alternator grounding

[morris]

Hi all, very simple question, is my alternator body supposed to be grounded to the engine block (and hence back to the fuse box -ve via the main engine ground strap)?

All my new bracketry and the block itself is now nicely painted and it suddenly occured to me that this might not be such a good thing in this instance as the whole thing will be isolated electrically or at best, grounded badly.

There are two electrical connections on the alternator itself but I remember coming to the conclusion, during my loom fiddling, that though one is red and the other black that they're both actually positive. I think one is the charging path back to B+ and the other provides a lower current to allow the alternator to do it's thing (technical term) in the first place, hence the need for a separate, non cable based ground somewhere in the system.

[Chris Cussen]

Yes, the alternator is grounded by its casing, so you will need an electrical path back to the battery. I would expect by the time you have bolted everthing down tight that somewhere a path ill exist. If not you will need to put a short earthing strap from the alternator to the engine block, but I doubt very much that you will need to do this.

If you have two terminals on the alternator then the big chunky one is indeed the charging path and should go to the battery +ve.

The other energises the alternator and comes through the ignition warning lamp.

[morris]

As I suspected then. I've put the paint on pretty thick so as you say a path will exist where it has been scratched by a bolt or something but it will be a weak one. I'll see if it's easier to run a strap or just sand back some paint in a discreet place.

thanks

[Mike]

Originally Posted by morris

As I suspected then. I've put the paint on pretty thick so as you say a path will exist where it has been scratched by a bolt or something but it will be a weak one. I'll see if it's easier to run a strap or just sand back some paint in a discreet place.

thanks

Ian

Although I have very limited electrical know how, I think you can easily test your alterator earth by testing a light bulb circuit from the battery +ve to the alternator case. If it glows you have your earth!
Or if you have a continuity meter ...................
Mike

[morris]

I had to take it back off today to do some cleaning and painting anyway but prior to that I whacked a multi-meter between the case and the cylinder head and got a beep so there is a path but I may run a little strap acros s anyway just to give a good path for higher amps

[atlantasportster]

Originally Posted by morris

I had to take it back off today to do some cleaning and painting anyway but prior to that I whacked a multi-meter between the case and the cylinder head and got a beep so there is a path but I may run a little strap acros s anyway just to give a good path for higher amps

Remember--DC flows in a loop, the grounding components should be able to handle the higher amps needed to start the engine from a weaker battery.
In our Cobra builds we will often weld in a 9mm stud to the chassis, and repaint the area.

[MartinClan]

Originally Posted by morris

I had to take it back off today to do some cleaning and painting anyway but prior to that I whacked a multi-meter between the case and the cylinder head and got a beep so there is a path but I may run a little strap acros s anyway just to give a good path for higher amps

Multi-meter can be pretty useless in this situation because it will normally show continuity even if there is a few ohms resistance. You need less that 0.01 ohms. The leads of most multimeter's have more resistance than that! Best thing is just to make sure you have a bare metal to bare metal path and it should be fine.

Robin