Battery Disconnect

I just got a battery disconnect switch from Summit Racing and I am thinking that it might be a better idea to interrupt the negative side of the battery rather than the positive side. That way I wouldn't have a full voltage wire coming through the firewall. Any opinions on this are welcome.

 

What is the intent of the battery switch, is it for theft or safty? If a resistance builds up in the switch it will not matter were you put it, it will still effect the current flow / voltage drop.

 

Marine battery disconnect switches recommend installation on the negative side.

 

I'm just thinking it may be a bit more difficult to isolate the ground on a vehicle. Most marine applications would require a separate ground wire to every electrical application unlike a vehicle where everything is grounded. The switch is for safety purposes. Resistence isn't an issue as it is rated at 175 amps and is waterproof.

 

thinking out loud
if a short develops, and you throw the ground disconnect, is it not too late anyhow, for the short is actually a ground, and this short will continue until you remove the power source from the wire ?

 

True, the circuits are the same though, just the means of ground (frame,copper buss, hull) and I do agree that isolating the ground in a standard vehicle could be difficult. But back to the original question, "I am thinking that it might be a better idea to interrupt the negative side of the battery rather than the positive side." I agree, but as stated before if there is current, arcing will be present, which will shorten the life of the switch. I would think putting the switch under the dash passenger side routing the neg. cable from battery through the fire wall and back to battery would be safe and simple. This is what I have in mind for mine, but I will be using a marine switch, being a marine mechanic they are plentiful and almost free they also have a locking switch.
Joe

 

If the switch isolates the battery, positive or negitive the power source is removed from the circuit no more short. I should say the short is still there but the electrical fire would go out!

 

yea
I thought of that as soon as I posted that dumb remark
going for more coffe now...

 

You should of seen my dumb reply before I drew a picture.

 

Thanks for the replies guys. I think I'll go stare under the hood for awhile and see what all I have connected to the neg side of the battery. Right off hand I know the compressor, winch and battery maintainer are. But then they are also connected to the pos side, so I guess it really doesn't matter. I may have to put in some sort of bus to distribute to ground to the various points ie:engine block, body, frame etc.

 

I wired mine on the positive side as it is a true kill switch. This way, when that switch is moved to the off position, the alternater will be cut off as well. You can see it hidden (in this picture anyway) by the grab bar. Maybe it's the same as yours?

 

Looks very similar. Did you run a separate wire to it from the alternator?

 

Yes. My alternator is a single wire GM so it was pretty easy. Ran the positive cable from the battery to the switch on one post. On the other post I ran the alternator wire and the battery cable to the starter.

EDIT- The alternator wire goes to the post with the cable that runs to the battery, not the starter. I had to re-think it, as I am not looking at it.

 

I'm still leaning towards switching the neg. terminal. I talked to a mechanic who works for the local fire dept and he said they have their equipment setup to shut off the neg/ground.

 

So is the primary reason for doing this is to have the ability to shut down the power source in the event of an electrical fire??

 

The primary reason could be different for different folks, a disconnect for a fire is one, i.e. racing. I find folks using the switch to preserve battery when Jeep is not used in a while, and I will use one for theft deterrent, it will be locking. Just a few reasons.

 

I have one on the neg battery post (got the removable one, don't care for the switch type). I use it for storage, and when doing any electrical work on the jeep. also with the tang on the post, VERY hard to mix the ground and hot wires.

 

Posi how about this?

http://www.painlesswiring.com/webcatalog.php?cat-battacc.htm#30204

The Remote Master Disconnect with Mechanical Latching Solenoid is what I was thinking. #30206

 

This is the style I will be using, mounted the lugs will be in the engine compartment, key under dash, it costs about $10.00.

For Safety:
Use this switch as a safe and easy way to cut power while working on your vehicle's electrical system.
For Security:
Hide the installation of this switch to provide simple theft prevention. Disable the operation of your car, truck or boat simply by removing the key.

Features:
Maximum voltage: 32Vdc
Maximum Surge Current: 500Amps for 10 seconds @ 12Vdc
Maximum continuous current: 100Amps @ 12Vdc
Removable Key
Two 3/8" Lugs

 

I just finished wiring the switch in yesterday. I'll try to post some pics on Tues or Wed.