Retest the new batteries, one of them maybe faulty.

Retest the alternator after you know both batteries are ok.

Check the FICM after your charging system is working again, should read 47-49v range.

Could also be a bad battery cable too.

Harry

 

i have a slow drain on my batteries also, just not as bad as yours.
i think my GPS unit and amps are slowly taking my juice.

 

I agree with Harry. I would also do a voltage drop test on both positive and both negative cables. You may have a bad ground.

 

Voltage drop test is a good idea, also when you shut it off take a wrench and put it flat onto the pulley, some alternators will not turn off the power to the commutator.
Just a thought!

 

Can you explain what you mean by putting a wrench flat onto the pulley?
This sounds like your saying short something...sorry, not clear to me what you mean.

 

John means to see if a wrench is magnetically attracted to the alternator pulley. Also try this to the back of the case too. If so, there is current flowing through the commutator windings which should not be when the engine is shut down.

 

Ok just tested the batteries and alt.

with the truck off im getting 12.1 at passenger side battery, 12.1 at driver side battery and 12.1 at the alternaor.

With truck idling passenger side drops to 11.9, driver side drops to 11.8 and alternator at 11.9.

SCT still reads about 11.6.

 

Doesn't sound as if the charging system is working. The drop in voltage is most likely the electrical draw of the engine components to allow it to run. The voltage drop split being even is a good indicator that the source is suspect. That charge voltage should be up around 14.2 vdc at a minimum when the engine is running.

 

:whs

The alternator sounds bad. Where did it come from? Mine is around 14 volts once the glow plugs stop cycling.

 

You need 13.8 volts at the batterys to fully charge the battery, after a maximum of 5 minutes the voltage should be at least 13.8 volts, 14.2 is much better, especially if the unit is driven on short trips.
Backslap is correct about the wrench, I would not do it at the back of the alternator.
I would take it to the shop you got the alternator from if the voltage drop tests all check out. A maximum of .2 volts on the power and ground side.
Just a thought!

 

OK. Makes sense...I wonder who found this out by accident?

 

That trick with a wrench of piece of ferrous metal has been performed for many years to test for current flow through the rotor windings when if shouldn't be there.

One thing that needs clarified is that alternators do not use commutation, (commutator) segments as does a starter motor. Commutators are used in DC applications and are very good at both generating clean DC voltage and current, and consuming the same. Modern alternators use slip rings to pass field excitation current, (voltage) to the rotor inducing an alternating current, (AC voltage) into the secondary stator windings. This AC voltage is then rectified by the diodes of the alternator to produce DC voltage and current to operate the electrical system in the vehicle.

The wrench trick mentioned doesn't really matter at the front or rear of the alternator case. Most electrical connections are at the rear and I'm certain this is why John mentions he wouldn't use the rear of the case. In actuality, it is the same point electrically but you stand a greater chance of shorting something electrically at the rear rather than the drive sheave, (pulley). If you have magnetism in the alternator rotor when the ignition is shut off, there is field excitation current flowing through the rotor windings that is not being disconnected by the ignition circuit relay, or a shorted internal winding within the alternator itself. There should be no magnetism present other than residual which would not be enough to attract a piece of metal.

 

Question, is this a single or dual alternator setup? And have you checked for voltage at the battery terminal at the alternator(s)? You may have a fuse link out. Also on a voltage drop I want less than 0.1 volts.

 

Single alt set up.

Can you explain how to check for voltage at the battery terminal at the alternator?

 

On the back of the alternator you have a terminal that is a larger wire that should always have battery voltage. If it does not have battery voltage, you have a bad connection or bad fuse link.