what causes an alternator not charge?

[lime4x4]

I have a 1986 mecruiser 350 engine. I replaced the alt last year. This year the volt gauge is showing 10 volts less with a electrical load.I tested the voltage at the battery wire at the alternator and it was also showing 10 volts. I have power at the red and purple wire at the alternator. I was getting ready to just replace it then i decided to take it over to napa where i bought it and it tests fine and charges.Any ideas why it doesn't charge on the boat?

 

[Bigdaveaz]

Re: what causes an alternator not charge?

Have you load tested the battery?

 

[bjcsc]

Re: what causes an alternator not charge?

Have you load tested the battery?

Bingo!

 

[sarantis]

Re: what causes an alternator not charge?

What do you mean "This year the volt gauge is showing 10 volts less with a electrical load"?You count at the battery terminals 2-3 Volts?If so ,the battery is completely dead and so it can't get alternator's current.if you don't count on the terminals do it to check the voltage there.If you find it normal (more than 12V) suspect a bad ground or cable connection.Keep in mind that if a battery gives all its energy especially violently (by trying repeatedly to start a bad engine or from a bad starter)and is being left for some days empty it never reveals.What is your load?A starter causes more voltage drop than a lump.In anyway a voltage with load less than 11 Volts means dead or empty batery.Do you have it more than 4 years?You have also to check with the key of if there is a current leakage.

 

[lime4x4]

Re: what causes an alternator not charge?

i run 5 battaries. 1 to start the engine the other 4 or house batteries.I replaced all the batteries this year.Last year the volt gauge always shows 12 volts while idling and just over 13 volts when cruising. This year the gauge is showing just under 11 volts at idle and if i turn some lights on and the fridge while at cruising speed the volt gauge is reading below 10 volts.If i read voltage right at the output for the alternator it shows 9.9 volts now that's with a fairly heavy electrical load

 

[Uraijit]

Re: what causes an alternator not charge?

Sounds like you've got some bad wiring somewhere. Your voltage drop is caused by high resistance of the wires. Trace it out, and fix it pronto. High current through bad cables=fire...

 

[lime4x4]

Re: what causes an alternator not charge?

i'm alos reading the samething at the batteries as well

 

[Uraijit]

Re: what causes an alternator not charge?

Right, it's between the batteries, and the main load. Take the alternator wire, and disconnect it from the battery, I'll bet you get a normal reading out of the alt. It's just that the current draw is dropping the voltage of the whole system, and your poor alternator can't keep up. Fix it, or you'll be replacing a burned up alternator soon as well.

 

[Boatist]

Re: what causes an alternator not charge?

DO NOT take the alternator wire off the battery. If you do this it will blow the alternator in less than one second. The ouput diodes or regulator will blow in a fraction of a second with no load.

First step is to get the right service manual.

Does the the alternator have a external regulator?

How many wires are going to the alternator?
The big Heavy wire from alternator to the battery. Do you also have two smaller fires from the voltage regulator?

The Voltage before starting should be about 12.6 volts. After starting even at idle should be higher. At 1000 or more RPMS the voltage should be between 13.8 volts and 14.8 volts.

Are you charging all 5 batteries off the alternator. If you are then the voltage should be higher when you start the engine and when you increase the rpms but could take a long while before it gets near 14 volts.

Is the belt tight and near the top of the pulley? With the engine stopped is it hard to turn the alternator by hand?

My Guess is that you have an external voltage regulator and it is bad or the field wire is not connected.

 

[sarantis]

Re: what causes an alternator not charge?

i would keep only the one battery, the sterter's one ,and would check if it charges trying to isolate the problem.

 

[Coors]

Re: what causes an alternator not charge?

Right, it's between the batteries, and the main load. Take the alternator wire, and disconnect it from the battery, I'll bet you get a normal reading out of the alt. It's just that the current draw is dropping the voltage of the whole system, and your poor alternator can't keep up. Fix it, or you'll be replacing a burned up alternator soon as well.

Don't ever do that, it burns the diodes.

 

[Don S]

Re: what causes an alternator not charge?

Uraijit

No, ur

 

[Coors]

Re: what causes an alternator not charge?

Uraijit

No, ur

That's like your isp, or keyboard locked up, Don.
All ok?

 

[Coors]

Re: what causes an alternator not charge?

I'm gonna be a post- ***** and bump this one.

 

[Coors]

Re: what causes an alternator not charge?

bump

 

[lime4x4]

Re: what causes an alternator not charge?

i'm going to reinstall the alt and hook the output wire directly to the battery and c what happens

 

[Bigdaveaz]

Re: what causes an alternator not charge?

I have a 1986 mecruiser 350 engine. I replaced the alt last year. This year the volt gauge is showing 10 volts less with a electrical load.I tested the voltage at the battery wire at the alternator and it was also showing 10 volts. I have power at the red and purple wire at the alternator. I was getting ready to just replace it then i decided to take it over to napa where i bought it and it tests fine and charges.Any ideas why it doesn't charge on the boat?

What causes an alternator not charge?....... It/s broke!

 

[Uraijit]

Re: what causes an alternator not charge?

Don't ever do that, it burns the diodes.

You're right. I didn't type out what I was trying to say. I meant to disconnect the alternator from the main load, and see how it charged a battery on its own. My bad :redface:

 

[lime4x4]

Re: what causes an alternator not charge?

well i reinstalled the alternator and hooked up the output wire directly to the battery and it's charging. I still have the original output wire hooked up to the starter and that shows 14.3 volts. I'm just going to keep it hooked up directly to battery for now and c what happens

 

[Don S]

Re: what causes an alternator not charge?

What do you mean you are going to leave the original wire hooked up and see what happens. It's supposed to be hooked up, or nothing will happen. (except you loose the alternator diods again)