Topic: 2 second delay with master kill switch

https://youtu.be/1tojI4yHAIo

I have the car wired on a 2 prong master kill switch. The battery and alternator go to terminal A, everything that requires power goes to terminal B. This way you throw the switch and all source of power are disconnected from all loads. The problem is when the car is running, you throw the kill switch and it takes about a second or 2 before the HEI finally discharges it's capacitance and shuts the car off. It's repeatable and turns off everytime, but I don't know how to make it instant. Will tech fail me for this?

Video shows instant off with the ignition switch, but a delay with the master kill. The instant off is a little hard to hear because the fan was running.

Re: 2 second delay with master kill switch

I actually think I figured out my problem. When I shut the car off at the ignition switch, ignition relay opens, engine dies. When I shut the car off with the master kill switch, all relays stay closed, engine dies when voltage drops below HEI threshold. I just noticed this issue today and the only thing different was that I plugged the fan in. An electric motor becomes a generator when it's free spinning.  So the car stays running until the electric fan slows down and stops generating enough voltage, then the engine dies. Can anyone suggest a way to isolate the fan from both the power and load side of the switch? Will tech pass me knowing there's a 2 second fan power down delay?

Re: 2 second delay with master kill switch

I think tech will fail you on this, but an email to Evil John will be your best bet.

All you need to do is have your fan powered by a source that is not on the same circuit with your ignition.  As long as it is in a separate circuit, it will not feed the ignition when you turn off the disconnect.

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4 (edited by Drdanteiii 2016-07-26 05:37 AM)

Re: 2 second delay with master kill switch

I'd add a relay to the fan or the HEI so that one is isolated when the master is thrown.

Other option would be a diode in the fan wiring to prevent back feed.

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Re: 2 second delay with master kill switch

We had the same issue after going from a small after market fan to a bigger fan from a 4th gen Camero. The engine ran on a bit and the ignition switch got hot to the point of failure shutting the engine off. The fan is now on a separate switch with a relay, not ideal in case anyone forgets to switch it on but good for the cold mornings when you want the engine up to temperature quickly.

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6 (edited by jrbe 2016-07-26 02:12 PM)

Re: 2 second delay with master kill switch

Problem is that it's back feeding power in and
keeping the relays on. While the relay is on it back feeds and the relay can't let go. Adding a relay won't help unless it's on its own leg of the kill switch, at that point, just run the coil + relay power through its own part of the kill switch (multi switch kill switch.) For what it's worth a fuel pump or other "generators" can back feed power into the system too.

Realize electricity goes where it can. Just because you add a relay doesn't mean it can't be back fed. Diodes can sometimes help but aren't always the answer. A diode in the fan power will be huge and could do funky new things with voltage spikes.

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Re: 2 second delay with master kill switch

jrbe wrote:

Problem is that it's back feeding power in and
keeping the relays on. While the relay is on it back feeds and the relay can't let go. Adding a relay won't help unless it's on its own leg of the kill switch, at that point, just run the coil + relay power through its own part of the kill switch (multi switch kill switch.) For what it's worth a fuel pump or other "generators" can back feed power into the system too.

Realize electricity goes where it can. Just because you add a relay doesn't mean it can't be back fed. Diodes can sometimes help but aren't always the answer. A diode in the fan power will be huge and could do funky new things with voltage spikes.

Agree. I though about a diode, but one that can handle the 50 amps of inrush current would be huge. I think stepping up to a 4 pole switch and putting the fan on one circuit and the rest of the car on the other will prevent the backfeeding. While other electronics like fuel pump can backfeed, only the fan has enough momentum and power to keep the car running.

Re: 2 second delay with master kill switch

Try putting the fan with the battery and alternator. That way, it is isolated from the ignition after you switch it off.

Re: 2 second delay with master kill switch

I'm not looking at getting into the debate about what cutting all power means. So that aside...

If you do decide to put the fan on the battery side of the switch you have to make sure the relay coil side is either all on the switched side or the battery side to once again prevent back feeding power. I wouldn't do it, I've had fans melt down factory wiring a few times. I'd much rather have the kill switch be able to kill everything. Just my preference.

The other strange thing about the fan keeping the engine running is when you're at speed, airflow through the front can turn the fan into a windmill. It may not shut off at all with the kill switch at speed when it's doing this 2 second delay parked.

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Re: 2 second delay with master kill switch

If you turn the key off, does the car shut off immediately?

If the answer is yes, get one of these kill switches. It has extra posts that you wire your ignition into and it acts like you've turned the key.
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Re: 2 second delay with master kill switch

TheEngineer wrote:

If you turn the key off, does the car shut off immediately?

If the answer is yes, get one of these kill switches. It has extra posts that you wire your ignition into and it acts like you've turned the key.
https://www.pegasusautoracing.com/produ … RecID=1464

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Re: 2 second delay with master kill switch

I ended up with one of these cuz it was a spare in a teammates trailer:
http://www.frsport.com/Battery-Switch_p … gQodzGYFIQ

Put the battery and alternator on one post, all the major loads on the other. The ignition relay switch power goes through a set of terminals so when you throw the switch, it opens the relay and cuts off the ignition. Opening the relay stops the backfeeding from the fan while it spins down so it now shuts off instantly.

Re: 2 second delay with master kill switch

If you put the battery and alternator on the same post won't you just be connecting your battery straight to ground through a resistor when you turn the switch off?

I thought you put the alternator on the "out" side not the "In" side so when you run the jump line it's from the "out" through the W circuit to the resistor to ground causing a controlled dump of the charge still banging around with nowhere else to go except through the Voltage regulator.

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14 (edited by jrbe 2016-07-29 10:04 AM)

Re: 2 second delay with master kill switch

It depends on how you wire it and if you use the included load dump resistor or not. If the alt is with the battery on the switch leg and never cuts it from the battery it won't have load dump issues and doesn't need the resister. but the switch won't cut power to the alt. It's a debate I'm not interested in arguing, my preference is to have it kill power to the alt when off.

If you wire it as the directions show you get all of the benefits of using a 6 pole switch. You can wire it other ways but you could be bypassing safety to a point and or some functionality you paid for. I don't understand paying for the $ switch and bypassing functionality.

There are other racing leagues that require power be cut to the alt when the switch is off. If you're considering other leagues and buying the $ 6 pole switch, wire it as the instructions show and don't worry about kill switch funkyness anymore.

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Re: 2 second delay with master kill switch

Only if I actually installed the resistor to ground. That's there to give your system somewhere nice to dump the extra voltage when you cut the switch. Since this isn't a daily driver and we'll likely only throw that switch with the car running a handful of times, I'm not too worries about it frying anything. Its also wired to run the fan all the time, so when we do throw the switch were using the fan as the voltage dump instead of installing the resistor.

On a 2 post switch, you either run the alternator to the battery side or the load side. If you run it on the load side, you're not actually cutting all the sources of power. So in a situation where your ignition relay goes bad and fails on, cutting the master kill switch won't turn your car off as the alternator will be feeding it still. So running the alternator on the battery side is rougher on the system, but safer if you need to use the switch in anger.

Re: 2 second delay with master kill switch

Hi,

Not installing the resistor because you'll only use your kill switch a few times seems like a rediculous proposition to me.  You will use it every time you go through tech, every time you get a black flag and your driver is too flustered to turn the key switch off (%93 according to my experience), every time the exhausted driver coming in for fuel isn't fast enough for the anxious driver going in (%50) and then every time when your crappy ignition switch fails (now %100 for us).  It's 15 minutes now and will save much more time when you should be racing.  On top of that your alternator may not be able to take the spike once. 

That said the resistor that came with our expensive switch was not meant for an automotive environment.  Less than 5 races and the leads fatigued and broke.  We used the HVAC fan resistor.  It is rated for the vibration of an automotive environment and free!

Good luck!

Sam

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Re: 2 second delay with master kill switch

agent4573 wrote:

https://youtu.be/1tojI4yHAIo

I have the car wired on a 2 prong master kill switch. The battery and alternator go to terminal A, everything that requires power goes to terminal B. This way you throw the switch and all source of power are disconnected from all loads.

.

Hmmm.
Just so we're on the same page:  The point of the kill switch is to do one thing, de-energize the entire vehicle.  It normally does this with a big DPST switch.  One pole is a high-amp switch to disconnect the battery from the rest of the car.  The other pole is a lower amp switch to disconnect the alternator's regulator from its power supply so that the rotor is de-energized and its magnetic field will collapse and no longer induce the field coils to produce juice.  So when the kill switch is thrown, the car has no available source of electricity.  The kill switch is supposed to be used on the sources of electricity and completely ignores the users of that electricity including the ignition, fan and lighted dingle balls around the dash.

Your description of how you wired your switch sounds incorrect.  It sounds like you have the BAT terminal on the alternator grouped with the battery.  Is that correct?  If so, depending on where the battery and alternator connect to the rest of the vehicle.  It can work, but it ain't right. 

And if it is indeed wired this way and the rest of the electrical system is routed through the second pole, the second switch might not be rated to supply the entire rest of the electrical system unless it is one of the hi-amp DPSTs made for systems with one-wire alternators.  And in the case of a one-wire alternator, the battery and the alternator use the different poles of the switch.

If I am mistaken and you have it wired correctly, I believe this is a non-issue.  Ours goes on about a second or so this and has passed tech the first tech guy that saw it work even said, "Perfect."

When wired correctly, and the switch is thrown, the alternator's rotor core has residual magnetism that takes a moment or two to decay enough not to energize the field coils and continue to making electricity happen.

It takes a fair amount of current to run an ignition system, and that current goes up with RPM.  Try elevating your RPM before your turn off the engine.  See if that shortens the delay.  At tech they always ask you to run the engine up to 2000-2500 RPM.

And, as a practical matter, if it runs no more than two seconds, then whatever emergency you are using the kill switch for is not going to get much worse.

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18 (edited by kakarot1232001 2016-08-05 05:22 PM)

Re: 2 second delay with master kill switch

my clanker uses 6 pole switch.
the main high amp poles (3/8") connect battery to everything else. Think its rated at 250amp or something.
the other pole that connected same time as main poles connected to field wire of the alternator, simply interrupts it. think this one is 30 amp.
could also connect the other pole that is on when main is off through resistor to ground, but so far no used.

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Re: 2 second delay with master kill switch

When a magnetic field collapses it makes a voltage spike.  Voltage spikes kill diodes and electronics in general. For reference, a starter solenoid can make a spike of 80 volts when it lets go.  A collapsing field is also how ignition coils make spark.

Cooling fans can pull 20 to almost 100 amps when fully on. That's quite a bit of generated power while it's spinning down.

A lot of regulators are internal and get their power directly from the main alt to battery cable - not always easy to interrupt it there.

The 6 pole switch is the way to go to give the best chance of shutting it down and killing power between the alt and battery. There are other ways to do it of course too. It's definitely my preferred method.

-Killer B's (as in rally) '84 4000Q 4.2V8. Audis never win?

Re: 2 second delay with master kill switch

agent4573 wrote:
jrbe wrote:

Problem is that it's back feeding power in and
keeping the relays on. While the relay is on it back feeds and the relay can't let go. Adding a relay won't help unless it's on its own leg of the kill switch, at that point, just run the coil + relay power through its own part of the kill switch (multi switch kill switch.) For what it's worth a fuel pump or other "generators" can back feed power into the system too.

Realize electricity goes where it can. Just because you add a relay doesn't mean it can't be back fed. Diodes can sometimes help but aren't always the answer. A diode in the fan power will be huge and could do funky new things with voltage spikes.

Agree. I though about a diode, but one that can handle the 50 amps of inrush current would be huge. I think stepping up to a 4 pole switch and putting the fan on one circuit and the rest of the car on the other will prevent the backfeeding. While other electronics like fuel pump can backfeed, only the fan has enough momentum and power to keep the car running.


We have been failed for this before so you need to get it resolved. We ended up going to a 4 pole switch because of the fans backfeeding and keeping the car running longer than it should.

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