

First question, what does the voltmeter read? The output of the alternator, or the current battery charge status? If it is the batteries, weird, because I charged both of them last week, but interesting enough, neither would take a full charge, stopped midway on both. So maybe the batteries are old and have to be replaced ( boat bought in March with existing batteries).

However, if the alternator is bad, and the boat needs juice from the batteries to operate, this could be a symptom too. One more note, seemed to get a short multibeeping alarm at startup before the dead battery try at the ramp. My inclination is to buy two new batteries, but don't want to if it is a bad alternator. The alternator looks nice and new, but who knows. Could it be wiring or salt corrosion (I boat only in ocean salt)?

Can anybody give me ideas? Thanks in advance.

Chris

Re: Alternator problem/dead batteries....
 

If the alt is working it should show 12V or better when running. Your batteries should show 12V with just the key on. It sounds like you are the proud owner of two bad bats and a alt.

Re: Alternator problem/dead batteries....
 

Doesn't the voltmeter indicate alternator output, and not the voltage of the batteries?

Re: Alternator problem/dead batteries....
 

There all on the same circuit, the gauge doesn't isolate a reading from one or the other. With the key on it's only going to show you the reading from the battery. With the motor running it's going to show you what the alternator is charging plus or minus what the charge of the batteries are. So for instance you should be charging somewhere in the 13.5 range but if your battery is at 8 volts your gauge may read somewhere in between. Pull you alt and your batteries and go have them all load tested, or start with your batteries(if that's easier) have them tested first. If they are fine than you need to have your alt tested. Remember your marine alt is probably a 55 or 60 amp unit. They have a tough time charging two dead batteries unless your doing lots of running. One more thing I would check while your in there is to make sure you have good connections for your ground (usually on the bell housing) and your positive (on the starter) along with the battery terminals. Any one of those could be a bad connection and keep you from charging properly.

Re: Alternator problem/dead batteries....
 

Charge the batteries first and have them tested... The only true way to test a battery is to fully charge it and then test it for 10 seconds at 50 percent of it's cold cranking ampherage. If the battery is a 550 cold cranking battery, you put a load of 275 amps on the battery and watch the voltage drop... It shouldn't drop below 9.6 volts. 10 is ideal. You cannot test a battery in that manner with a cheap tester.. you have to have a big tester with a carbon pile to load it that much. Most automotive repair centers should have one... I have one.. Then when the battery is tested... you start the engine and test the alternator. The voltage under load should be 13 to 13.5 volts and the output can be tested by loading the charging system and watching the amperage rise on the meter. Again... it has to be a decent tester.

The very first thing you should do is clean the battery terminals then charge your batteries. I have had bad battery readings thinking it was the battery or even the alternator but when I cleaned the terminals, the voltmeter read 13.2V before and after start up.