Main battery disconnect

[Elmo Rodge]

For my main battery disconnect do I disconnect the positive or the negative (ground)?  Seems like everything I read says to disconnect the ground first when I'm doing anything. Wayno

[Milwaukee Midget]

Ground - the grounds on a vehicle are everywhere, so you eliminate ANY possibility of a short by lifting the ground.

Discovered that one when all the Lucas smoke left my MGB.

And when I shorted out my manual temp gauge on the Midget.

And when I installed the radio on my Cyclone GT.

And when I installed a CB in my Corvair.

And when, well, you get the picture . . .

[Elmo Rodge]

Thanx Chris.  That's the way I had it figured but, it takes me four tries to install the batteries in my flashlight.  Wayno

[Cajun Kid]

Hmm,, not the way I did it.

I have 2 batteries in the trunk.

Each battery is connected is connected to each other,,, pos to pos,,, neg to neg...

Bat 1     Bat 2
Pos >>> Pos>>> Disconnect Lug 1>>>Disconnect lug 2 >>  to front of car to main power grid.

Bat 1     Bat 2
Neg >>> Neg>>> Chassis Ground.

So when the Rear (main disconnect switch) is off,, NO power goes forward to any part of the car.

If I used a Neg Disconnect wouldn't the power still be hot to the rest of the cars and each individual ground would need to be disconnected ?  

Maybe , I am wrong,, but NEVER (knock on wood) had a problem on any Race cars I wired disconnects like this ?

Charles

[johnneilson]

I think the intent is to kill the power to the car and stop the motor, fuel system etc.
If for some chance you have an alternator on the car, disconnecting the ground will not stop the motor.

Of course, if you have a magneto ignition, the battery disconnect switch is useless.

Rule book does not stipulate shutting off motor, so why the disconnect switch on the end of car?

John

[Milwaukee Midget]

Oh, good lord . . .    Excuse me while I wipe the egg from my face.

Charles and John have it right.  Problems arise if you're running an alternator - it remains a power source in the circuit, as long as the engine is turning - your electrical kill will only take the battery out of the circuit.  A single throw, double pole is probably the safest answer.

Standing down . . .

[Stan Back]

"why the disconnect switch on the end of car?"

So they have a place to put the new, ugly sticker?

[johnneilson]

"why the disconnect switch on the end of car?"

So they have a place to put the new, ugly sticker?

There have been many discussions about this in other organizations. I like the one who allows for the switch to be in the drivers reach, inside the car.
That will assist a emergency worker when the car is inverted or laying on the drivers side.

John

[Dr Goggles]

Oh, good lord . . .    Excuse me while I wipe the egg from my face.

Charles and John have it right.  Problems arise if you're running an alternator - it remains a power source in the circuit, as long as the engine is turning - your electrical kill will only take the battery out of the circuit.  A single throw, double pole is probably the safest answer.

Standing down . . .

That way I understand it is that lots of that Pommy shite has pos earth....thus when you disconnect the earth you are disconnecting the hot side. The safety switch issue is to disconnect the hot side of the battery as close as practicable to the battery itself  as there is always the possibility that that line between the ignition( or somewhere else along the line)  and the battery contacts the chassis in the event of an upset....making problems worse despite the ignition being off........


And, yes, if you just disconnect the (negative) earth there will be a hot wire everywhere.......

This my friends is just hearsay, I have little electrical experience, and fewer skills. The Colonel on the other hand does. No doubt he will pipe up soon , deride me for even replying and put this all straight.


the back of a car is a good place for those things because unless the car is standing on it's end the switch will be accessable....there could always be a cable-pull to operate it from the cab.

[jdincau]

I think the intent is to kill the power to the car and stop the motor, fuel system etc.
If for some chance you have an alternator on the car, disconnecting the ground will not stop the motor.

Of course, if you have a magneto ignition, the battery disconnect switch is useless.

Rule book does not stipulate shutting off motor, so why the disconnect switch on the end of car?

John

The intent of the rule at least as far as the SCTA is concerned is to have the switch in a common outside location so first responders will know where it is. The switch is to disconnect the power so that extraction procedures will not cause sparks leading to fires.

[RidgeRunner]

the back of a car is a good place for those things because unless the car is standing on it's end the switch will be accessable....there could always be a cable-pull to operate it from the cab.
[/quote]


     That's the set up we are working on right now for the lakester build I am helping out on.

                         Ed

[Jon]

Doesn't make any difference if the isolation switch is on the positive or negative main lead as long as there is no wiring running parallel to it allowing a bypass of the switch.

If either the + or the - leads are disconnected the vehicle is not "hot" as a circuit cant be completed.

If running an alternator the vehicle can run with the battery isolated regardless which side it is isolated on.

Useless trivia; electrons actually flow from negative to positive.


Cheers
jon

[maguromic]

Both the REMR and the Firebird will have a solid state system, with one toggle switch in the car and one in the back. No moving parts to worry about and one less thing to go wrong. ( I know all to well what can happen) Tony

[Elmo Rodge]

I am running an alternator so I will pay attention to that. I think I'll try to invent a wiring diagram and post a picture of it here. All I know about electricity is that it is FM. (flippin' magic)  Thanx guys. Wayno

[gray63]

I have installed two 4 pole Cole Herse Kill switches on my car. One is at the rear of the car for easy access for the emergency workers and one at the drivers location. ( Just because I want access to it) I originally mounted the drivers kill switch too close to the shifter and killed the engine during a 2-3 shift at Bonneville. (Not great engineering I guess) Both of the switches interrupt the negative wiring.

Dave Gray # 3611
Carlisle, Pa.