12v power socket question

[Guest]

the one i bought doesn't have instructions.
+ve to the center, right?

 

[mailbox]

Yes, unless you smell smoke, then NO!!!

 

[Steve_S]

If it's a positive ground car, you better not let the outer (negative) touch anything metal.

 

[Guest]

It's not. It's -ve ground.

 

[angelfj1]

Alan: If the complete housing is insulated (plastic)it doesn't really matter. Just remember to be consistent in your connections. If the outside (shell) is metal be sure that you use this for earth. For example positive for early TR's and negative for later.

 

[martx-5]

Wouldn't using the outside shell for earth on a positive ground car reverse the polarity of the socket?? Those sockets are usually used to power stuff that is polarity sensitive, and is looking for the center terminal to be positive.

 

[Guest]

That was my point. I only want it for the phone and the GPS.
It's +ve to the center, which is what I figured, since having 12v unshielded mounted to the car body (screwed in place) would be kinda dumb.

In fact now I think about it for a second or two, that answered my own question :blush:

 

[Steve_S]

Wouldn't using the outside shell for earth on a positive ground car reverse the polarity of the socket?? Those sockets are usually used to power stuff that is polarity sensitive, and is looking for the center terminal to be positive.

Yes, exactly. This is why I mentioned positive ground versus negative ground cars. On a positive ground car you have to insure that the outer is insulated from the metal chassis of the car or else you get a major short circuit. The only other way is to connect it reversed to match the car, and use a cable adapter to reverse it back for the items you plug in.

 

[angelfj1]

Like I said, it makes NO difference if you are consistent. But, if you want to avoid any future confusion, follow these steps:
For positive earth car
If the mounting bracket is electrically connected to the "shell" inside the connector you must electrically isolate the unit from the chassis when mounting, by using a piece of non conducting material (plastic) between the unit and chassis.
Then connect the negative terminal side of the battery to the outside shell and the positive to the inner conductor. Always use a fuse in series.

For a negative earth car
If the mounting bracket is electrically connected to the "shell" inside the connector you don't need to do anything special because the earth connection IS part of the structure of the car. Just connect the inner connnector to positive through a fuse.

The above assumes that you are connecting modern electronic accessories which might be polarity sensitive. Most of these now have blocking diodes which will protect from inadvertant polarity errors. Caution, if you are using original period devices be very careful. These older devices DO NOT have the blocking diode safety feature. They also have early semiconductors, e.g. transistors and diodes which will fail immediately upon reverse polarity.

good luck

Good luck