Grounding alternator

[pjm8047]

i have a powermaster alternator on my 71 rr that I added 8 gauge power wire to it and with loads on im getting 12.8v is that normal? Im getting 14.8v no loads on. There is a ground stud on the back of the alternator will grounding it to the negative battery post help the voltage?

 

[66Satellite47]

What rpm 12.8 V? Maybe a little low, I'd hope for more like 13.2 V at 2000 rpm. The 14.8 V is pretty normal for no load @ about 1000 rpm.

 

[pjm8047]

Per vehicle spec 71 Service manual i sent my idle rpm at 800 rpms in neutral . Voltage does go up as I increase rpms.

 

[Glenwood]

An early style alternator has a single field and the GND terminal should be connected to ground. My 64 has is connected to the case internally.
from a 64

I would have thought your 71 would have a two field alternator which connects as follows:

Just be sure which one you have.

 

[Zeppelin264]

You can ground that post to the alternator housing itself. I just added a small wire and bolted it down to the back of the case. This means that your ground goes through the engine block so make sure you have atleast 1-3 grounds from the block to chassis.

I'm assuming this is a 1 wire setup. Also 8 gauge is pretty small, definitely do a voltage drop test to see if it's the wire size that's loosing your voltage.

 

[pjm8047]

Can i take one side ofa set jumper cables and ran one from the battery positve to the alternator positive to see if that makes a difference?

 

[pjm8047]

You can ground that post to the alternator housing itself. I just added a small wire and bolted it down to the back of the case. This means that your ground goes through the engine block so make sure you have atleast 1-3 grounds from the block to chassis.

I'm assuming this is a 1 wire setup. Also 8 gauge is pretty small, definitely do a voltage drop test to see if it's the wire size that's loosing your voltage.

If i get the same voltage at the alternator positive that im getting at the battery will increasing rpm to 1,000 at idle ok? Rpms drop below 800 with loads on.
https://goo.gl/images/EAuRzL

 

[72RoadrunnerGTX]

i have a powermaster alternator on my 71 rr that I added 8 gauge power wire to it and with loads on im getting 12.8v is that normal? Im getting 14.8v no loads on. There is a ground stud on the back of the alternator will grounding it to the negative battery post help the voltage?

Take some voltage drop measurements during these conditions, alternator ground stud, or case, to battery negative, should be 0 volts. Then from regulator ignition run feed (blue wire) to Battery positive, should not be more than .2-.4 volt. This will eliminate wiring-connection issues. Sounds like the alternator idle output is below where it needs to be.

 

[pjm8047]

Where should I have my idle set?

 

[72RoadrunnerGTX]

What engine-trans, A/C or not, original pulleys?

 

[pjm8047]

What engine-trans, A/C or not, original pulleys?

383 auto no ac original pulleys idle set at 800 rpms at idle in neutral. Drops below 800 when accessories are on.

 

[72RoadrunnerGTX]

The Power Master 95amp alternators should have a much better idle speed output over the original alternators. I would have it load tested, may have problem. Voltages posted seem correct. Idle speed? Raising the idle may help, with auto trans, 800-850 would be about as high as I would want to go. What accessories are you running?

 

[pjm8047]

Just turning on the headlights or wipers drops it to 12.8. Im gonna turned idle screw just a little to get around 13.2v. Is it normal for the engine speed to drop when headlights are on? My original alternator was doing the same thing.

 

[pjm8047]

So I think I solved my problem but haven’t tried it yet. I think I was using the wrong type of wire whole time currently have in the vehicle 10 gauge primary wire automotive in the vehicle I think that was the whole problem the whole time not big enough wire I ended up buying 10 gauge battery jumper cables that i will be cutting off the clamps and crimping on copper lugs to see if this works out hope it does. The reason I was using 10 gauge primary wire is because the person that sold me the alternator told me to use 10 gauge wire he did not tell me what type of wire to use I did not know there was a difference .

 

[Zeppelin264]

10 gauge even seems small. I think like 4 gauge is minimum and 2 or 0 gauge would be ideal.

 

[pjm8047]

i have a powermaster alternator on my 71 rr that I added 8 gauge power wire to it and with loads on im getting 12.8v is that normal? Im getting 14.8v no loads on. There is a ground stud on the back of the alternator will grounding it to the negative battery post help the voltage?

10 gauge even seems small. I think like 4 gauge is minimum and 2 or 0 gauge would be ideal.

Cars is stock. Ive read that a 10 gauge battery cable can push 60 amps. Id think that'd would be perfect.

 

[oldbee]

For the alt.output wire I would think maybe 8ga. I'm thinking 10 or 8 was standard. No big audio amp or power hungry add-ons right?

 

[Glenwood]

10 awg (qauge) is 10 awg. The type of wire insulation only matters for environmental conditions it is subjected to like heat oil etc. Changing the wire type but keeping the same gauge will not help with current flow in most cases.

Standard loads will likely not exceed 30-40 amps most of the time which a 10 awg is plenty. Inmo, 8 awg is a better size conductor to use between the alt and batt cable unless you have additional power loads such as amps etc.

 

[pjm8047]

All factory accessories only installed an aftermarket fan. The factory uses 12 gauge primary wire.

 

[oldbee]

Glenwood is correct, you may be thinking of welding cable versus regular cable. Welding has much finer strands of copper and is more flexible for running around bends. Carries same amount of current though, but u can't get it in anything smaller than maybe 2-4ga. Always remember that gauges with higher numbers are "thinner" wires.