Recently my voltage has been low after the truck sits overnight or for longer than 10-12 hours. When I go to restart the truck it usually sits around 10-11volts. Sometimes the alternator will kick in and the voltage goes up to 13.6ish. Other times the alternator will not turn on until I rev the engine over 2500rpm. Then I'll hear the alternator whine interference noise through the speakers. Once it starts charging, it stays fine until the truck sits for a while.

I've narrowed the drain down to the alternator by removing all fuses and reading 12.6v from the negative post on the battery to the body while the positive wire is connected to the + post on the battery. When I remove the wire that goes to the alternator the voltage disappears.

The alternator is an aftermarket 6g 200amp from alternatorparts.com. This is my 2nd one from them as the 1st one took a dump less than a year after I purchased it. I do have a 1000w RMS stereo (that rarely gets used to it's full potential) and other minor electrical add ons but they are also rarely used.

From my research on the net and here, I'm leaning towards the diodes or voltage rectifier. I'd like to open up the alternator and fix it myself if possible.

Any help is greatly appreciated!

 

Go ahead and open it up. The diodes should show around .7 volts in one direction and open in the opposite direction. The diodes are the rectifiers that is what they do. They rectify the voltage from AC to DC. It is the voltage regulator in these that I have not ever messed with so I cannot help you there.

 

I would suggest you do a parasitic draw test. we are looking for no more then .50ma (imo.50ma is still to high but that is spec) after the modules go in to sleep mode.

 

also a poor mans test for a diode is to check the batteries for a/c voltage when its charging. more then a few tenths its an issue

 

You mean 50 milliamps?


It takes a while to go into sleep mode --- and meanwhile, it can spike up to 300 milliamps.

 

Do a reset of the computers.

Disconnect your high tech stuff --- stereo etc. to eliminate that as a cause.

 

yes sorry, thanks for the correction

 

That is a good test that just about any dvm will work on.

 

I was very surpised to find a dc battery could infact store some amounts of ac voltage.

 

That is interesting, it must store only the positive half of the cycle.

 

Do you know that for a fact or could it be helping in the deteriozation of the batteries??

 

I would not think that the negative half cycle of an AC sine wave would do a DC battery any good, except to discharge it.

 

that is fact that it will. I dont know what ill effects it really has on a battery. I test for it only with the engine running. I know a/c voltage plays havoc with eletronics that should not have them.

 

So just stick the leads of the DMM on the battery posts while the truck is running and the alt. is charging and check for AC voltage? I'll give that a shot in the morning.

Oh and I forgot to add that I had both batteries charged and tested. Both tested good and are less than a year old.

 

you got it. more then about .2-.3 suspect diodes. postthe test results too please.