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Kill Switch Recommendations


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I have heard from two separate teams of issues with kill switches draining charging systems or making there cars cut out sporadically and they traced it to the kill switch.

 

is it more of a wiring issue or a certain brand of kill switch causing the problems?

 

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We have had 2 or 3 kill switches die over the years.  It is usually from poor internal contact that wears the contacts in our experiences.

 

We use a 2 post now.  It seemed the 4 posts were the ones we had problems with.  

 

We carry a spare now.

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Just now, mender said:

Never heard of a kill switch itself causing issues but I have seen some odd ways of wiring a kill switch that led to problems.

 

2 post or 4 post?

 

 

I'm getting ready to order one. what is the difference between a 2 and 4 post?

 

it will be used in a bejing motor werkes car😊

 

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14 minutes ago, Racer7x said:

 

 

I'm getting ready to order one. what is the difference between a 2 and 4 post?

 

it will be used in a bejing motor werkes car😊

 

Get the 4 post. It has one circuit that is meant to interrupt the main battery power (big posts) and a second circuit to shut down the engine (small posts). 

 

The big circuit is typically rated at 1000 amps momentary and 200 amps continuous and the small circuit is 20 amps. Run the main battery cable from the positive post through the big circuit and the power to the ecu through the small circuit. When the switch is turned off, the power to the ecu is cut, the engine will shut off and the battery will be isolated from the rest of the car.

 

The test is to run the engine to 2500 rpm then shut off the kill switch; the engine has to shut off. If you wire it the way I suggest, it will shut off as required.

 

The problems I've seen are from wiring, not the switch. On cars that had a separate charging circuit (not controlled by the ECU) people would end up with a loop that keep power to the engine via the alternator even though the main battery lead had been interrupted, and as a result the engine would stay running. This was especially true when attempting to use a 2 post single circuit kill switch.

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On the NASCAR NCATS car, we went through two kill switches before I traced the circuit and found out why. 

 

The car started to slowly lose battery voltage during a practice session and it started breaking up at high rpm. Charged the battery and replaced the alternator, and that seemed to take care of it for qualifying but the small circuit failed completely during the race (of course!). We ended up replacing the battery to finish the race. I replaced the failed master after that race but it was only a few races later that the second one failed. The battery had been drained and we didn't have time to charge it (pre-race procedure was to hook up the battery charger but ...) so we bump started it and sent him out for practice and he immediately reported low voltage and breaking up again. Another kill switch and a fresh battery got us through the weekend, and tracing and correcting the wiring ended the kill switch failures.

 

The previous owners had wired the alternator charging lead through the 20 amp circuit, which slowly failed that circuit the first time, then when the alternator was supplying max amperage to recharge the battery the small circuit couldn't handle the amperage and burned out.

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We had a 4 post kill switch that I believe was a factory defect.  Our car would die randomly on track.  It might come back immediately and it might not.  It seemed like cycling the kill switch would usually keep it from happening multiple times in a row.  Then at Barber in December it got much worse.  We couldn't keep the car running for more than 5 minutes or so at a time.  Replaced the kill switch and the car made it through a track day at Barber with no issues.

 

That being said, I'm probably going to buy a solenoid kill switch for the next build.

 

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1 hour ago, zack_280 said:

We had a 4 post kill switch that I believe was a factory defect.  Our car would die randomly on track.  It might come back immediately and it might not.  It seemed like cycling the kill switch would usually keep it from happening multiple times in a row.  Then at Barber in December it got much worse.  We couldn't keep the car running for more than 5 minutes or so at a time.  Replaced the kill switch and the car made it through a track day at Barber with no issues.

 

That being said, I'm probably going to buy a solenoid kill switch for the next build.

 

 

We just bought a car with a solenoid kill switch, I dunno if I like it or not. PO told us if the battery is not fully charged the solenoid has issues turning on (i.e. Set without the battery tender for two or three days). I'm used to the big 4 post we have and that physical clunk when you turn it on, the toggle switch is a bit odd to me

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23 hours ago, Jab31169 said:

PO told us if the battery is not fully charged the solenoid has issues turning on (i.e. Set without the battery tender for two or three days).

Interesting.  I was thinking the solenoid switch would be nice to locate in the same area as the battery.  Eliminates running a large wire to the dash. 

 

This is the one in the kit Bimmerworld sells.  It says it picks up at 8VDC.  If your battery is that low, I doubt the car would start.

http://www.farnell.com/datasheets/190320.pdf?_ga=2.109905733.1142308438.1525365384-180645817.1525365384

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My understanding of this whole kill switch thing that RPW or Pegasus sells is if you kill the car with a kill switch you need a way to discharge the alternator or the surge can kill it.  There is a thread on here a few years ago that detailed that issue and describes the way to wire it up with a resistor that comes with the switch and discharges the alternator.

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Or put a switch in the field wire and shut that off before the engine-running test. That test and after a crash are the only times you should use the kill switch to shut off the engine.

 

If you have to use the kill switch in a crash, spiking the alternator would likely be the least of your worries.

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Yeah but people forget and it only takes one time to kill an alternator or as I have unfortunately found out two times. At least I suspect thats what happened.  In my case the resistor had twisted 180 degrees and the in and out were together creating a dead short.

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What I do is wire the alternator to the always hot side  where the battery wire is on the kill switch, so when I kill the switch the alternator can at least still discharge to the battery until it stops.

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32 minutes ago, Justin9 said:

What I do is wire the alternator to the always hot side  where the battery wire is on the kill switch, so when I kill the switch the alternator can at least still discharge to the battery until it stops.

Except that puts a main power lead from the battery to the engine compartment without any way of interrupting that in the event of a crash. The idea is to isolate the battery completely.

 

I haven't fried an alternator yet with running the ECU power wire through the small terminals. On my car the ECU controls the alternator so when the ECU shuts off the field also shuts off. I haven't checked for a spike but I don't think there will be one.

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