Kill switches?

[Ian Moone]

Okay spent way too much time trying to figure this out.

 

1)...2 pole or 4?

 

2)...Switch the positive or negative side?

 

3)...Solid state or old school mechanical?

 

4)...If one wanted to have 2 kill switches,would they be installed in series? One for the driver and one for the rescue crew accessible easily from the outside.

 

5)...Are you wiring in the alternator? If so does the kill switch need a diode?

 

6)...Does the ECU need some sort of protection?

 

7)...If no diode is required what does one do with the voltage that is generated after the switch is thrown to keep from burning up the alternator?

 

8)...Am I making this WAY more difficult then it needs to be?

 

I am way better at fabrication then electrical stuff,so if you are inclined to add a wiring diagram I'd really appreciate that.

 

Car I am installing this in? Miata.

 

Enlighten me please.

Edited November 21, 2018 by Ian Moone
content

[mender]

3 minutes ago, Ian Moone said:

Okay spent way too much time trying to figure this out.

 

2 pole or 4?

 

Switch the positive or negative side?

 

Solid state or old school mechanical?

 

If one wanted to have 2 kill switches,would they be installed in series? One for the driver and one for the rescue crew accessible easily from the outside.

 

Are you wiring in the alternator? If so does the kill switch need a diode?

 

Does the ECU need some sort of protection?

 

If no diode is required what does one do with the voltage that is generated after the switch is thrown to keep from burning up the alternator?

 

Am I making this WAY more difficult then it needs to be?

 

I am way better at fabrication then electrical stuff,so if you are inclined to add a wiring diagram I'd really appreciate that.

 

Car I am installing this in? Miata.

 

Enlighten me please.

1. 4 post

2. Positive

3. Mechanical

4. Series

5. Alternator field wire on the small posts, alternator output on the engine side of the big terminals

6. No.

7. Field wire shuts off the alternator output.

8. Maybe, but it'll be easier next time.

 

Miata:

 

Looks like the alternator is under PCM control so shutting off the PCM also shuts off the alternator. I would wire the PCM main power through the small terminals.

 

[LAMR2]

As an alternative to having two cutoff switches and running thick battery cable everywhere, you can have the switch near the driver and just run a cable pull to a second location. One switch, but two ways to flip it.

[Ray Franck]

Switch Must be mounted in the center of the driver area , center of the dash or console , within reach of the driver while belted in.

[Andrew D Johnson]

9 hours ago, Ian Moone said:

8)...Am I making this WAY more difficult then it needs to be?

 

On the 80/90s Honda and BMW cars I have mainly worked on, you don't need any diodes or ECU protection at all. Yea, you have to bring the Alternator back to the kill switch otherwise if you isolate the battery only the alternator will continue to power the car. 

I run a setup that is SUPER easy on the 2 pole kill switches. 

1) Run the battery and the alternator to one side. 

2) Run your 12VDC bus to the other side.

 

Done. 

Edited November 21, 2018 by red0

[TBone]

2 minutes ago, red0 said:

I run a setup that is SUPER easy on the 2 pole kill switches. 

1) Run the battery and the alternator to one side. 

2) Run your 12VDC bus to the other side.

 

Done. 

That's how I've always done it also. Never understood the need to make it so complicated.

[wvumtnbkr]

I run a 2 post.  Battery and alternator to 1 post.  All of the other electrical goes to the other post.

 

I figure that the battery can act as an expansion tank for the extra current from the alternator.

 

No alternator issues.  Maybe I'm lucky?

[Team Infiniti]

11 minutes ago, wvumtnbkr said:

Maybe I'm lucky?

Nope, this is the simplest, most hardy way.

 

Put a 100-150a fuse in that alt wire and call it done.

 

Yes I know mender is loosing hair over this method.

[Andrew D Johnson]

9 minutes ago, Team Infiniti said:

Nope, this is the simplest, most hardy way.

  

Put a 100-150a fuse in that alt wire and call it done.

  

Yes I know mender is loosing hair over this method.

 

The wire acts as a fuse, I don't know how many amps though. 

[Team Infiniti]

12 minutes ago, red0 said:

 

The wire acts as a fuse, I don't know how many amps though. 

Your right BUT I can tell you first hand, every little thing can either help or hurt....it is no fun sucking acrid in car smoke when you have a concussion.

 

Early days I had a unfused lighting circuit that got pinched in a bad crash,  it made a mess of the harness, everything is on a fuse now.

 

The little incorrectly done things we seldom mention that, when said publicly, may help someone make the right decision later.

Edited November 21, 2018 by Team Infiniti

[Andrew D Johnson]

5 minutes ago, Team Infiniti said:

Your right BUT I can tell you first hand, every little thing can either help or hurt....it is no fun sucking acrid in car smoke when you have a concussion.

  

Early days I had a unfused lighting circuit that got pinched in a bad crash,  it made a mess of the harness, everything is on a fuse now.

 

Once my sloppy wiring and lack of fuses saved @enginerd's motor. If the car didn't catch fire and force him to pit, he would have never known the water pump belt flew off the car over 20 minutes earlier. When we were replacing the wiring that burned, the team next to us pointed out how the air above the hood was extra wavy and when we got the electric going again we confirmed the temp gauge was pegged. On the video the car ran WOT for 19 minutes without water pump belt and with the temp gauge pegged.  

[enginerd]

19 minutes ago, red0 said:

 

Once my sloppy wiring and lack of fuses saved @enginerd's motor. If the car didn't catch fire and force him to pit, he would have never known the water pump belt flew off the car over 20 minutes earlier. When we were replacing the wiring that burned, the team next to us pointed out how the air above the hood was extra wavy and when we got the electric going again we confirmed the temp gauge was pegged. On the video the car ran WOT for 19 minutes without water pump belt and with the temp gauge pegged.  

It made for a funny video... swatting out flames with my right hand while driving the back straight straight at NCM. A pegged temp needle showing in the background...

16 minutes of no water pump and the engine survived. Good advertisement for m20 engines and Redline Race Oil.

[Wink]

So just a PSA, we ran into issues running the switch below. On our third race we started consistently popping alternators. The switch was not handling the output, and it was back feeding to the voltage regulator. Went through five alternators before we figured it out. Since then we have done to the much heavier duty Longacre switch and havent seen any problems. 

 

 

 

 

[mhr650]

46 minutes ago, Team Infiniti said:

Your right BUT I can tell you first hand, every little thing can either help or hurt....it is no fun sucking acrid in car smoke when you have a concussion.

 

Early days I had a unfused lighting circuit that got pinched in a bad crash,  it made a mess of the harness, everything is on a fuse now.

 

The little incorrectly done things we seldom mention that, when said publicly, may help someone make the right decision later.

 

I use a 100 amp trolling motor circuit breaker on the alternator output.

 

https://www.amazon.com/Bussmann-CB185-100-Type-Circuit-Breaker/dp/B00139FQSS/ref=sr_1_4?ie=UTF8&qid=1542813204&sr=8-4&keywords=100+amp+circuit+breaker+12v

[mender]

2 hours ago, Team Infiniti said:

Nope, this is the simplest, most hardy way.

 

Put a 100-150a fuse in that alt wire and call it done.

 

Yes I know mender is loosing hair over this method.

Fortunately I don't have much left anymore ... 

 

But really guys, wire it properly! Do it for safety!

[Rodger Coan-Burningham]

You guys are lucky that don't run a resistor to ground the output of the switch when you kill it.  I kept going through alternators, found the wire on my resistor to ground from the kill switch broken, fixed it no more issues.  Rob, I don't understand the comment that you figure the battery can act as an expansion for the alternator.  If you throw the kill switch, the alternator and all other electrical will be separated from the battery?

 

Edit:  Haven't we all had this same discussion previously?  Seems like I remember it was discussed in an earlier thread.  Man I hate getting old.

Edited November 24, 2018 by Burningham

[Ian]

12 hours ago, Burningham said:

You guys are lucky that don't run a resistor to ground the output of the switch when you kill it.  I kept going through alternators, found the wire on my resistor to ground from the kill switch broken, fixed it no more issues.  Rob, I don't understand the comment that you figure the battery can act as an expansion for the alternator.  If you throw the kill switch, the alternator and all other electrical will be separated from the battery?

 

Edit:  Haven't we all had this same discussion previously?  Seems like I remember it was discussed in an earlier thread.  Man I hate getting old.

 

Rob rob has it set up the same way I do.  Battery and Alternator on one side, everything else on the other.  When you throw the switch, the battery and alt are still connected to each other, but nothing else, so the engine shuts down.  Ecu is isolated from any voltage spikes, and the battery acts as a capacitor to absorb and residual alt output from engine rotation.

[mender]

12 hours ago, Burningham said:

 Rob, I don't understand the comment that you figure the battery can act as an expansion for the alternator.  If you throw the kill switch, the alternator and all other electrical will be separated from the battery?

 

It appears that many people have their master switch wired wrong:

On 11/21/2018 at 6:58 AM, wvumtnbkr said:

I run a 2 post.  Battery and alternator to 1 post.  All of the other electrical goes to the other post.

 

2 minutes ago, SonsOfIrony said:

Rob has it set up the same way I do.  Battery and Alternator on one side, everything else on the other.  When you throw the switch, the battery and alt are still connected to each other, but nothing else, so the engine shuts down.  Ecu is isolated from any voltage spikes, and the battery acts as a capacitor to absorb and residual alt output from engine rotation.

Etc, etc, etc. 

 

The correct way is to isolate the battery from the rest of the car as per 3.14.1 which states that both the main battery circuit (including the alternator output to the battery) and the ignition circuit must be interrupted by the kill switch. Attaching the alternator to the battery either directly or via the master switch terminal defeats one of the main purposes of the master switch, which is to eliminate battery power as a possible means of starting a fire or having the battery explode from a dead short.  

 

Next time you get ready to wire your master or are sitting on the grid waiting to go racing, look at your battery sitting just behind you and remember that it's a chemical grenade full of acid just waiting for the pin to be pulled. That plastic battery box will help contain some acid from a spill but certainly won't survive an explosion.

 

"I like to attach my racing harness with coat hangers, so much easier than using bolts."

 

[Rodger Coan-Burningham]

20 minutes ago, SonsOfIrony said:

 

Rob rob has it set up the same way I do.  Battery and Alternator on one side, everything else on the other.  When you throw the switch, the battery and alt are still connected to each other, but nothing else, so the engine shuts down.  Ecu is isolated from any voltage spikes, and the battery acts as a capacitor to absorb and residual alt output from engine rotation.

 

Would that not be in contrast to this sentence in 3.14.1?

 

"Both the main battery circuit and the ignition circuit must be interrupted by the kill switch."

 

Edit: Ok Mender beat me to it on the reply.

Edited November 24, 2018 by Burningham

[Rodger Coan-Burningham]

I also have a 150 amp circuit breaker directly after the battery positive post.  I just don't want to take a chance at a dead short in the battery cable.  Plus I run the cable in harness sheath to give it one more layer of protection.  

 

Edit: At first I had my battery mounted in the trunk to keep it away from me.  It felt like a pendulum with the weight behind the rear tires, so I thought about where the optimum placing would be and decided it might be best to separate the electrical source from the fuel as well as the weight issue.  Still not sure which is right, because now it sits behind the passenger area in a plastic box.  

Edited November 24, 2018 by Burningham

[mcoppola]

@Burningham I like the circuit breaker idea. 

I too don't understand why people would wire the battery and alternator to one side of the kill switch, thus always leaving the feed to the alt (and probably starter) as a hot wire. 

IMO Tech should use a test light at the alternator and starter to determine if your kill switch is truly wired to "interrupt the main battery circuit." If there's still voltage/power going anywhere past the kill switch it should automatically fail. 

Yes, I've heard all the arguments about how those of us that run 4 or 6 pole switches are complicating things - but I'd hate to have my car burn up because I didn't educate myself, or was too lazy or cheap, to wire in the kill switch the correct way, isolating the battery from anything further than the kill switch. 

Edited November 24, 2018 by mcoppola

[mender]

8 minutes ago, mcoppola said:

@Burningham I like the circuit breaker idea. 

I too don't understand why people would wire the battery and alternator to one side of the kill switch, thus always leaving the feed to the alt as a hot wire. 

IMO Tech should use a test light at the alternator and starter to determine if your kill switch is truly wired to "interrupt the main battery circuit." If there's still voltage/power going anywhere past the kill switch it should automatically fail. 

Yes, I've heard all the arguments about how those of us that run 4 or 6 pole switches are complicating things - but I'd hate to have my car burn up because I didn't educate myself, or was too lazy or cheap, to wire in the kill switch the correct way, isolating the battery from anything further than the kill switch. 

I was just thinking about a fictitious (or not) conversation between three racers about kill switches:

 

"I went for the simple method and wired the alternator output to the battery terminal on the master. Now I don't worry about voltage spikes."

"My starter was slow so I wired it to the battery terminal on the master. Now it cranks better."

"I saw what you guys were doing, combined the two and saved myself the cost of a master switch."

Edited November 24, 2018 by mender

[Racer28173]

To recap the rule and the posts above this one, one of the goals of the kill switch is to isolate the battery FROM EVERTHING ELSE.  You can’t get around having a cable run from the battery to the switch itself, but that cable run should be as short as reasonable and hopefully both protected and unlikely to get pinched in a crash.  The kill switch isn’t for turning the engine off, although some people choose to use it for that too because it performs that function if wired correctly. 

 

A buddy of mine had a car catch fire (no battery isolation switch) and the car started to “drive away” despite the fact that the engine was turned off.  It had a wiring diagram similar to the Miata above and the insulation on the starter solenoid wire melted off, grounded out, and engaged the starter.  By isolating EVERYTHING from the battery, we are avoiding that sort of situation.  If I were a safety worker coming to the aid of a driver in a wrecked/fiery/etc. car, I would want to be able to count on a minimal chance of the car starting to move, the battery exploding, etc.  

[Ian]

11 hours ago, mender said:

 

It appears that many people have their master switch wired wrong:

 

Etc, etc, etc. 

 

The correct way is to isolate the battery from the rest of the car as per 3.14.1 which states that both the main battery circuit (including the alternator output to the battery) and the ignition circuit must be interrupted by the kill switch. Attaching the alternator to the battery either directly or via the master switch terminal defeats one of the main purposes of the master switch, which is to eliminate battery power as a possible means of starting a fire or having the battery explode from a dead short.  

 

Next time you get ready to wire your master or are sitting on the grid waiting to go racing, look at your battery sitting just behind you and remember that it's a chemical grenade full of acid just waiting for the pin to be pulled. That plastic battery box will help contain some acid from a spill but certainly won't survive an explosion.

 

"I like to attach my racing harness with coat hangers, so much easier than using bolts."

 

 

You mean I'm going to have to re-wire my kill switch, and roll my fenders further this winter?  Y'all starting to sound like my wife.....

[Ian Moone]

Just great! A big debate and no definitive  answer as to the original questions. My bad for asking.