MoparFins

Techical Discussions => Tech- - ELECTRICAL => Topic started by: attkrlufy on January 13, 2011, 07:20:40 AM

Title: Why cutoff negative line and not positve?
Post by: attkrlufy on January 13, 2011, 07:20:40 AM
It's a slow month and I've always wondered:

Why are battery cutoff switches installed on the negative line and not the positive?  If you're just trying to disrupt the circuit (for storage or safety or whatever) then why does it matter which terminal is cut-off?  I've never seen a switch installed on the positive battery terminal.  Is there a reason?


Title: Why cutoff negative line and not positve?
Post by: Rich on January 13, 2011, 07:35:33 AM
Revolutions number 9 paragraph 9 states: thou shalt not disrupt thy positive flow, less thee would like to glow like thy burning bush.
 Seriously, I have no idea.  Now I  wonder about how old 6 volt positive ground systems were interupted.
Title: Why cutoff negative line and not positve?
Post by: Snotty on January 13, 2011, 09:44:36 AM
My guess would be that most negative cables are single and on;y go from teh battery to the ground point.  But, most positives have additional wires that come off of the positive cable and go to places like the starter relay, or someplace else.  I would think there is less of a chance of interfering the flow by cutting the negative cable.
 
I know that my '70 Challenger had two wires that came off the positive cable, and one went to a ground point on the radiator support.  If that nut were loose the car would not start.  If it came loose while driving my entire elecrtrical system would act up.  ???
Title: Why cutoff negative line and not positve?
Post by: Steve on January 13, 2011, 10:11:44 AM
You can't surge the ground
Title: Why cutoff negative line and not positve?
Post by: Stitcherbob on January 13, 2011, 03:38:13 PM

with the positive cable off and ground still connected, won't the car still run off it's alternator?

which is why drag racers have safety switches to cut the power in an emergency
stitcherbob2011-01-13 20:39:04
Title: Why cutoff negative line and not positve?
Post by: Jason Goldsack on January 13, 2011, 04:13:48 PM
I always cut off the positive cable on my Drag Car and had a switch in the car to kill the field wire while racing so the kill switch would work. Then I could re-energize the alternator to drive on the street to charge the battery.. Running without the alternator charging was worth a tenth of a second on a high 12 second car..

You are correct that a mopar will run off the alternator with the power cut, but not if you cut the field wire.


Title: Why cutoff negative line and not positve?
Post by: Steve on January 13, 2011, 04:28:16 PM
[/QUOTE]


 
Jason is correct.  It's a quick, dirty way of checking if the charging system is working.  However, there is a chance the voltage could be too high and burn things out though.   The battery acts as a reference for the regulators on these newer cars.  It's supposed to be Taboo to disconnect the batery in these new guys
Title: Why cutoff negative line and not positve?
Post by: Jason Goldsack on January 14, 2011, 01:39:48 AM
I will say one thing about switching the negative.

When I ran my pusher electric fan on my drag car I kept burning up switches. I was turning the positive on and off. I then changed to having the toggle switch control the negative and I wired the fan directly to my battery. Never burned out another switch as no juice runs through the negative.




Title: Why cutoff negative line and not positve?
Post by: Steve on January 14, 2011, 12:10:29 PM
You're supposed to relay the fans
Title: Why cutoff negative line and not positve?
Post by: attkrlufy on January 14, 2011, 12:49:06 PM

Quote from: POLARACO
You can't surge the ground
Yeah, but I'm not drag racing.  I'm thinking about using the cut off only when the car's not running.  It's for A) long term storage and B) so I don't have to disconnect the neg line each time I want to work on the car - to avoid zappage and exploding batteries (sparks near batteries make me nervous).

So does it really matter which line I choose in this type of situation?

Title: Why cutoff negative line and not positve?
Post by: Jason Goldsack on January 14, 2011, 01:12:35 PM
Relay? I guess that would have saving some switches LOL

Switching the ground worked great for 8 years though.. LOL