Alternator fun

[CHARLES FEARNEYHOUGH]

I was recently working on a 67 Dodge Dart Conv that I had installed a Holley Sniper on some time ago.
With the EFI, electric fuel pump, MSD, tunes, and modded headlights I also installed a 110 amp internally regulated alternator (and the required wiring to handle the additional load).
While working on spark delivery I managed to nail myself pretty good and, apparently, blow the regulator in my alternator. Luckily the EFI is still alive! After working on it I noticed 17 - 18 volts on the sniper display. Not wanting to shell out the 200 bucks for a new alternator I picked up a Mopar regulator from a local store and used it to supply the field voltage externally. This worked fine albeit the voltage seems a bit high for my liking hitting 15 sometimes but generally in the 14.2 to 14.6 range. Amperage draw on the field is running 5 to 6 amps which seems high to me as well. There is no AC coming from the alternator so I don't think the diode packs are damaged. Thinking that the issue might be the failed regulator I removed it, reassembled, and saw no change to field amperage draw. Found a replacement internal regulator on Summit and ordered it. Will see if that reduces field current and output voltage. Moving forward I think I'll stick to externally regulated alternators

 

[67Dart273]

A few ramblings:

The alternator may or may not have a damaged field, find the specs on the alternator and measure "full 12V" field current. 6A is not out of line, but I'd check just in case

USUALLY the reason V runs high is voltage drop TO the VR and this includes both the plus harness and the ground path. Check by doing this:

Turn key to "run" engine stopped. Measure between VR IGN terminal and battery PLUS post. You are hoping for a low reading, the lower the better. ANY reading there is ADDED to the VR set point as it ends up at the battery. That is if you measure .5V in this test, and if the VR is "wants to run" at 14.2, then the battery will see 14.8 IF the ground is perfect

Repeat this test with all accessories you can run, IE pumps, lights, etc

Now check the ground. Get engine to temp as the VR is temp sensitive. With battery "normalized" run this test first with minimal accessories, and again with all loads powered, heater, lights, etc

Stab one post into the battery NEG post and the other into the FLANGE of the VR. You are hoping for a very low reading, zero is perfect

If the battery is trunk mounted, run the ground test with the ground terminal as close to the batt as you can get, IE the grounding lead coming to the engine block, terminate to the engine block

For the pos. harness test, it would be best to get clear back to the battery. Just get a scrap piece of wire, no. 18 is fine, and connect to batt. pos and run up front to your meter, the other probe to VR IGN

 

[67Dart273]

I re-read you post. Where is the VR mounted? If it is not in the engine bay, temperature may be a problem. It may be that everything is actually OK if the VR is running at normal temps. 14.6 is not really abnormal.

Internal regulators are fine "if they are properly done." I do NOT care for "one wire" units but if an internal has a dedicated "sense" wire they should be fine.

 

[Dana67Dart]

Moving forward I think I'll stick to externally regulated alternators

Cant go wrong with 100 year old proved tech!

 

[CHARLES FEARNEYHOUGH]

I've made some significant changes to the lighting and ignition wiring on this vehicle. Both ignition wires and the low and high beam headlight circuits now feed interposing relays. The fused relay contacts are fed directly from the battery. This ensures that the EFI, MSD, and headlights are fed with the full voltage of the battery and not subject to the voltage drops that can occur at the bulkhead connectors and in the switches themselves. The regulator is also fed through this relay with its own fuse and is mounted in the original location in the engine bay. The alternator feeds back to the battery through a #4 conductor fused at 100A. The original alternator wire that goes to the ammeter is fused at 30 amps but carries very little current in the present configuration. When I pulled the alternator apart to remove the failed regulator there was no indication of damage to any of the windings. EE here, I spent my life working in heavy industry designing and troubleshooting control and power systems.

Oh, I went out and hooked up the original 35 amp alternator field to the battery. It draws 3.5 amps. So I'm guessing that the larger wire and magnetic field required to generate 110 amps on the armature might require 5 or so amps. I also imagine that the external regulator was never designed to provide field current for such a high capacity alternator.

 

[67Dart273]

"It depends". I think the Mopar 70/ later one, EG would do that just fine. Assuming it's not a cheapie Chinesioizationized one LOL

"Sometime in the 70's" (or early 80's) I was trying to fix a Delco 60 ish A unit from parts from cores. I ended up finally, "suspecting" and then proving to myself that YES I had one rotor with partially shorted windings. It drew lots of field current but would not output much. Only one conclusion, after having been installed in two different alternators --the rotor was partially shorted.

Yeh. Old--I'm 73. This was my 70 RR in either 73 or 74. This was a 440-6 car, Dana 3.54 and 18 spline gearbox, tracpac. Air grabber and black hood, tho you cannot see it here. When this photo was taken, it had a 340 swapped in!

 

[CHARLES FEARNEYHOUGH]

"It depends". I think the Mopar 70/ later one, EG would do that just fine. Assuming it's not a cheapie Chinesioizationized one LOL

"Sometime in the 70's" (or early 80's) I was trying to fix a Delco 60 ish A unit from parts from cores. I ended up finally, "suspecting" and then proving to myself that YES I had one rotor with partially shorted windings. It drew lots of field current but would not output much. Only one conclusion, after having been installed in two different alternators --the rotor was partially shorted.

Yeh. Old--I'm 73. This was my 70 RR in either 73 or 74. This was a 440-6 car, Dana 3.54 and 18 spline gearbox, tracpac. Air grabber and black hood, tho you cannot see it here. When this photo was taken, it had a 340 swapped in!

View attachment 1715818503

Very nice looking RR!

BTW I think you nailed it about the shorted field. Called Proform and was told this alternator should draw 2 amps on the field. Good call Obi Wan!

I'm headed to the garage to install the original 35 amp alternator until I pick up a new one. Thanks for your wisdom and your help.

 

[67Dart273]

You are welcome, I hope you are on the right road