Thoughts on this Kill Switch?

[crazyvwvanman]

The ignition switch key-in pin is labeled SU in that diagram. When the key is inserted the switch connects power to pin SU. It has a very small wire and is not made for doing much work. You may really want a key-on power connection which is pin 15 on the switch.

Mark

[Tully Mars]

Hello Folks,

Well I am getting this done this weekend.

I am wondering if anyone can offer some advice on routing to the new ground wire to the relay and momentary switch from the fuel pump. I am mounting both in the dash/radio area.

Thanks in advance...
_________________
I'm a man. But I can change.
If I have to.
I guess.
_______
84 Wolfsburg Westfalia
Hobie Cow

[Tully Mars]

Well Crap...

I finally got the wiring done with the exception of the final hookup of the ground from the fuel pump.

So I went to test the operation of the relay but instead of a reassuring "click" I got a puff of smoke. Yikes..

Checked all my connections and I am 99 and 44/100% sure I have it right.

So... maybe a defective relay?
_________________
I'm a man. But I can change.
If I have to.
I guess.
_______
84 Wolfsburg Westfalia
Hobie Cow

[VicVan]

The puff of smoke came from the relay itself? When you pushed the magic button, or when you started to crank?
_________________
'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[Tully Mars]

[dobryan]

[Tully Mars]

[Surferboy120]

[Sodo]

[Surferboy120]

[fxr]

[Surferboy120]

[Sodo]

[Ronzo_volvo_guy]

Forum;

I am new around here and just posted an introduction, but as I am interested to add some sort of anti-theft measure to my son's Westy, I read the entire thread (and I am qualified to make technical comments just in case anyone's wondering, no bragging intended!)....

The single relay solution posted by OP is electrically sound, and while reading through the thread I did notice that the relay Surferboy procured for this has an internal snubbing diode (shown on page 3 of thread). I also noticed connected as shown, the diode would be forward biased (in other words passing current!!!) as soon as the Mom button is pushed...this is BAAD and not the way or intent of a snubber diode!...and this would cause an unlimited current to flow in the diode, and explain your PFFT result!

Options for Surferboy: You can actually continue to use the relay, now that this diode has gone to the happy hunting ground (is open!)...I expect the coil and working contact are still just fine....or you could (if qualified and know what your looking at when you open the relay, and are so motivated) open the relay and replace the diode, check, and reuse...but swap the terminals 85 and 86 connections, or it will happen again!

Suggested correction option for anyone else wanting to add this circuit: If you are using a relay without an internal snubber diode, go ahead and wire as shown...BUT, if you are using a relsy with integral snubbing diode, swap connections of term 85 and 86. This will reverse applied voltage so that cathode of the diode (which is on term 86 has Positive voltage applied, and therefore is out of the circuit and just along for the ride UNTIL the relay power is removed, at which time it will become fwd biased by the relay reverse spike, and will quench that as the design and God intended! Sorry for the long explanation, understandable by only elec qualified here, but I figured its best that way.

I actually wrote about this on my vintage Volvo site, if anyone is interested: https://www.sw-em.com/Ignition_Slave_Relay.htm#comparing_3_4_and_5_terminal_relays

I hope this helps, and Cheers from Connecticut!

[Abscate]

You could also just reverse the snubber diode to make that work correctly.
_________________
.ssS!

[Ronzo_volvo_guy]

Abcate;

Sure...there are often multiple solutions, but few are going to go into a relay to do that...when you can simply have the correctly polarized connections externally to assure function with no PFFFT effect!

Cheers

[Sodo]

Ronzo, what about using a simple relay like in the schematic (no diode)?
They are dime-a dozen.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[Ronzo_volvo_guy]

Sodo;

As I note in my explanation, that would be perfectly fine!...in fact, after the PFFFT effect, that is what his relay has turned into(!), a simple relay with no snubber!...and when there is no snubber in the curcuit, no polarity considerations are necessary.

BUT...using a relay with snubber diode is preferable if you ask me, especially in cars with FI ECUs with electronics...anything we can do to keep high voltage spikes (which occur whenever the coil current of ANY relay is interrupted) down and to a minimum, is not a bad thing! If you are cheap (frugal) and want to use the diode-less relays (I expect they are the least expensive) or you have an S-load of them already in stock from when you got a deal on a quantity, I understand...there is absolutely nothing wrong with adding a snubber diode EXTERNALLY across the coil (use a 1N4004, and again, observe polarity obviously because of that pesky PFFFT effect!).

Cheers

[Sodo]

OK thanks for the reply.
Thanks for clarifying the PFFFT.
Good to know when it's AOK (and not just during Covid times)

So you're saying that little coil sends out a voltage spike?
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.

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 )
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[Surferboy120]