Thoughts on this Kill Switch?

[Ronzo_volvo_guy]

Surferboy;

You're absolutely correct...it was "Tully Mars" showing the relay he got...and because it was one with an internal snubber and wired in, not observing polarity, he experienced the PFFFT issue. This would NOT occur with no diode, but as I noted, it cannot hurt to have one...they do have a valid function! In any case, there is nothing wrong with the one relay circuit, and you can expect it to work reliably for a looong time!

Cheers

[Ronzo_volvo_guy]

Sodo:

"So you're saying that little coil sends out a voltage spike? [Absofreakinlutely! Every coil does...its SCIENCE! (T. Dolby)]
Yikes I had a big starter solenoid as a battery isolator for years.
I could FEEL it throw under the driver's seat.
Likely a much bigger coil than those little Bosch relays. [See more SCIENCE! below!]

Incidentally, this relay if used per the schematic....
the relay coil cannot spike the ECU, right?
Because the ignition is switched off at the time the relay is de-energized
ahem.......(key-tus interruptus Wink )"

Science: Interrupting the current in ANY coil, be it a cute little relay like this or the Primary of your Ignition Coil, or a mongo contactor like a Starter Solenoid, the science and physics say that the collapsing magnetic field WILL/MUST generate such a spike...the bigger the coil, the more energy has been stored (magnetically), and the bigger the reverse spike WILL be as it collapses...and it WILL always occur across the contact which is breaking the current...often it is not an issue because switches and internal contacts are selected such that this spike, and the resulting plasma and associated contact erosion occurring at the contact is low enough so that the system can have a long service life, but in places where there are more critical things in play (like at your old school Ignition Points), where timing is also rather important, a "Condenser" is used to help minimize the plasma and keep the contact erosion (and accompanying change in timing) down.**

Again; The tiny relay coil doesn't store much energy at all, but a spike will occur (OK it won't have much "area under the curve"), but snubber diodes can never hurt, and with sensitive electronics on-board, as cheap as they are, it can never be a bad idea to include them to keep voltage spikes down.

Cheers

Edit/Added: ** In more modern Ign Sys, where there are electronics (actually a big transistor) instead of contact "Points" doing the Primary current control, it too will be subjected to the spike as it breaks the Coil current, so MUST be 1. selected at time of design to be capable of handling the hit itself, or 2. be additionally protected with a snubber component or network, or 3. or BOTH (belt and suspenders!), since Ign is a "Mission Critical Function" the failure of which must be avoided pretty strictly!

[goubeaux]

[the joker]

you just gave the keys to the thief's with your diagram

[Ronzo_volvo_guy]

Joker;

...not if the Momentary Switch is "discretely located"!

[the joker]

exactly look into summit racing ground killer switch with red plastic key,

[DanHoug]

i so want to build a 20kV seat shocker, wired simply with a bypass switch and powered by the ignition on. but i know i'd forget the switch and zap myself or much much worse, my wife. so it needs a time delay circuit and an imbedded MP3 player announcing "Electrocution in 10 seconds" to give me time to hit the bypass.

only about $40 of parts for the MP3 appliance and 12v HV source. a little LED display of the time countdown would add to the drama.
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[1988M5]

85 and 86 are connected backwards. 86 is control power input, 85 is the ground to complete the circuit to energize the coil pulling the high amp contacts together.

BK
_________________
1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs.

[goubeaux]

1988M5,

Thanks for pointing that out.
-BTW This is NOT my diagram, and is (one of several revs) part of this thread, that's been around for 2+ years now.

My neighbors Vanagon was stolen a few weeks ago, so my renewed interest in a viable kill switch has been re-kindled !

-john

[the joker]

Long time ago 1970's drove a AMC Javelin, for auto dealer, had to lift you ass off the seat , to start it, kill was a pressure pad this auto was worth sealing deck out for track racing fast

[VicVan]

[goubeaux]

Guys, I am implementing the below Kill switch setup, and have everything in place.

I'm using "key in power" via the SU lead on the ign switch.
I've tested that I am getting 12V when key is barely inserted.
Checked and dbl checked the connections, pin numbers solder joints on my wiring.

I'm stumped, as I'm getting the following behavior:

Upon inserting key in ign I hear the relay click, without even hitting the momentary switch. FP IS getting ground as well. Engine gets fuel and starts.
I've disconnected the GND on the momentary switch thinking that it might have failed closed, and I get the same behavior, as IF it is not even being used. I've swapped relay connections on 85 and 86 as someone suggested in this thread that they are wrong on the diagram. Still same behavior. I've tried a 2nd relay of the same type ( they came in a 2 pack ) same behavior.

At this point I'm thinking I have made some simple mistake ( embarrassing if so ) OR maybe I have the wrong type of relay or maybe it's faulty, OR ? Here's where my limited electronics skill comes into play.
I appreciate any ideas .

here's the relay I'm using:
https://www.amazon.com/gp/product/B08BHR2RM7/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

[ImAddicted]

Are you wiring to 87 or 87a?
_________________
1979 Transporter (sold)
KC1MUR

[spitsnrovers]

The way I see it is - your momentary switch and the key-in switch are in parallel. Therefore either one being activated will activate the relay.
_________________
'88 VW Westfalia
'75 Triumph Spitfire 1500

[goubeaux]

To answer Qs: I AM wiring to 87 on relay -just as in diagram.

Also, what puzzles me Is that numerous posters (in this thread) have said that this very wiring plan DOES work, and that they have used it with No issues...

Yet <spitsnrovers> I get your point, and with my basic understanding I too wondered how the two ground paths differ But maybe you are not clear on how the setup is supposed to work.

My understanding is that the activation of the momentary switch creates the GND path for the 12V the key in provides thus activating the relay.

[fxr]

Are you sure your momentary switch is a NO normally open one, rather than an NC normally closed? Both are readily available, and can get muddled up if you're not careful.
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[goubeaux]

<fxr> Thanks, Yes, that dawned on me.
To be clear I do want a NC switch ?

I checked the switches I bought are listed as "normally open"
I also tested the one I installed with a meter ahead of time.

With that in mind i removed the gnd connection on the momentary switch end and as noted the relay still activates and latches.

TWTADE/6Pcs Momentary Mini Push Button Switch 1A 250V AC 2 Pin SPST NO (Normally Open) with line PBS-110-X-6S
https://www.amazon.com/gp/product/B07X1PDLM8/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

[goubeaux]

Heres' the switch you indicated you had used in your setup, and it worked, in the other thread:

https://www.amazon.com/gp/product/B0752RMB7Q

Cylewet 12Pcs 1A 250V AC 2 Pins SPST Momentary Mini Push Button Switch Normal Open (Pack of 12) CYT1078

This looks identical to what I used ?

[goubeaux]

I might have found what's causing the behavior I'm seeing.
In my haste to test the setup I just stripped the new ground wire at the FP and wrapped it around the negative terminal without a crimped eyelet terminal, IF it was grounding somehow on the pump this would explain things.

I removed the wire all together from the FP negative terminal then tested the relay and momentary switch up front. The relay latches as it should - key in AND touching the momentary switch.

Now back to properly grounding the wire at the FP terminal.
Crossing my fingers....

[goubeaux]

Well that was not the issue, ie grounding at the FP.
My momentary switch IS a (NO) normally open one too.
I've swapped out with a different relay ( one with just an 87 and NO 87A pin) - no change, (a SPST relay)

I'm still stumped on how the relay is getting ground and latching IF I do not press the momentary button switch but just insert the key?