Kill Switch/Battery Disconnect
02-02-2005, 06:06 PM
#1
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Kill Switch/Battery Disconnect
(thought I'd start a new thread for this)
Now, I don't claim to be the expert here, but PCA's club racing rule reads:
"18. An electrical cut-off switch, either externally mounted or with externally accessible pull wire - preferably on the driver’s side - is required. The location of the handle or pull must be indicated with the standard approved decal. The switch must disconnect the battery from all circuits except electrically operated on-board fire systems, and must shut off the engine while it is running well above idle speed. (See Appendix C)"
So I looked around at some other rule books, and most others have the same basic language (POC, BMWCCA, etc). The POC rule book even has a hand drawn picture that shows how to hook it up to the battery. Are these scantioning bodies all wrong?
Originally Posted by Doug Donsbach
First off, it isn't always the case that an engine will continue to run if the battery is disconnected. But it is likely enough that an additional mechanism must be used to prevent the alternator from self powering the hot side of the wiring. The most basic way to do this is to positively stop the engine when the kill switch is turned to the "stop" position. Usually, this is accomplished by using an additional set of contacts inside the kill switch to disable the ignition system. For example, if the extra set of contacts on the kill switch are used to interrupt power to the ignition coil, the engine will definitely stop. In the case of coil-on-plug engines, the same set of contacts can be used to defeat the relay supplying power to the DME or Motec, etc.
There are other techniques, including the use of the additional contacts in the kill switch to open a high-capacity relay connected between the alternator and the "hot" wiring. But it is usually easier to just disable whatever is providing spark to the engine.
There are other techniques, including the use of the additional contacts in the kill switch to open a high-capacity relay connected between the alternator and the "hot" wiring. But it is usually easier to just disable whatever is providing spark to the engine.
"18. An electrical cut-off switch, either externally mounted or with externally accessible pull wire - preferably on the driver’s side - is required. The location of the handle or pull must be indicated with the standard approved decal. The switch must disconnect the battery from all circuits except electrically operated on-board fire systems, and must shut off the engine while it is running well above idle speed. (See Appendix C)"
So I looked around at some other rule books, and most others have the same basic language (POC, BMWCCA, etc). The POC rule book even has a hand drawn picture that shows how to hook it up to the battery. Are these scantioning bodies all wrong?
02-02-2005, 06:26 PM
#3
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Originally Posted by Doug Donsbach
I'm not sure what you're trying to say, but how is what I wrote at odds with the rules you cite?
Btw, I just tried my disconnect (which is on the battery neg terminal) and it does in fact work, including at higher RPMs. It also is only capable of disconnecting one circuit, so I'm not sure how I'd wire it for multiple things (battery & coil, etc.)
02-02-2005, 06:38 PM
#4
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Originally Posted by Pesky 914
The rule seems to imply that you just need a disconnect on the battery.
Btw, I just tried my disconnect (which is on the battery neg terminal) and it does in fact work, including at higher RPMs. It also is only capable of disconnecting one circuit, so I'm not sure how I'd wire it for multiple things (battery & coil, etc.)
02-03-2005, 12:30 AM
#5
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Pesky you need to replace your switch with a multi-terminal switch, two big terminals like the one you've got and two/four smaller ones to cut the power to the coil and or fuel pump. A switch with only the two large terminals cuts the battery power but the alternator is still connected and as you take the battery out of the system voltage spikes can damage electrical components.
02-03-2005, 10:28 AM
#7
Three Wheelin'
Pesky, It is very hard on the engine and electronics to use the kill switch to shut the vehicle off. It is recomended to only use the kill switch in an emergency to avoid damage.
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02-03-2005, 10:05 PM
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If you are using a race engine without a working alt. or a alt. with no wiring connected to it the engine will stop if battery is disconnected. The positive battery cable goes to the starter term. ,the cable from the alt. also goes to the starter term. The blue wire(on every porsche) from the alt.(the exciter wire) goes to your light in the dash. Ods are if you turn your ignition switch on and the alt. light works ,the alt. should charge.(unless you have abad alt.) Therefore the cable from the alt. to starter term. will charge the battery. If the cable from the starter term. to the battery is disconnected the alt(that charges from 12 to 13.7 volts ) will keep the entire car running( via the cable from starter term. ) unless you have a heavy load (wipers headlights heater blower motor) .
02-04-2005, 12:06 AM
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Very interesting guys. So, can the PCA Club Racing kill switch be installed by a novice DIYer? My shop wants to charge me 4-5 hours for the install, which I think sounds pretty high, but I'm not an expert by any means.
I think it would be pretty easy to install the battery disconnect, but what about the other disconnect terminal on the switch. What should it be connected to: the alternator, DME, or what and how?
Any and all advice would be greatly appreciated as I would like to do this myself instead of paying someone else to do it.
Thanks,
SKip
I think it would be pretty easy to install the battery disconnect, but what about the other disconnect terminal on the switch. What should it be connected to: the alternator, DME, or what and how?
Any and all advice would be greatly appreciated as I would like to do this myself instead of paying someone else to do it.
Thanks,
SKip
02-04-2005, 02:16 PM
#10
Burning Brakes
I think that 4-5 hours is pretty reasonable, especially as they have to fabricate mounts and set up pull cables, etc.
On my 944, it came to about 5 hours, but that included having to modify the OG racing kit and try to route the pull switch so that it didn't break the windshield with the hood open.
The wiring is probably fairly straighforward, but it's all the little niggling details...
On my 944, it came to about 5 hours, but that included having to modify the OG racing kit and try to route the pull switch so that it didn't break the windshield with the hood open.
The wiring is probably fairly straighforward, but it's all the little niggling details...
02-04-2005, 04:04 PM
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Originally Posted by swftiii
Very interesting guys. So, can the PCA Club Racing kill switch be installed by a novice DIYer? My shop wants to charge me 4-5 hours for the install, which I think sounds pretty high, but I'm not an expert by any means.
02-04-2005, 04:17 PM
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Why would it be hard on the engine/electronics to use the kill switch? How is it different from shutting off the ignition switch?
As someone mentioned, you need a 2-pole switch so that you can disconnect the alternator also. I bought this one:
http://www.longacreracing.com/catalo...d=477&catid=14
In this setup you'd need to install the switch on the positive battery cable and the alternator output (+), and not on the grounds, because you can't disconnect the alternator from ground.
Like almost anything else, if you took the time and were careful, it shouldn't be a difficult job. The biggest problem is crimping your own leads for the battery + cable. If you don't have access to a good crimper, probably not a good DIY job. Hint though -- West Marine (boating) stores have a crimper in the store and they sell all different gauge wire, and teminals.
As someone mentioned, you need a 2-pole switch so that you can disconnect the alternator also. I bought this one:
http://www.longacreracing.com/catalo...d=477&catid=14
In this setup you'd need to install the switch on the positive battery cable and the alternator output (+), and not on the grounds, because you can't disconnect the alternator from ground.
Like almost anything else, if you took the time and were careful, it shouldn't be a difficult job. The biggest problem is crimping your own leads for the battery + cable. If you don't have access to a good crimper, probably not a good DIY job. Hint though -- West Marine (boating) stores have a crimper in the store and they sell all different gauge wire, and teminals.
02-04-2005, 05:05 PM
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Originally Posted by Darren
Why would it be hard on the engine/electronics to use the kill switch? How is it different from shutting off the ignition switch?
