Technical Battery kill switch idea

Better still leave the alternator hooked up and run electronic ignition [ It'll make more power with a continuous 14 volts being fed into it ]
An alternator only robs power if you have a flat battery, or constantly draining the electrical system.
The internal regulator is the only cut-out switch you need

 

The 'kill' switch needs to be on the positive cable - per NHRA, including the bold type.
A solenoid (we use Standard Ignition SS608) is the preferred method as disconnecting means, they're located in the passenger foot well along with the ignition & electronics package. That solenoid needs both a hot and ground wire to engage, the hot will come from the disconnect switch located at the 'rearmost righthand corner' of the racecar and I add another kill switch for the driver so he can disconnect the ground, or you can just give it a permant ground (if your driver is ever upside down he'll appreciate the kill switch so's he can turn the electrical off).
The battery and altenater connect to the 'line' side of the solenoid; fuse panel, ignition etc connect to the 'load' side, with engine running and if either kill switch is turned 'off' the cars' electric and ignition are isolated from the battery, the altenator sends power only to the battery and the engine will shut off.
Back in the early 80's we'd weld a tab in the rear and bolt one lug of a typical disconnect switch to the tab, run a ground wire from the battery to the other lug and send a handle from the switch outside the car, very simple and clean. It disconnected the ground, the wording was that the car needed a positve disconnecting means and that method complied witht he rules - kinda. It was lateish eighties they changed the wording to bold print on the positive to clarify the intent to mean +12v cable. Just a little history.

 

That's cool oj! So can the solenoid be under the hood? Or does it have to be a certain distance from the battery?

 

I hope you use a normally open relay so that in the event of a crash and the control wire is broken then the solenoid will open.

 

All NHRA tech we have ever been thru requires it to be on the POSITIVE side- on the rear of the car and marked ON-OFF
If your using a push-pull method, they seem to prefer the pull-on push-off
SPEEDY

 

Yes , a 1.23 - 60 foot will possibly throw the switch out on launch of the trans break .Always want pull out to activate push in to kill .

 

Yes, for years many pro builders put them on the firewall. People saw them and thought they were for the starter, so they copycatted it without knowing why. Theres' tons of cars out there with a solenoid on the firewall to operate the solenoid on the starter - bad juju.
The real intent of the solenoid is to shorten the altenator charging circuit. An altenator will put out at least 14.5 volts (race altenators put out 18ish) and you want all of that going to the ignition system. If your disconnecting means is at the rear of the car then the altenator output has to travel all the way back to the battery and then run up to the front and ignition - major voltage drop. By locating the solenoid between the altenator and ignition you'll have a major advantage with hotter ignition spark, the entire altenator output is with a couple feet of its' source and enduse. I've seen a lot of ignition systems up front on prostock and top sportsman to make it as short as possible. Some of the ignition systems I've tested will draw near 30amps - the coil wire will be hot to the touch - and the higher the supply voltage the happier the ignition system is.

 

If you run an alternator cut off relay, make sure it's a beefy one. 80 amp alternator, means a bigger relay than 80 amps, etc.


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