High Voltage

-
Unprovoked

Unprovoked

Member
Joined
Jan 8, 2009
Messages
21
Reaction score
0
Location
Chicago, IL
Hey guys,

I'm having a problem (we'll I've had a few problems) while fixing some wiring that burned up on my 73 Duster w/ 318.

Initially, I did the MAD electrical ammeter bypass, replaced all the wiring on my alternator, bought a new voltage regulator and a new 78 Amp alternator. Once I got the car fired up, the voltage was fluctuating a lot. I put the old regulator back in and voltage stayed steady at 13v, but I would blow a 40A fuse I had installed in place of the fusible link on the alternator battery cable when I would rev the engine above idle. I looked around for shorts, but found none, so I took the alternator in to get tested and it tested bad. So I installed a new alternator (again) and a new voltage regulator (again) and now the voltage at the battery won't come down from 15.6v. I thought maybe it was just because it was a little cold out and the regulator is temperature compensated so I let it warm up, but voltage didn't drop. I thought maybe it wasn't grounded enough, so I added a ground directly back to the battery, still no drop in voltage.

Any thoughts on what I else would make voltage stay so high? Should I just try a different part stores voltage regulator? Any ideas are much appreciated!!!
 
1) Measure the voltage at the +12v wiring going into the VR (normally blue) and see if it is close to the voltage at the battery. If not, then it is a wiring or voltage drop issue to the VR that needs to be fixed.
2) If it is good then, remove the green filed wire from the back of the alterantor and see if the battery voltage drops to the 12v range and stays there or slowly drops even when the egine is revved.
3) If the voltage drops in 2), then try another VR. If the voltage does not drop, then the filed or that filed brush is shorted to the alternator case and is casuing a constant full tilt charge.
 
I'm reading 14.2v at the blue wire and 15.3v at the battery. So I'm guessing I have a voltage drop or wiring issue. I used 16 gauge wire to replace the blue field wire and ran it back to the factory splice and soldered it in there. Should I switch to 10/12 gauge wire?
 
16 ga is plenty large enough for the blue wiring. It would be nice to see less drop, but that drop is not all that bad. But, you need to measure these voltages at fast idle; if the 15.3 volts is a regular low idle, then the VR is not doing its job. I am suspecting that the VR is not operating at the proper set point. How is the grounding to the VR? A good bare metal contact? And the battery ground to engine and chassis? You can measure between the battery - and the VR case to be sure that is almost 0.0 volts.

And is this VR a non-brand name unit? I was working with another fellow recently who went through 2 chain store brand VR's, and everything became good when he put in a new Wells VR.

And I don't want to waste your time but measuring the voltage drops from the VR back to the battery would be a good idea, just to be sure it is not unusually high at one point.

And this is not necessarily and issue at this time but.... What type of fuse and fuse holder are you using? If it is a standard blade type automotive fuse, the holders are not rated at more than 30A and you will likely have problems with that over the long term.
 
The VR casing is the ground right? I added a 10 ga wire from one of the mounting screws to the battery because I suspected ground might be the issue as it is not bare metal there. The ground to the block is a 4ga, but the only chasis ground I've seen on it is a 10ga to a mounting screw for the starter relay. I'll have to check the voltages when I go back to work on it next week and install the headlight relays.

I've got a Duralast (autozone) and BWD (advance auto) VR and both give me over 15v at the battery. Maybe I should look for a Wells VR after checking my ground and voltage drop again.

Thanks for asking about the fuse holder (electrical is not one of my strenghts). I was actually using a regular bladed fuse and fuse holder on a 12 ga wire running from the alternator to the starter relay. I decided I should beef up the wiring and fuse holder after reading up on some other threads and since I went with a slightly bigger alternator. Now its 8 ga wire from the 78A alternator running directly to an Optima red top battery and a maxifuse holder with a 40A fuse.
 
Very common question that gets answered regularly. Just search the posts by 67Dart273. He has the most patience with people who say they want to fix it but don't want to understand basic electricity or how the charging system works.

I'll just mention one tidbit. If the voltage drop from case of VR to its IGN1 input wire is ~14 V w/ engine running, it is doing its job.
 
Just a suggestion: I would not ever use a MaxiFuse in a power circuit like that which is subjected to large currents and the moisture of auto use; it would be Ok for temp use for troubleshooting but not for permanent installation. A MegaFuse and holder is all I would consider.
[ame]http://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/bolt-down-fuses/littelfuse_mega_datasheet.pdf[/ame]

Yes, the VR case is the ground. Sounds like it ought to have a good ground with your extra wire.

How hard wuld it be to move the alternaotr main output lead from the battery to the starter relay's big lug? There was a case here in the last few months where the poser had erratic charging voltage, and it all settled down when he moved the alternator wire to the starter's big lug. It gets it a bit closer to the VR.

And I agree with Bill's comment: the VR should be set so that it will put put proper voltage when the voltage between it's blue wire power input and it's case is around 13.5-13.8v. You have higher voltage (IF there are no ground circuit voltage drops), and yet the voltage is not regulated properly.
 
You must log in or register to reply here.
-

Back
Top