Batteries 100% drained dead - new problem

[Old Goat]

Install a Vacuum Gauge, these truck should all have one.
I have a Stewart Warner Gauge to see where the Vac is.
Also have a SW Volt Gauge. That stupid Amp Gauge is just
to take up room in the Instrument Cluster, never did move.

Volt Gauge is installed where the Tack is suppose to live.
And Vac Gauge is moved from there to the place the GP
Start light lives. Should fit.

Goat

 

[RSchanz]

Ok, wen't a bit in the other direction and just ordered a new voltage regulator. I'm not too interested in going picking at the junkyard to find the stuff for the 3G swap. Regulator is $40 on summit racing and I can try that first. Just going to focus on attempting that and then replacing the ground and positive cables with some nice fresh ones. Will report back! Thank you for all of your help and input in solving this problem.

 

[IDIBRONCO]

Hopefully, this takes care of your problem.

 

[RSchanz]

Put the new regulator on, started the truck and the multimeter read 13.65(ish) when running and then when accelerating it only got up to like 13.85. I will say, that after shutting off the truck and checking the battery again the batteries went from 12.52 up to 12.84 so it seems like it did charge the battery a little.

 

[IDIBRONCO]

Your alternator will charge the batteries at that output, but not very quickly. I think that it's likely that your alternator is also weak.

 

[BeastMaster]

If your batteries need charging, they may be pulling the terminal voltages lower until they charge back up.

The big question...did your sneak current path go away?

The batteries look like they are charging...I'd just put the truck back into service and see if the batteries charge back up.

Keep an eye on it though. Shorted turns in the alternator armature can damage voltage regulators in a manner consistent with your experience. But alternators are much more expensive and I hate to replace them without proof they are bad.

However, as IDIbronco pointed out, if the output looks weak, there's your root problem. With age, contaminant intrusion, and thermal cycling, winding insulation can fail. Usually as shorted turns.

Most of my experience is derived from an old gasser I used to own. Anyone here know whether the armature terminal is grounded, or connected to batt+ to drive the alternator to full output?

 

[DaveBen]

The armature is the source of power so it is connected to the + of the battery.

 

[RSchanz]

I did the same test with the test light after replacing the regulator and the draw seemed to disappear.

Yeah, I'll probably just drive it around town and see how it does. At the moment the truck is used for longer trips with a camper on it so not ideal to just wing it haha.

Why is the armature question relevant?

 

[DrCharles]

The armature is the source of power so it is connected to the + of the battery.

Not quite. It's "backwards" from what you might expect...

The rotating armature on an alternator is actually the field winding, and the current to the armature is what determines the available output current. So it's connected through the two brushes and slip rings to ground and to the voltage regulator.

The stator is where the power comes from, and it's a three-phase winding connected to a hefty rectifier bridge...

 

[BeastMaster]

Very happy to hear the short went away. That's positive confirmation the leak path was through the voltage regulator failing to shut down alternator armature current when the truck is supposedly OFF.

I brought the armature winding short concern up because shorted turns in the alternator windings will cause the voltage regulator to "drive the hell out of" the armature current trying to get the alternator stator output voltage up to setpoint ( approx 14 volts ).

Such sustained drive can stress the current pass transistor in the regulator to such a point the transistor fails ( usually an internal "emitter to collector" short ).

However, these things are designed for automotive use and should be designed for this event.

I was considering your woe fits a pass transistor failing shorted.

Being internally shorted, it failed to turn completely OFF when you shut the truck down...hence your current leak when everything is supposed to be OFF. The current draw, as shown by the brightness of your test lamp, was indicative of a pretty hefty load. Your alternator's armature winding fits that observation.

Keep us informed as to if this fixed it or it ain't done yet. A lot of us will learn from this.

 

[RSchanz]

I see. At the moment the batteries have been attached to the truck for probably 36-48 hrs and remain at 12.56 so I’m fairly certain the parasitic draw has been eliminated. The truck hasn’t been driven yet though so I’ll report back after that.

I might replace the alternator or research local rebuild options just to update it. I’d love to keep the motorcraft alternator if possible.

I found this video helpful for diagnosing alternator issues and at one point he says "heat is an enemy for alternators" and considering how hot these engines are already running plus that I was driving during 110 degree heat plus residual heat from the asphalt I'm wondering if it did in fact damage the alternator as well. Still need to run these tests ASAP.

xc_hide_links_from_guests_guests_error_hide_media

 

[BeastMaster]

Nice video.

The only bone I have to pick with it is about what he called the field connection, which I was calling armature current. That is how the voltage regulator controls the alternator output. I've seen this in two configurations: pull it to +12 volts, or pull it to ground, to put full power to the armature. In operation, the regulator watches the battery during run to hold the battery voltage at 14 volts or so, using the field ( armature current ) as the feedback control.

So, it's gonna vary, depending on how much juice you need to maintain 14 volts on the battery rail.

Your alternator uses more advanced technology which also sends a sample of one phase of the stator voltage to the regulator.

There are auto shops that specialize in electrical stuff that can thoroughly check out your alternator in minutes, in place, with a test load and an oscilloscope. What their test load will do is put max load on the alternator, and they will simultaneously verify all three phases of the alternator stator windings and all diodes. Any shorted windings or bad diodes will show up on the oscilloscope display. They know exactly what to look for, and getting their approval of your alternator status may give you some peace of mind before a road trip.

I hate to advise you to change out expensive parts when I know the technology is out there to quickly and inexpensively diagnose alternators... you don't even have to remove it from the truck. ( It needs the truck to spin it during the test anyway ). They know what all the currents and voltages should be and give you wise counsel.

But I would advise you to seek counsel on a possible bad diode in the three phase bridge. This is indicated by your lower than expected alternator output voltage.

I found another video you may find helpful:

xc_hide_links_from_guests_guests_error_hide_media

 

[lotzagoodstuff]

I might replace the alternator or research local rebuild options just to update it. I’d love to keep the motorcraft alternator if possible.

+1 on getting it rebuilt locally, you just have to find the best guy in your zip code. If you were in Seattle this would be very easy: Scott at "The Rebuilder" on Central is the absolute best I've ever met. Too bad he's not closer to you.

 

[lotzagoodstuff]

Just in case you can't find anybody local, this is from the "Those Who Provide Excellent Service" sticky:

If you are looking for a starter or alternator rebuilder in the greater Seattle area, look no further. Scott is "The Man". Super knowledgeable, super detailed, super fast and get this: competitively priced. He's got a ten second first gen Mercury Cougar too

My PSD and IDI both have rebuilt products from Scott and I would call his customer service "premier".

The Rebuilder
722 Central Avenue South
Kent, WA 98032
(253) 854-0904

 

[BeastMaster]

There definitely is an art to rebuilding. I tried to rebuild mine after my glow plug disaster. All I did was make a fried alternator completely destroyed beyond all hope of repair. But at least I met the bear that got the better of me.