Electrical help wanted

[dino7]

I had some battery trouble earlier this spring, which I chalked up to a battery that simply need replaced from 2 years of use, and alot of time sitting with the radio on, ballast pumps running, etc. So I got a new one about 4 weeks ago, and today after about 3 hours I started getting a low voltage alarm. The voltage was showing as 11.5-11.6 volts. We kept the boat out for another hour or so, not turning it off at all. The entire time the voltage never read higher than 11.6. Typically it reads 14.2 V while running, which I assume is the output voltage of the alternator. I should include that since I have replaced the battery, I have not run any pumps when the boat was not running, and have hooked the battery up to a drip charger about every 5-7 days. Is this a failed alternator, or is there something else it could be?

thanks for your help

[MalibuTime]

I had some battery trouble earlier this spring, which I chalked up to a battery that simply need replaced from 2 years of use, and alot of time sitting with the radio on, ballast pumps running, etc. So I got a new one about 4 weeks ago, and today after about 3 hours I started getting a low voltage alarm. The voltage was showing as 11.5-11.6 volts. We kept the boat out for another hour or so, not turning it off at all. The entire time the voltage never read higher than 11.6. Typically it reads 14.2 V while running, which I assume is the output voltage of the alternator. I should include that since I have replaced the battery, I have not run any pumps when the boat was not running, and have hooked the battery up to a drip charger about every 5-7 days. Is this a failed alternator, or is there something else it could be?

thanks for your help

You are on the right track. Probably one or more of the following:

Alternator is failing

Belts are not tight enough to properly drive the alternator, but often you should hear the telltale squeal of slipping belts

Electrical connections are not cleaned/grounded - start at the battery and check/clean major terminals throughout

Possible, but seems like you would know if you had something in the system malfunctioning and drawing massive load

[Sunsetter95]

I had some battery trouble earlier this spring, which I chalked up to a battery that simply need replaced from 2 years of use, and alot of time sitting with the radio on, ballast pumps running, etc. So I got a new one about 4 weeks ago, and today after about 3 hours I started getting a low voltage alarm. The voltage was showing as 11.5-11.6 volts. We kept the boat out for another hour or so, not turning it off at all. The entire time the voltage never read higher than 11.6. Typically it reads 14.2 V while running, which I assume is the output voltage of the alternator. I should include that since I have replaced the battery, I have not run any pumps when the boat was not running, and have hooked the battery up to a drip charger about every 5-7 days. Is this a failed alternator, or is there something else it could be?

thanks for your help

You are on the right track. Probably one or more of the following:

Alternator is failing

Belts are not tight enough to properly drive the alternator, but often you should hear the telltale squeal of slipping belts

Electrical connections are not cleaned/grounded - start at the battery and check/clean major terminals throughout

Possible, but seems like you would know if you had something in the system malfunctioning and drawing massive load

That includes the ground connections. Neg cable at the engine could have some corrosion or rust under the cable connection. Some alternators have a ground on the alternator case also.

Edited June 14, 2009 by Sunsetter95

[scfdfireman]

If your battery shows 14+ volts (at the battery) when its running then it seems that your charging system is working OK. Check for sources that drain the battery, stereo, amps, lights, bilge pumps, sac pumps, engine computer, etc and have a volt meter on the battery at the same time. Hopefully when you disconnect the correct source of the power drain the battery voltage will go up a bit. Be patient, it will take a while to find the culprit and it could be as simple as a bilge or sac pump that's frozen (so it's quiet) but still draining power.

[dino7]

The voltage was generally reading 14.2 when running until sometime this morning. Next thing I know I'm getting a low voltage alarm and it was at 11.5V. I always assumed that alternators failed catastrophically. Is it possible for one to work intermittently before failing completely? I did also check the belt, and it seemed tight.

If your battery shows 14+ volts (at the battery) when its running then it seems that your charging system is working OK. Check for sources that drain the battery, stereo, amps, lights, bilge pumps, sac pumps, engine computer, etc and have a volt meter on the battery at the same time. Hopefully when you disconnect the correct source of the power drain the battery voltage will go up a bit. Be patient, it will take a while to find the culprit and it could be as simple as a bilge or sac pump that's frozen (so it's quiet) but still draining power.

[scfdfireman]

How it fails depends on what died or is dying. If it's the brushes inside the alternator it may work at times depending if they make contact, however, if it's the diodes then they usually fail and that's it. It sounds like you found your problem, either rebuild it or replace it.