Moparts

Alternator Grounding

Posted By: jeebis44

Alternator Grounding - 04/25/13 12:42 AM

Question: I just got a rebuilt 114 amp alternator for my '83 Plymouth Gran Fury cop car, and the rebuilt unit does not have a ground post installed, only a hole marked GRD. The old alt does have the post and was grounded to the pass. cylinder head. How do i fix this? Can I just thread a screw into the hole and run it like that? Ground the casing to the cylinder head?? I've attached a pic of my old alt. - the new one just has a hole where I circled in yellow...
Posted By: jeebis44

Re: Alternator Grounding - 04/25/13 12:43 AM

A pic of the front - 114 amp cop car alternator
Posted By: skicker

Re: Alternator Grounding - 04/25/13 01:05 AM

I'd try using the bolt that holds the case together??
Posted By: jeebis44

Re: Alternator Grounding - 04/25/13 01:31 AM

Do I just need to ground the casing? Or is there something inside that needs to be grounded?
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 01:39 AM

Quote:

Do I just need to ground the casing? Or is there something inside that needs to be grounded? [/quote

I would be willing to bet its just a case ground. The way to check? SIMPLE! Just put a continuity or ohmmeter on the stud and case and check for continuity!
Posted By: cjskotni

Re: Alternator Grounding - 04/25/13 02:36 AM

The stud is simply a stud screwed into the casing. Normally, the bolt that holds the alternator to the brackets would be sufficient to ground but running a jumper wire from that ground stud to a bolt on the engine block wouldn't hurt.

Don't overthink it. It's just an additional point where you can ground from. That's it.

Not a bad idea to use it to make sure your grounds are 110% but not absolutely needed.
Posted By: jeebis44

Re: Alternator Grounding - 04/25/13 03:18 AM

Thanks for the replies. So then, I should be able to check for continuity between the case and the engine block and if it's there, I'm good?
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 03:26 AM

Quote:

The stud is simply a stud screwed into the casing. Normally, the bolt that holds the alternator to the brackets would be sufficient to ground but running a jumper wire from that ground stud to a bolt on the engine block wouldn't hurt.

Don't overthink it. It's just an additional point where you can ground from. That's it.

Not a bad idea to use it to make sure your grounds are 110% but not absolutely needed.



That is wrong. That alternator needs a hd ground. It has rubber isolators for mounts thats why there was a wire when the car was built.
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 03:30 AM

Quote:

Thanks for the replies. So then, I should be able to check for continuity between the case and the engine block and if it's there, I'm good?



Yes, correct. Just as long as there is a good reliable metal to metal connection.
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 03:30 AM

Quote:

Thanks for the replies. So then, I should be able to check for continuity between the case and the engine block and if it's there, I'm good?



No.. You want to use a heavy guage wire from that stud to the engine. All the factory cars and trucks had a ground wire. You alternator is mounted with rubber isolators thats why there was a HD wire on the car. I would ask for another correct alternator.
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 03:35 AM

Quote:

Quote:

Thanks for the replies. So then, I should be able to check for continuity between the case and the engine block and if it's there, I'm good?



No.. You want to use a heavy guage wire from that stud to the engine. All the factory cars and trucks had a ground wire. You alternator is mounted with rubber isolators thats why there was a HD wire on the car. I would ask for another correct alternator.



"That stud" represents nothing more that an electrical connection to the case. As long as the the alternator is NOT isolated (electrically) he's fine. I did not read they the posts carefully, but I thought he is using this alt in a non stock application. I could be wrong.
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 03:39 AM

Now I see. The alts mounting bosses are isolated. All that would be required would be to reliably defeat this isolation. That could be by using the ground stud as designed, or by defeating the isolation itself.
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 03:41 AM

Quote:

That stud" represents nothing more that an electrical connection to the case. As long as the the alternator is NOT isolated (electrically) he's fine. I did not read they the posts carefully, but I thought he is using this alt in a non stock application. I could be wrong.




You are very wrong. His whole post is full of mis-information. That alternator is rubber isolated mounting. Look at the rubber mounts. The stud is there for a reason. That unit is very power full and needs a correct ground. Why do you think the factory used it and had about a 10 or 8 gauge wire on it??? Come on you guys smarten up.
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 03:44 AM

Quote:

Now I see. The alts mounting bosses are isolated. All that would be required would be to reliably defeat this isolation. That could be by using the ground stud as designed, or by defeating the isolation itself.



You don't want to eliminate the mounts. They help make the alternator last longer, run cooler and from what I remember cut down on RFI as they were mainly used in police and taxi.
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 03:53 AM

Quote:

Quote:

Now I see. The alts mounting bosses are isolated. All that would be required would be to reliably defeat this isolation. That could be by using the ground stud as designed, or by defeating the isolation itself.



You don't want to eliminate the mounts. They help make the alternator last longer, run cooler and from what I remember cut down on RFI as they were mainly used in police and taxi.



So the millions of alternators that are solidly and electrically mounted are doomed? Not saying you're wrong, just saying you're being extreme. In The typical moparts fashion. Lighten up.

If the OP doesn't want to do add any wiring, fine....if he doesn't care then do it!
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 04:03 AM

Quote:

So the millions of alternators that are solidly and electrically mounted are doomed? Not saying you're wrong, just saying you're being extreme. I. The typically moparts fashion. Lighten up.

If the OP doesn't want to do add any wiring, fine....if he doesn't care then do it!



No they are not doomed. The problem here is you gave incorrect advice on a designed system that you clearly know nothing about. You should admit the incorrect advice and take a back seat and learn something.

He needs to correctly ground that alternator. If not what that unit gets full fielded it will look for a ground and burn up what ever it can trying to find it. The op even states it was grounded by that stud to the head by a wire. Do it right and he wont have issues.
Posted By: ahy

Re: Alternator Grounding - 04/25/13 04:03 AM

I run the "big Chrysler" alternator also. As posted, the alternator mounts are rubber isolated - unlike the typical round back or square back. The big alternator needs a heavy ground from the case to to engine head or block to function correctly. Good sized block to chassis grounds are needed also. The OE ground on my donor vehicle looked like 6 gauge so that's what I used. Same size for the power wire (+).
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 04:05 AM

Quote:

I run the "big Chrysler" alternator also. As posted, the alternator mounts are rubber isolated - unlike the typical round back or square back. The big alternator needs a heavy ground from the case to to engine head or block to function correctly. Good sized block to chassis grounds are needed also. The OE ground on my donor vehicle looked like 6 gauge so that's what I used. Same size for the power wire (+).



Finally someone else that can tell it like it should be.
Posted By: jeebis44

Re: Alternator Grounding - 04/25/13 04:06 AM

OK - This is in a relatively stock car, used for daily driving. Rubber mounts are intact, and using a multimeter, found continuity between the alt. case and engine in several points without the ground wire hooked up. That said, I did upgrade the ground wire years ago to about an 8 gauge wire... would like to keep it that way, if for no other reason than vibration may cause issues down the line ( i drive the thing like a a maniac...). Main point of my original question was to find out exactly WHAT needs to be grounded here, and from all posts to now, it's the case. Simple fix IMHO. Tap and screw into the original ground hole in the case and hook up my HD ground wire going right into the pass. side cyl. head. Am I wrong?
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 04:08 AM

Quote:

Quote:

So the millions of alternators that are solidly and electrically mounted are doomed? Not saying you're wrong, just saying you're being extreme. I. The typically moparts fashion. Lighten up.

If the OP doesn't want to do add any wiring, fine....if he doesn't care then do it!



No they are not doomed. The problem here is you gave incorrect advice on a designed system that you clearly know nothing about. You should admit the incorrect advice and take a back seat and learn something.



He needs to correctly ground that alternator. If not what that unit gets full fielded it will look for a ground and burn up what ever it can trying to find it. The op even states it was grounded by that stud to the head by a wire. Do it right and he wont have issues.



Please show me where I advised that it does not need to be reliably grounded? Clearly the ground stud is to facilitate isolation.
Again...lighten up. Stay grounded.
Posted By: ahy

Re: Alternator Grounding - 04/25/13 04:09 AM

Sounds right to me.

Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 04:13 AM

Quote:

OK - This is in a relatively stock car, used for daily driving. Rubber mounts are intact, and using a multimeter, found continuity between the alt. case and engine in several points without the ground wire hooked up. That said, I did upgrade the ground wire years ago to about an 8 gauge wire... would like to keep it that way, if for no other reason than vibration may cause issues down the line ( i drive the thing like a a maniac...). Main point of my original question was to find out exactly WHAT needs to be grounded here, and from all posts to now, it's the case. Simple fix IMHO. Tap and screw into the original ground hole in the case and hook up my HD ground wire going right into the pass. side cyl. head. Am I wrong?




You're correct. There is nothing wrong in your fix!
Posted By: NITROUSN

Re: Alternator Grounding - 04/25/13 04:30 AM

Quote:

OK - This is in a relatively stock car, used for daily driving. Rubber mounts are intact, and using a multimeter, found continuity between the alt. case and engine in several points without the ground wire hooked up. That said, I did upgrade the ground wire years ago to about an 8 gauge wire... would like to keep it that way, if for no other reason than vibration may cause issues down the line ( i drive the thing like a a maniac...). Main point of my original question was to find out exactly WHAT needs to be grounded here, and from all posts to now, it's the case. Simple fix IMHO. Tap and screw into the original ground hole in the case and hook up my HD ground wire going right into the pass. side cyl. head. Am I wrong?



You need to ground it as I have said. You will find continuity with a multimeter only because it is finding it through incorrect sources. When you load it the loss of ground will be obvious. That alternator will not work through isolators. You are on the right correct path by using the ground wire to the case. I am done with this post and wish you luck. As far as the uneducated stupid posters that want to argue when they are wrong carry on. I laugh all day long at fools like you.
Posted By: jeebis44

Re: Alternator Grounding - 04/25/13 04:37 AM

What I am reading from these posts is this: ground the alternator case to the engine and the engine to the frame via direct heavy connections (metal-metal heavy gauge wires).
Posted By: Pacnorthcuda

Re: Alternator Grounding - 04/25/13 04:52 AM

Quote:

What I am reading from these posts is this: ground the alternator case to the engine and the engine to the frame via direct heavy connections (metal-metal heavy gauge wires).



Pre 80's it was usually grounded vis a the mounting of the unit. If the alternator has isolated mounts then either a mount needs to be electrically bypassed or the grounding stud utilized by wiring to a suitable ground, preferably the engine. You are good to go.
Posted By: 383man

Re: Alternator Grounding - 04/26/13 03:48 AM

Quote:

Quote:

Thanks for the replies. So then, I should be able to check for continuity between the case and the engine block and if it's there, I'm good?



No.. You want to use a heavy guage wire from that stud to the engine. All the factory cars and trucks had a ground wire. You alternator is mounted with rubber isolators thats why there was a HD wire on the car. I would ask for another correct alternator.




Yep that is dead on right. It needs the ground wire because of the rubber mounts on the alt. Most alt bolt right to the block but some such as this use rubber mounts and need the ground wire. You just have to ground the alt case. Ron
Posted By: Moparteacher

Re: Alternator Grounding - 04/26/13 05:21 AM

Once you have installed the alternator, using a continuity test to confirm ground is an inferior test. Perform a voltage drop test with the engine running and alternator at full field. Good results should show no more that .2V to .4V. And, .4V would be high, IMO.

Because the alternator case is insulated with the rubber mounts, the ground wire will need to carry the same amount of current that leaves the alternator. So, if the alternator is capable of driving 140 amps then the ground will need to carry 140 amps. Secure the ground wire to an unpainted surface on the engine.
Posted By: cjskotni

Re: Alternator Grounding - 04/26/13 12:06 PM

Who knew so many people would become so emaotional about this simple question!

In my earlier post, I did not realize this had rubber isolators on the mounts. In that case, you will most definitely need to use the ground wire on that stud. I would use an 8 ga wire or bigger. As said before, run it to the engine block and make sure the engine is grounded well via ground strap.

I am used to the old school, "we never use ground wires just ground through the mounts" electrical components. The older non-isolated alternators just grounded through the mounts (no rubber) so that's what people here are probably thinking of....
Posted By: denfireguy

Re: Alternator Grounding - 04/26/13 02:44 PM

The problem here is that a lot of people have never seen a cop car alternator. Having rebuilt several of these in the day, what Nitrous is saying is spot on. The only way to get a high current connection is through a 10 gauge (8 is way better) direct to the block.
I have not seen a cop car alternator in the rebuilt market. That is why we did our own in the day. The only wear items are the bearings, brushes and diodes. When we had a bad alternator, we shot gunned them and replaced all of the above parts. We did have one with a short in the stator and we took that to a motor winding shop (try to find one of those today) to be redone.
Craig
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