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Nick83
Samba Member
Joined: July 10, 2018
Posts: 63
Location: Seattle, WA
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 Posted: Thu Sep 13, 2018 2:33 pm Post subject: Thoughts on this Kill Switch? |
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I'd like to add a kill-switch to my van for security. My goal is mainly slowing down a thief while keep modifications to the stock systems to a minimum (i.e. it should be easy to revert) and idiot-proof (i.e. I don't have to remember to flip the switch off every time I leave the van.)
I'm not terribly experienced with 12v wiring, but I came up with this and was wondering if anyone sees an obvious mistakes:
Basically, I'd replace the body ground on the fuel pump with a new wire run to the fuse-box area. In a pinch, I could yank that wire from the relay and body ground it to bypass the system, but your average thief probably wouldn't realize that for a bit.
What I'm expecting to happen:
When the key is inserted, the fuel pump is ungrounded. Pressing the switch momentarily grounds the first relay's coil, causing it to close and ground itself and the second relay which in turn grounds the fuel pump. The system remains functional until the key is removed from the van and the grounds are broken. |
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dobryan
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Joined: March 24, 2006
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Location: Brookeville, MD
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Nick83
Samba Member
Joined: July 10, 2018
Posts: 63
Location: Seattle, WA
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| Posted: Thu Sep 13, 2018 3:30 pm Post subject: Re: Thoughts on this Kill Switch? |
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| dobryan wrote: |
FWIW I am not fond of a kill switch that disables
the fuel pump. If it malfunctions it can leave you stranded in a dangerous circumstance. A kill switch that disables
the starter solenoid is safer imho. |
Are you suggesting it could cut out while driving or would leave you stranded? I guess I'm not seeing how you'd be any less stranded with a malfunctioning starter. |
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calo1956
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Joined: April 18, 2011
Posts: 701
Location: long Island new york
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| Posted: Thu Sep 13, 2018 4:03 pm Post subject: Re: Thoughts on this Kill Switch? |
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i had a kill switch wired on the hot side of the fuel pump when my van was new, had it for years, never had a problem, actually thinking of adding it back again...
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Nick83
Samba Member
Joined: July 10, 2018
Posts: 63
Location: Seattle, WA
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| Posted: Thu Sep 13, 2018 4:11 pm Post subject: Re: Thoughts on this Kill Switch? |
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| calo1956 wrote: |
| i had a kill switch wired on the hot side of the fuel pump |
Would you choose the hot side again? That was my first design but I thought running one new ground wire would be less troublesome than going from the pump to panel and back with the hot side. I'm assuming I can't tap into the hot directly at the fuse panel and would be splicing in at the pump. |
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Ahwahnee
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Joined: June 05, 2010
Posts: 9810
Location: Mt Lemmon, AZ
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| Posted: Thu Sep 13, 2018 4:18 pm Post subject: Re: Thoughts on this Kill Switch? |
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Switching the ground is how I did mine - I agree it is a simpler approach. If something goes worng I still have the old ground wire there by the pump and can reconnect it in seconds.
What I do not see is how the fuel pump continues to operate when the momentary switch is released - seems like bith relays would open.
BTW - I did not use any relay, just a basic switch - has been no problem in the years I have used it. |
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dobryan
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Joined: March 24, 2006
Posts: 16504
Location: Brookeville, MD
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| Posted: Thu Sep 13, 2018 4:22 pm Post subject: Re: Thoughts on this Kill Switch? |
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| Nick83 wrote: |
| dobryan wrote: |
FWIW I am not fond of a kill switch that disables
the fuel pump. If it malfunctions it can leave you stranded in a dangerous circumstance. A kill switch that disables
the starter solenoid is safer imho. |
Are you suggesting it could cut out while driving or would leave you stranded? I guess I'm not seeing how you'd be any less stranded with a malfunctioning starter. |
Correct it could cut the power to the fuel pump while
driving.
A malfunctioning kill switch to the starter solenoid just won’t let the starter work. Still safe where you parked it last. You could then bypass
the kill switch since you know
how and be on your way. Much safer imo.
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'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD
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chompy
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Joined: August 12, 2014
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Location: Cascade Locks
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| Posted: Thu Sep 13, 2018 4:27 pm Post subject: Re: Thoughts on this Kill Switch? |
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Don't put a switch on the hot wire, use the ground wire. You don't really need a relay either, like Ahwahnee said.
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Nick83
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Joined: July 10, 2018
Posts: 63
Location: Seattle, WA
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| Posted: Thu Sep 13, 2018 4:38 pm Post subject: Re: Thoughts on this Kill Switch? |
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| Ahwahnee wrote: |
| What I do not see is how the fuel pump continues to operate when the momentary switch is released - seems like bith relays would open. |
The coil in relay 1 has power but no path to ground; pressing the momentary switch provides a path to ground, causing the relay to close. This provides an alternate ground for both relay 1 and relay 2, which means both relays should stay engaged until power is cut.
At least I think that's what happens... this is my first experience working with relays and I've only done a small amount of DC otherwise, so I could be way off base somewhere. |
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Nick83
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Joined: July 10, 2018
Posts: 63
Location: Seattle, WA
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| Posted: Thu Sep 13, 2018 4:44 pm Post subject: Re: Thoughts on this Kill Switch? |
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| chompy wrote: |
| You don't really need a relay either, like Ahwahnee said. |
I know I could just use a standard switch, but I don't want to have to remember to flip a switch back to the off position in order to make it effective. Unless someone sells a specialty switch that can auto-reset or something? |
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chompy
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Posts: 400
Location: Cascade Locks
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| Posted: Thu Sep 13, 2018 5:20 pm Post subject: Re: Thoughts on this Kill Switch? |
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| Nick83 wrote: |
| chompy wrote: |
| You don't really need a relay either, like Ahwahnee said. |
I know I could just use a standard switch, but I don't want to have to remember to flip a switch back to the off position in order to make it effective. Unless someone sells a specialty switch that can auto-reset or something? |
For my neighborhood I preferred a switch since vehicles are usually stolen with keys or screw drivers put in the ignition which seems like your system wouldn't prevent.
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calo1956
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Location: long Island new york
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| Posted: Thu Sep 13, 2018 5:41 pm Post subject: Re: Thoughts on this Kill Switch? |
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So based on using a simple toggle switch like i had for years, why is it preferable to put the switch on the ground vers the positive? I had mine on the pos and am thinking of putting it back, should i put it on the ground instead, and why?
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Ahwahnee
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Joined: June 05, 2010
Posts: 9810
Location: Mt Lemmon, AZ
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| Posted: Thu Sep 13, 2018 5:51 pm Post subject: Re: Thoughts on this Kill Switch? |
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| calo1956 wrote: |
| ...why is it preferable to put the switch on the ground vers the positive?... |
Probably not a lot of difference - but consider what happens if the run of wire chafes thru and touches metal somewhere along the way from the pump to the switch.
If it is a hot wire then you get a short, possibly smoke & sparks. And you should probably have a fuse on that line.
If it is a ground wire then all that would happen is your switch would not reliably turn off the pump. |
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Sir Sam
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| Posted: Thu Sep 13, 2018 5:56 pm Post subject: Re: Thoughts on this Kill Switch? |
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| chompy wrote: |
| Nick83 wrote: |
| chompy wrote: |
| You don't really need a relay either, like Ahwahnee said. |
I know I could just use a standard switch, but I don't want to have to remember to flip a switch back to the off position in order to make it effective. Unless someone sells a specialty switch that can auto-reset or something? |
For my neighborhood I preferred a switch since vehicles are usually stolen with keys or screw drivers put in the ignition which seems like your system wouldn't prevent. |
His system would assuming the would be thief doesn't see the momentary push button.
He gets in, puts the key in, turns it to on, presses the momentary switch which then latches the relays on to provide constant power to the fuel pump untill the key is turned off, then turns the key to start it, drives, stops, turns the key off and then when the key is off the relays turn off and the fuel pump has no more ground to run.
To the OP, I think this will work fine. What you have created here is a latching relay setup with the reset being the loss of power from the keyed hot power.
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Nick83
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Posts: 63
Location: Seattle, WA
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| Posted: Thu Sep 13, 2018 5:57 pm Post subject: Re: Thoughts on this Kill Switch? |
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| chompy wrote: |
| For my neighborhood I preferred a switch since vehicles are usually stolen with keys or screw drivers put in the ignition which seems like your system wouldn't prevent. |
True, you could get key-in power by jamming something in there, but it's still a switch you'd have to find. |
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calo1956
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Location: long Island new york
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| Posted: Thu Sep 13, 2018 6:10 pm Post subject: Re: Thoughts on this Kill Switch? |
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Thanks Ahwahnee, point well taken...
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dobryan
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bsrad
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| Posted: Thu Sep 13, 2018 7:20 pm Post subject: Re: Thoughts on this Kill Switch? |
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| dobryan wrote: |
| So you can do the same kill switch set up to the starter solenoid and never worry about a failure while driving... why is it better to cut off the fuel pump? Just trying to understand. |
I have no idea which is better, but I have the starter solenoid kill switch on my FJ40 and a ground fuel pump switch on my vanagon. I do get concerned with the landcruiser that it can be bump started and driven away where the vanagon can not.
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fxr
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| Posted: Thu Sep 13, 2018 7:22 pm Post subject: Re: Thoughts on this Kill Switch? |
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'They' could still push-start the van if just the starter was non-op. There are already plenty of single points of failure in the fuel pump circuit - one more won't hurt, plus it's probably easier to completely bypass by the owner that did that mod.
I chose to use a fuel-pump kill switch - but although the convenience of the OP's circuit may seem appealing, I prefer my hidden ON-OFF relay control switch (which needs a door to be open to operate) to the momentary switch which I presume is inside the cabin.
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wcdennis
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| Posted: Thu Sep 13, 2018 8:06 pm Post subject: Re: Thoughts on this Kill Switch? |
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The problem I see, is that the fuel pump is supposed to be energized when you first turn the key--this is to pressurize the fuel rail. It is a timed event and if you don't push your relay button at the same time you turn the key, you may not get enough pressure in the line to get the engine started. You might do better to use this circuit cut power to the coil instead.
One more thing: your circuit would work exactly the same with ONE double pole single throw relay. |
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