Do I Need A New Alternator?
 

Over the weekend I noticed when i was trimming up the radio would shut off? then come back on? then noticed my volt gauge read 11.5v-12v while under way . When I got home I put a volt meter on the battery while running and it read 12.4 volts, is this to low? my first thought was was bad ground?

Re: Do I Need A New Alternator?
 

I'm no mechanic but if you put a meter on the battery while motor is running you'll get a pretty good idea if its the altenator. should be 14 atleat, motor off your checking the battery, 12.4 is low.

Re: Do I Need A New Alternator?
 

motor off was 11.8, motor on was 12.4? i thought that was low also, could it be anything else?

Re: Do I Need A New Alternator?
 

should be aprox 13.8 running

Re: Do I Need A New Alternator?
 

Full charged battery is 12.7 Depends on your volt meter as to what you see. Take your volt meter & put on your car/truck. Running voltage should be aprox. 13.8 volts, sometimes it will be higher & sometime lower. This will give you a good idea of what your meter is readiing. I would say your alt. needs to be replaced if the numbers you are giving is correct. Before you buy a new one have the one you have checked out first. Could also be a ground problem.

Re: Do I Need A New Alternator?
 

Could very likely be a bad battery. Alternators should produce about 13.8 volts under normal conditions however if the batery is sucking up current (amps) flow (voltage) will decrease. You can't make alot of current and maintain voltage at the same time, the higher the voltage reading is the more charge the battery has in it. Although the bit about the stereo cutting out during trim operation points to an alternator. It's just a little odd becuase your alternatot is producing some power which is evident by the increased voltage while running. Ussualy when an alternator fails it fails completley and does nothing, but not always. Take em both out and have em tested.

Re: Do I Need A New Alternator?
 

The way I used to check to see if I had a bad alternator was disconnect the battery while the boat was running and if it died that meant the alternator was bad. If it kept running alternator was good. But I also heard not to do that on computerized engines.

Re: Do I Need A New Alternator?
 

I had the same problem and it was a bad battery. I was running two batteries and the good one covered at normal loads but the trim and radio would kill both of them.

Re: Do I Need A New Alternator?
 

I would 1st try the simplest: pull the battery out and do a full load check on the battery, along with a volt check by cell if a non-sealed unit and voltage drop test on grounds and positive leads.

If battery has failed, install new and retest charging system output.

Re: Do I Need A New Alternator?
 

Mine does the exact same thing.
I've got a new battery and all. Did it with the old battery too. I've cleaned all the connections and it still charges at 12V or less.
I'll pull it this winter and have a local rebuild shop look at it.

Re: Do I Need A New Alternator?
 

replaced alternator last week....charging @ 13.8....problem solved...thanks for all your help.

Re: Do I Need A New Alternator?
 

Good deal!!! :drink:

Re: Do I Need A New Alternator?
 

I also have the same problem, charging at less than 12V. However, I've steered away from the problem being alternator-related since both engines/gauges read low, exactly, at the same time. It is not logical to think both alternators are equally faulty.

Am I not correct here? Would one bad alternator make both engines/gauges charge and read low?

I've been chasing other common points between the two engines such as dash connections, engine connections, battery switch, etc. Actually, I just replaced the battery switch because it was so hard to turn, really grinding away inside the switch. I'm hoping maybe the switch was partially shorting out. Haven't checked it though, she's laid up for the winter now. :(

Re: Do I Need A New Alternator?
 

I had same symptoms this year and it was batteries. When I checked the date code they were 6 years old! They were due to be replaced. Third, your problem is you need to trade old ironsides for a clean '99 Donzi 28zx brother! The SBCs will fit into your miserly running style and you'll look alot better when ya finally do catch up!

Re: Do I Need A New Alternator?
 

I wouldnt disconnect any alternator to check voltage especially a marine alternator.Taking the lead off causes the alt to spike and you will definately cook it!

Re: Do I Need A New Alternator?
 

Turn the battery switch off while the motor is running....if it shuts off it's a good indication you have a problem with your alternator.