Alternator and charging issue.

[ben_2_go]

I had to jump start my '01 Ranger,and it fried the diode.I took the truck to my local auto parts house and had it checked.It checked out as low charging 13.5v and bad diode.The battery was charged and checked out in the high range of good.So, I replaced the voltage regulator in the alternator.Now I have no voltage loss when the truck is off.When I start the truck,my multimeter shows that it is charging at 14.2v.When I turn on the lights and heater blower,it drops to 13.5v.When I shut everything off,it remains at 13.5v.Running the engine up to 2000rpm doesn't make a difference.It holds at 13.5v.I checked my cables and they are fine.No rubs or bare places.The cable battery clamps are clean as well as the battery posts.Should I replace the alternator or is there something else I should check?

 

[ben_2_go]

Update!

I let the truck sit over night and most of the day.I drove my car instead.I checked the resting voltage of the battery and it was down to 11.5v.Luckily,the truck started, but barely.

I checked the idle voltage and it was up to 14.1 to 14.2.I drove the truck around a few miles to do some errands.I had the alternator and battery checked again at a local parts store.The voltage for them was 14.1 and the battery resting voltage was 12.58,but the cold cranking amps was only 280.

So,I drove the truck around a little more,and rechecked the battery resting voltage at 12.8v and falling.I checked idle voltage and it's up to 14.6v.After the alternator and battery gets warm the voltage rolls off to 14.2v.I think that the brushes in the new regulator need to be run in, so they make better contact with the stator rings,and the battery needs to be replaced.Oh,the diode checked out,so it's a battery issue now.

 

[RonD]

When you start any vehicle the voltage regulator will turn up voltage to above 14volts.
That is called "recharging" voltage, usually +2 volts above battery "at rest" voltage
After a few minutes the voltage regulator will start lowering the voltage to 13.5/13.6volts
That is called "Maintenance" voltage, usually 1.1volts above at rest voltage

So what you describe is normal operation

If you send a 12.5volt battery 14.5volts for more than 10 minutes the battery fluid will start to evaporate, this will shorten the life of the battery.
You need the "fast" recharge because that is better for a vehicle battery, thin plates, but it needs to end fairly fast as well..

Unhook one battery cable and test battery voltage, say it is 12.5volts
leave cable unhooked and test it again the next morning, should still be 12.5volts
If it is lower then battery has internal short, plate set is shorted, so battery is self draining.

If voltage is the same then do the same test but leave battery connected to vehicle.
If voltage is lower then you have a vehicle circuit that is draining the battery.

 

[ben_2_go]