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Author Topic:   Battery Disconnect switch
dirtbandit
Dirt Maniac

Total posts: 110
posted January 25, 2005 07:38 AM  
getting ready to wire car for the first time and was trying to figure out if you hook the battery disconnect switch on the positive or negative lead? I originally planned on grounding the negative to the frame and running a jumper from the motor to the frame.

Thanks,

Dirtbandit

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 25, 2005 08:21 AM  
Switch the positive. That way if you have a cut or loose wire somewhere you can flip the switch and keep it from arcing.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted January 25, 2005 09:10 AM  
i dont know alot about electricity, but i am thinking of going to the negative side because of a few reasons.
1) some tracks mandate behind the seat so an outside worker can get to it easy, so instead of running 10 feet of cable to behind the seat then forward, it would be less cable to just put it on the neg, which already grounds behind my seat.
2) as far as kill switch goes why are they in reach of the driver at some tracks??? the ignition switch is within my easy reach, and will shut off the motor also, i would almost bet most all drivers will reach for that one before the master kill(given both are within reach).

but what would be some downfalls to putting the main disconnect on the neg side? is this a bad idea? like i said i am not an electritician, and this will be my first time wiring the car also.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 25, 2005 10:14 AM  
If you switch the ground from the battery to the frame it would do the same but i think it is general practice to switch the positive wire. Also if you ever had something else like bent sheet metal or something complete the ground from the battery to the frame the switch would be no good, whereas in the positive side it would still shut everythign down.

I was thinking about our car where the batery is on the right so in order to switch the negative we would have to run a lot more cable, than simply switching the positive side.

I dont know why they place them where they do. I can see the advantage of having one that a worker can find easlily. The only reason I can see the driver needing one is to shut off al power not just to the engine, if he has seperate accessory switches. I dont really know though. WE dont have to run them so its something i havent really thought about.

donslink1
Dirt Freak

Total posts: 318
posted January 25, 2005 03:48 PM  
Dirtbuster I am with you 100%

FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted January 25, 2005 04:16 PM  
Everything said here has a good point. If you do switch the ground side, yes there is a possiblity of a short if a wire breaks and grounds out and you can't turn it off with the switch. My car's switch is on the positive side for that very reason.

But let me clear up why some people do switch the ground. By switching the ground side you have a cleaner and smoother engagement and disengagement of power. When you switch power on and off whether it be ground or power side, there will be a voltage spike. By using the ground to switch, the spike is much less. That is the only reason I could see to switch the ground, and that would benefit systems that are very sensitive to voltage spikes and other variations. Most likely systems that will not be on a race car. Modern day engine contollers are sensitive to voltage spikes and variations. Most people don't know it but current day engine and other system controllers(on new vehicles) only run off of 5 volts. 12 volts will fry them. When you are handling a contoller you have to be careful, because static electricity will destroy it. Hope that clarifies why some people switch the ground side. But no I don't think its neccessary for a dirt car! LOL!!

[This message has been edited by FlyNLoIMCA17 (edited January 25, 2005).]

mod70
unregistered Total posts: 753
posted January 25, 2005 05:29 PM           send a private message to FlyNLoIMCA17   Edit/Delete Message   Reply w/QuoteBBBBBB
Hey zero, check our rules. They specificaly state that the switch must be connected to the positive wire. Bandit, you may want to look into this also.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted January 25, 2005 05:33 PM  
when they read thier own rules i will follow them closer. if i put the disconnect on the pos one and behind my seat then my pos. wire will snake around the car. so i guess just leave it in the drivers reach.
good point about the wire coming off, as far as sheet metal getting into it that is not a problem(if sheetmetal gets into it that is on the bottom of my list of worries.

[This message has been edited by zeroracing (edited January 25, 2005).]

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