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  #1  
Old 07-24-2005, 03:34 PM
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Battery shut off switch

Alright electrical geni out there. We're looking for a battery cut of switch and have 2 questions

1. What amp rating does it need for continuous amps?
2. Do we need an alternator kill switch as well or will it die when battery is cut?
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Old 07-24-2005, 03:40 PM
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If you wire it so that you cut the battery off completely then yes alternator won't do you aything if its not running. You can find kits from places like summit or raceshop etc. but other wise I'd say get an amp kit 4guage or better if your going to do it custom.
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  #3  
Old 07-24-2005, 04:02 PM
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Quote:
Originally Posted by thundering02
If you wire it so that you cut the battery off completely then yes alternator won't do you aything if its not running. You can find kits from places like summit or raceshop etc. but other wise I'd say get an amp kit 4guage or better if your going to do it custom.

Well it has to be SFI legal so it will need to be manufactured by someone. Cutting it off completely (as in all the positive gone will shut it down???) Battery of course is in the trunk so running wires forward to shut off the alt wouldn't be fun, especially if I don't have to add the extra 5 ounces.
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Old 07-24-2005, 04:47 PM
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If the engine is running when you disconnect the battery, the alternator will continue to run and produce voltage. I've heard it said that this can damage the car's electrical system, but I've never heard of it happening. Enough current is drawn during normal operation of the engine that some degree of voltage modulation will occur and the alternator is not likely to fry anything. I can't speak from experience with an SVX, but I've done it and seen it done with many other cars. The voltage did not rise in any example I've witnessed.

Many alternators have a wire which runs directly to the positive battery terminal. There is usually another wire that goes directly to the starter motor, and one that goes to the fuse box for everything else. I'm not sure what the purpose of the disconnect is, but if you leave the alternator connected to the battery, and put the disconnect in the wire that goes to the fuse box, the alternator will be unable to power the car's electrical system when the disconnect is opened. There's really no need to provide a disconnect for the starter motor wire, but you can attach it on either side of the disconnect.

Presumably this is for racing. Do the rules specify what needs to be disconnected when the switch is thrown? Obviously, if the alternator is left in the circuit, the rules either recognize that the alternator is unable to produce anywhere near the amount of current that a battery is capable of and that it will fail if there is a sufficiently large short, or the rules are stupid and don't appreciate that the alternator will continue to function. It really depends on the purpose of the rules. Do you even care, or are you just trying to satisfy the regulations?
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Old 07-24-2005, 04:53 PM
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Quote:
Originally Posted by UberRoo

Presumably this is for racing. Do the rules specify what needs to be disconnected when the switch is thrown? Obviously, if the alternator is left in the circuit, the rules either recognize that the alternator is unable to produce anywhere near the amount of current that a battery is capable of and that it will fail if there is a sufficiently large short, or the rules are stupid and don't appreciate that the alternator will continue to function. It really depends on the purpose of the rules. Do you even care, or are you just trying to satisfy the regulations?
Car needs to die when it is pushed. Like a kill switch on a motorcycle
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Old 07-24-2005, 08:44 PM
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In that case, I'd just find the ignition wire and install a switch. Some of the nicer car security systems do this.

Still, if you leave the alternator connected, the car will probably continue to run. If disconnecting the ignition wire does not satisfy the rules, then the disconnect should go between the fuse box and the battery. On my SVX there's a lightly colored wire about a foot long that goes between the two. I don't know where the switch is supposed to be mounted, but I've seen people attach a piece of string to fuses or relays so they can just yank on it to shut off a particular device, usually the engine. It's cheesy, but it works.
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Old 07-25-2005, 03:15 AM
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Quote:
Originally Posted by benebob



Well it has to be SFI legal so it will need to be manufactured by someone. Cutting it off completely (as in all the positive gone will shut it down???) Battery of course is in the trunk so running wires forward to shut off the alt wouldn't be fun, especially if I don't have to add the extra 5 ounces.

I wire race cars and I am doing this project myself to my SVX. You need a master disconnect switch with a seconday circuit (normally called "with alternator disconnect/protect). There will be a pair of heavy duty terminals for going inline with the (+) side of the battery. There will also be a secondary switched circuit on it as well. Some people wire this inline with their voltage regulator for their alternator thusly killing it at the same time. For our car (SVX) it would be easier to connect the ignitor circuit to this second side of the switch, thusly killing the ignition when the master switch is flipped. I hope this helps.
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  #8  
Old 07-25-2005, 04:22 AM
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Hella Battery Disconnect Switch

Here's one made by Hella. It was standard fare in all IMSA prototypes in the 80's and 90's when I was building them. Summit Racing has them for around $18 (plus $8 for shipping). I have a brand new one I'll sell you cheap if you're interested. PM me.
Summit Racing Battery DisconnectsThe Hella battery disconnect is in the middle at the bottom of this link.
Don't let its price fool you; It's a well made switch. Once you remove the key, the switch acts like an anti-theft because without it (the key), you can't re-energize the car's electrical system.
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Last edited by gsodonis; 07-25-2005 at 04:27 AM.
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  #9  
Old 07-25-2005, 02:11 PM
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A buddy of mine has that switch. He was pretty ticked off when he found out that he couldn't remove the key when it was in the ON position. He installed it and then...what the? Dammit! (It sticks out the key cylinder hole for the rear hatch.) I was thinking about coming up behind him at a stoplight and swiping the key.
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