Negative Ground Conversion and Alternators

[mung]

I am getting ready to do my DC work and convert to negative ground.  My 4104 has already been changed to a belt driven alternator that at least externally looks to have the terminals isolated from the body of the alternator.  If I disconnect the wires and put my meter from the posts to the body and there is no internal connection to the body, would I need to change anything in the alternator?  If the body of the alternator isn't electrically part of the circuit, why would the alternator even care which battery terminal is attached to the body of the bus?

Vern

[eagle19952]

It shouldn't but the voltage regulator and the Ammeter and or Volt meter might

[mung]

Yes, I was aware of those items as well as the alarm rectifier. 

[bevans6]

Many, if not most, alternators use the body for the ground path, be that positive or negative.  It would be somewhat rare to have an alternator with the body floating with respect to ground.   Not to say you don't have one, I've just never seen one.  Does it have both a large positive voltage and negative voltage terminal?

Brian

[mung]

It has a positive and negative terminal, I had a little drama with it, but it turned out to be a blessing in disguise.  I didn't see the terminal markings at first, and when I did a quick test of the reversed battery, the regulator on the alternator let out a little magic smoke.  Not sure if it really did damage though, as it seems to still have continuity.  I did order a new regulator though, figuring if it didn't go now, it would go at some point. 

Anyway, when I removed the alternator to put it on the bench, I noticed that the adjustment bracket and the back bracket were broken and it was only being held on with the front bracket.  If that wasn't bad enough, the back bracket had broken off one of the bolts that hold the engine shutoff valve in place.  That would have been a bad thing to have figured out with the engine running at some point.  So, I got the broken bolt extracted last night and will get a replacement for that.  I am making a new back bracket and will weld the adjustment bracket.  When I put the alternator back on, I will swap the leads and hope that it works right at that point. 

Vern

[gus]

I have a diesel fire truck that has pos ground and the alt is also pos ground with only one power terminal.

I don't see how a neg ground alt could be mounted to a pos ground system, it would be tough to isolate the mount??

[mung]

It is very close to this alternator, if it isn't the same one.  Unfortunately, the earlier pictures I had found didn't have the + and - terminals so that is why I thought it didn't care.

http://www.prestolite.com/pgs_products/specs.php?item_detail_id=10410&item=A0012800JB&product=ALTERNATOR

Vern