troubleshoot alternator

[Jeffreyi]

How can I check my alternator to be sure it's charging battery, etc.?

 

[NYBo]

Re: troubleshoot alternator

You can get a rough idea with a voltmeter. Do you have room to install one in the instrument panel? If not, hook one up temporarily and run the motor. You should get a voltage reading of 13.5 to 14.5 volts at the battery if the alternator is working.

 

[wire2]

Re: troubleshoot alternator

After 10-15 minutes of running, put your hand on the alternator. If it's cold, it's not producing. Warm is good.

 

[bruceb58]

Re: troubleshoot alternator

After 10-15 minutes of running, put your hand on the alternator. If it's cold, it's not producing. Warm is good.

What if its warm and the voltage is only 12.8V. Still think its good? What if the diodes are thrashed and its putting out a bunch of AC. Still think its good?

Need to measure it with a voltmeter. Only way to determine it is good.

 

[wire2]

Re: troubleshoot alternator

What if its warm and the voltage is only 12.8V. Still think its good? What if the diodes are thrashed and its putting out a bunch of AC. Still think its good?

Need to measure it with a voltmeter. Only way to determine it is good.

12.8v will not be producing noticeable current and will not cause heating in the windings. Open diodes will also not pass current.

I was offering an indication of a *probably* working alternater. Obviously it's not a positive test, like with a voltmeter.
But I doubt that even 50% of boaters own a voltmeter,
and even fewer know how to use it.

 

[dockwrecker]

Re: troubleshoot alternator

^-1 Now now that's a bit harsh. People have volt meters, but agreed, they may not know what to look for. The advice to look for 12.5-14.7 volts off (above) idle at the battery is good, weak readings would suggest taking it to a proper rebuilder for additional load testing. Marine alternators are spendy new and can be rebuilt by a competent shop relatively cheap with good results. Any basic voltmeter will do.

 

[bruceb58]

Re: troubleshoot alternator

I was offering an indication of a *probably* working alternater. Obviously it's not a positive test, like with a voltmeter.
But I doubt that even 50% of boaters own a voltmeter,
and even fewer know how to use it.

His question was how to check his alternator. Feeling it to see if it is warm is pretty worthless.

By the way, diodes can also fail short.

 

[Jeffreyi]

Re: troubleshoot alternator

I charged the battery all day but it only got to 12.8 v as per my charger. I tried to start it but it just cranked slowly with no start. The positive post/wire on the battery was very hot to the touch. Is this normal?

Thanks.

 

[kmarine]

Re: troubleshoot alternator

I suggest to try a load test on your battery. I purchased a load tester on line for about $20. They also have the ability to check the output voltage of your alternator. Works on any type of vheicle and pinpoints battery or alternator issues.

 

[stylesabu]

Re: troubleshoot alternator

I charged the battery all day but it only got to 12.8 v as per my charger. I tried to start it but it just cranked slowly with no start. The positive post/wire on the battery was very hot to the touch. Is this normal?
heat means resistance. poor connection most likey, bad starter

 

[Don S]

Re: troubleshoot alternator

The positive post/wire on the battery was very hot to the touch. Is this normal?

No, it's not normal. Loose or corroded terminals cause heat. Clean and tighten the connections and get rid of the wing nuts, use real nuts and a wrench to tighten the connections.