Low Voltage

[jimkov]

Hello,

Problem: Low Voltage on 1970 Dodge Challenger
Voltage output shows 10.6 Volts at the alternator when running and battery shows11.5-11.7 Volts

Engine: 383
Battery: Oddessy Xtreme
Alternator: New Tuff Stuff 8509RCDP
Car has Edelbrock Serpentine belt and electic fan

I have replaced the Voltage regulator with a Chrysler model with not change. I have also reran new ground wires to the battery and alt with no changes. I checked the short wire from the voltage regulator to the block and it looks good. I bypassed the ammeter by putting both wires on the same pin and also ran a line directly from the starter relay to the alt as a test and there was no change.


Any idea on what else I could try? There is no change is voltage if I let the engine idle or rev it to higher rpms.

 

[72RoadRunnerGTX]

Sounds like a full field test is the next order of business. Remove the green field wire from the alternator and ground the terminal, see what the resulting output voltage is. Be sure there is battery voltage present on the other field terminal (blue wire).
Be really careful with those mentioned by-passes in place, there will be little to no circuit protection in the event of a short in the stock charge path.

 

[jimkov]

No change to the output when grounding the green field wire. Still reading 11.6V.

 

[72RoadRunnerGTX]

What do you have on the other field terminal (blue wire)?

 

[jimkov]

10.0V on one and 0.3 to 1.2V on the other. I forget which color was which reading. I can check again tomorrow.

 

[jimkov]

Charged it overnight on the trickle charger and it was at 12.8V. Started it up and got 12.0 V at the alt and the battery at 12.0 V. Idling at about 1000 rpm and not change woth higher rpms.

 

[72RoadRunnerGTX]

Did you perform a full field test? Disconnect the green field wire from the alternator and ground the terminal, make sure there is battery voltage on the blue field wire with the key on, is there higher than battery voltage at the alternator output stud while running with a full 12 volts applied to the field terminals?

 

[jimkov]

No they are both reading 11.9V at the blue and positive terminal on the alt.

 

[72RoadRunnerGTX]

With the other field terminal grounded? Alternator is bad.

 

[jimkov]

Yes, with the terminal grounded. I tested the wire to the voltage regulator and it's good. So I used a press to pull and install the serpentine pulley. I was a careful as I could be but is there a anything I could check that I might have damaged and fix on the alt? It's a nice Tuff Stuff alternator so I bet they have a good QA/QC and I did something to it.

 

[jimkov]

I also have a brown wire connected to the blue field terminal, could that be the issue. I am not sure where that

wire leads.

 

[72RoadRunnerGTX]

Yes, Tuff Stuff is good, run them as well. You’ve had it apart then? Once more, you removed the green field wire and grounded the terminal to the alternator case? Disconnect both field wires, check for continuity between the two field terminals. Make sure there is no continuity between either terminals and the alternator case. Ensure the insulated brushes are assembled correctly and they in contact with the slip rings on the rotor.

BTW, you should insulate those two female Packard field connectors. No fuse protection on the blue ignition 1 wire, will burn wires if grounded while the key is on.

 

[jimkov]

This looks off. Looks like a field wire connector shorted out and also looks like I might be missing that push rod that makes contact with the shaft. Should I have another one if those black pins on both?

 

[72RoadRunnerGTX]

The brush assemblies have to be removed before disassembling and/or reassembling the case halves, you will need new brushes. Looks like you reassembled it with the brushes in place, are now damaged, needing replacement.

 

[jimkov]

Thank you for the help!

 

[72RoadRunnerGTX]

You bet. You will want to clean out the remnants if that missing brush from anywhere near the bearing before reassembly.

 

[jimkov]

That worked. I ended up removing the brush and putting it back one after I put the two halves of the alternator back together. The regulator did start working. I got a Chrysler voltage regulator but ended up putting the Chinese one back on. For whatever reason the Chrysler maxes out at 13.2V when I rev the engine and the Chinese version peaks at 14.5V.