Does a external alternator regulator have to be grounded?

panel · Post by **panel** » Sun May 06, 2007 8:02 am

Does a external alternator regulator have to be grounded? I have a 911 fan/alt on my bus and wondered.

Post by **david58** » Sun May 06, 2007 8:17 am

It is grounded by the bolts that attache it to the sheet metal.

Post by **Marc** » Sun May 06, 2007 9:54 am

It's best if there's a ground wire connecting the alternator and the regulator...but if both are connected via a good chassis-ground it'll work without that.

panel · Post by **panel** » Sun May 06, 2007 12:38 pm

David58bug wrote:It is grounded by the bolts that attache it to the sheet metal.

Not if it's hanging off of a hose outside the motor compartment

and there is no sheet metal with a 911 fan shroud.

MNAirHead · Post by **MNAirHead** » Mon May 07, 2007 9:27 am

I've always been instructed to use a grounding wire (just in case).. normally there's a screw terminal... note most magnesieum develops a white chalky or dirty looking haze that becomes resistance.

NOTE... if you do not have a positive ground the wire should be thicker than a flimsy brown one.

Post by **Tom Notch** » Mon May 07, 2007 9:35 am

The couple of 911 style chopper gun shrouds I've dealt with always had the VR bolted to the top of case inside the shroud.

Post by **Marc** » Mon May 07, 2007 10:17 am

MNAirHead wrote:I've always been instructed to use a grounding wire (just in case)....the wire should be thicker than a flimsy brown one.

The three wires connecting the alternator & regulator (D+, D-, DF) should be all that's needed for the charging system to function properly, it's just considered good practice that the regulator housing be grounded.
If you should ever lose a solid ground for the alternator, say from corrosion developing between the housing & pedestal, the added little ground wire could be called upon to handle far more current than it's capable of.
Consider cars which use a braided ground strap for the alternator (primarily because it's rubber-mounted). If it goes between the alternator and the chassis, and the larger chassis-to-engine block ground strap fails, it will end up having to handle the starter motor current. If it happens to be routed inside the main engine wiring harness (as it is in many Fiats) when it overheats it can melt other wires' insulation and cause all sorts of problems. Moral: if your regulator is not mounted to chassis ground, adding a small ground wire between it and the alternator, although not really needed, can do no harm. If it IS grounded to the chassis and you add a wire, it should be small enough to be "sacrificial" (i.e. it'll burn itself up before taking out its neighbors) or it should be routed away from any other wires or fuel lines to minimize the damage if the main ground ever fails and it suddenly has to pass big current.