What would happen if he was to push the button and then not start the vehicle for whatever reason?

That's an odd situation, but the relay stays latched only as long as the ignition switch is on.
Turning off the ignition switch will kill the latch, and require another button push when the ignition is turned back on.
It has nothing to do with whether the engine has been started or not.

 

That's an odd situation, but the relay stays latched only as long as the ignition switch is on.
Turning off the ignition switch will kill the latch, and requires another button push when the ignition is turned back on.
It has nothing to do with whether the engine has been started or not.

I see what you’re saying. In theory that would work too, might be worth looking into.

 

Of course that latched relay is also unlikely to drop out due to the voltage drop from starting.

 

If you read posts#1 and 13 you'll know..

So where's the coil current rating?

Tell us what the relay part number is. Someone will find a data sheet and give you some pretty good characteristics on it.

That's not a data sheet, that's a functional connection sheet and contact ratings. Nothing about the coil.

The TS wanted a cap and resistor to trip a relay after some period of time. Without knowing what the current draw is - it's anybody's guess.

 

Just make a removable gas pedal. Where's a thief going to go at an idle?

Now THAT's outside the box for sure.

I have to agree with others. Why are you trying to trick a thief with a timer that will self reset after some period of time?

 

I see what you’re saying. In theory that would work too, might be worth looking into.

This is what I would do. Essentially after one button push you have a regular car until the ignition is turned off.

 

Now THAT's outside the box for sure.

I have to agree with others. Why are you trying to trick a thief with a timer that will self reset after some period of time?

It won’t self reset? Needs some one to activate it

 

Another anti-start trick that worked very well when a friend added it to his car was rather novel cheap, and uncommon so that nobody would suspect it or look for it. We wired the cigarette lighter across the breaker points. That was enough to keep the spark plugs from firing. So when he parked he would just hit the lighter, which was not at all obvious. And we replaced the lighter fuse with a burned out fuse so that if anybody was checking they would see that was why the lighter did not pop out. That was a 1966 car, so the TS car may also have a breaker points ignition system. It was simple to hide that extra wire in the engine wiring harness, and in the dashboard wiring as well.
Of course it would also help to add a decoy switch that was poorly hidden, and when the potential thief flipped that switch it would sound the horn rather than allowing the car to start. Make life a bit harder for the bad actor. That circuit could even have a latching relay with a hidden reset button. Orsimpler, use a center off switch with both directions sounding the horns.

 

We wired the cigarette lighter across the breaker points.

Marvelous. Wish I'd have thought of that back in the 70's.

 

Back in the 60s and 70s I would fit a hidden switch that would switch either a several microfarad capacitor or a zener diode in parallel with the points. This was based on if a thief was trying to find our why it would not start they uould still see the voltage across the points changing from zero to 12 volts when they they turned the engine slowly. (With a spanner on the nut on the end of the crankshaft or pushing it with it in gear.)
I think now just disabling just the ignition may damage the catalytic converter with unburned fuel.

Les.

 

If the engine will not start there is not a problem. When the engine first starts the hot exhaust will evaporate the fuel before the converter gets hot enough to ignite it.

 

Modern vehicles have electric fuel pumps. Disabling the fuel means two things: Not starting AND not flooding the engine with unburnt fuel. Older vehicles with mechanical fuel pumps, you can change them to electric fuel pumps. Then a hidden switch would do its job. With carburetors holding a reservoir of fuel, the engine may start but soon stall out when the gas in the bowl has depleted - meaning a thief wouldn't get very far before sitting in an obviously precarious spot, conspicuous and prone to attracting attention.

If the engine is fuel injected, cutting the fuel supply means a non-starting engine.

 

OK, this is not by amy means a "modern vehicle", since the TS claims it has no starter relay. Back in the six volt era there were cars that had some sort of mechanical switch that the driver stepped on to crank over the starter motor. That was prior to having the solenoid kick in the starter pinion gear. My grandfather had a car like that when I was very young. And it was an old carat the time. The vehicle in discussion is much newer in that it has a 12 volt system. It might have "A Bendix" device to engage the starter instead of a solenoid. But those vehicles did have a starter relay rather than have a contact on the solenoid that engaged the pinion.

And the original concept appears to have been to have that 30 second time after pressing the hidden button to crank the engine. An interesting concept but it is not that clear how effective it would be.
Of course, if that is what a customer wants, then provide it. The customer IS NOT Always Right, BUT they ARE the one with the money.

 

OK, this is not by amy means a "modern vehicle", since the TS claims it has no starter relay. Back in the six volt era there were cars that had some sort of mechanical switch that the driver stepped on to crank over the starter motor. That was prior to having the solenoid kick in the starter pinion gear. My grandfather had a car like that when I was very young. And it was an old carat the time. The vehicle in discussion is much newer in that it has a 12 volt system. It might have "A Bendix" device to engage the starter instead of a solenoid. But those vehicles did have a starter relay rather than have a contact on the solenoid that engaged the pinion.

And the original concept appears to have been to have that 30 second time after pressing the hidden button to crank the engine. An interesting concept but it is not that clear how effective it would be.
Of course, if that is what a customer wants, then provide it. The customer IS NOT Always Right, BUT they ARE the one with the money.

This car is a 1967 Chev. The two main ways one would inhibit start is to interrupt either the start signal or the power supplyto the coil. I have essentially done the same but with a momentary switch.
The setup is not intended to be able to kill a running engine, but more so inhibit start to a person not familiar with the setup.

With modern cars, there’s a lot more options. Fuel pump, ignition supply to ecm, start signal, park neutral switch, and many more. Obviously not all of those options will kill a running engine.

 

It won’t self reset? Needs some one to activate it

Sounds like it can be draining the battery.

I think temporarily applying starting power OR preventing it seems like the wrong way to go. But this is your thread and you can take it anywhere you like. Who above said electronic fuel pumps?

Modern vehicles have electric fuel pumps. Disabling the fuel means two things: Not starting AND not flooding the engine with unburnt fuel.

Thought so.

 

Sounds like it can be draining the battery.

I think temporarily applying starting power OR preventing it seems like the wrong way to go. But this is your thread and you can take it anywhere you like. Who above said electronic fuel pumps?

Thought so.

How would you do it?

 

I would install a ~$59.oo Car-Alarm,
which comes with all the "Bells & Whistles", and 2-Remote Key-Fobs.
.
.
.

 

Back at post #1, the TS was asking about how to keep the timer from dropping out. That sort of timer scheme does not need to draw any current at all until it is triggered. Of course, some of the suggestions would need a mains powered supply to be functional.
Really, a relay latching circuit with a timed drop-out will do the job quite well. The whole purpose was to prevent cranking the engine if the timer had not been set, the time out was to make it reset without the user needing to remember to do it.
My guess is that the timer used was sensitive to the momentary voltage drop when the starter motor is first connected. That drop is very short and most meters will never see it.
One work-around would be to use a regular relay latching circuit powered from the "ignition" contact on the switch, so the hidden button would need to be pushed after the key was turned to "run" but before it was turned to "start". Then the function would reset whenever the engine was switched off. The only downside is that the relay would stay latched as long as the engine was running.

 

The only downside is that the relay would stay latched as long as the engine was running.

How is the small power required by the relay in a running vehicle a downside?

 

Who above said electronic fuel pumps?

Yes, that was me.

How would you do it?

The 67 Chevy likely has a mechanical fuel pump on the left side of the engine, below the exhaust manifold. If you want to go with an electric fuel pump you'd remove the mechanical fuel pump and put a cover over the opening. They sell such covers with gaskets to seal the engine. Then there would be a bit of plumbing taking the fuel from the original delivery tube that comes from the tank to the pump. The pump, when powered, pumps fuel into the carburetor where the float valve allows fuel in at low pressure and reserves that fuel in the bowl for the carburetor when you step on the pedal. With an electric fuel pump you can disable it by interrupting either the power or the ground. But so could a sharp minded thief who knows you have an electric fuel pump. Of course, the thief is in a hurry. If he can't get it started right away he'll abandon the endeavor in search of a quicker steal.

Modern fuel pumps are designed for higher fuel pressure and would not be suitable for carbureted engines. You'd have to search for the right kind of electric pump, but I'm sure you can find one.

If I were a thief and knew you had an electric pump I'd have a jumper wire ready to connect the positive lead to the pump to turn it on. Therefore I could easily start the car. But if the ground line is switched (if the body is not grounded) then it might take a minute more to figure that out. Using a DPST switch you could interrupt both power AND ground. The thief would have to know enough to both supply power and supply ground. But the more time he has to think about how to defeat your home brew security system the more time he has to think about moving on.

As for the starter on that car, there's probably a small yellow wire that goes to the starter solenoid mounted on the side of the starter. Interrupting that line will prevent the car from being started with a key or a picked key lock. But it won't prevent someone from touching the solenoid input screw to the battery cable that is conveniently right there. Easy to crank the starter with just a screwdriver. I've done that. But without the key the ignition is turned off. Hence, a hot wire connects power directly from the battery to the coil. That's where the term "Hot Wiring" comes from. Problem with that is that 12 volts directly into the coil can overheat it and cause failure. There's either a ballast resistor in line with the coil feed or in some slightly newer cars, there's a resistance wire of a pre-determined length to provide sufficient current to run the coil.

Modern cars won't run unless the computer is active. I've never had the need to jump or hot wire one of those. It's probably easier to rip the key assembly out of the steering column and stick a screw driver into the cavity and turn the key that way. That unlocks the steering wheel and allows the car to be started.

My neighbor had a car that wouldn't start. It could be hot wired and it would run but as soon as you removed the hot wire it would stall out. His key has a chip (a resistor of approximately 35KΩ if memory serves. The very fine wires that ran up the steering column to the key developed an intermittent connection and eventually completely failed. To fix that issue we installed a resistor under the dash of the correct value and he could then start the car without any problems. It was a defeated security system. Even if you pulled the key lock out of the column you still couldn't start the car without the right key.

How I would go about protecting a 67 vehicle would probably be to interrupt the ignition power. That's easy enough to defeat but you have to know what's going on to do that. There again time comes into the equation. The thief doesn't want to spend time figuring out how you protected your car. So some thieves have tow trucks that can quickly grab a vehicle and tow it to a chop shop. A hidden tracker with its own battery can solve the problem of them discovering the tracker and disconnecting it. For every invention there's a counter invention. For every solution there's an UNDO solution.

The alarm I never built was one that sensed motion and triggered a pre recorded screaming of a woman screaming bloody murder. LOUD AND CONTINUOUS would certainly make a thief abandon all hopes of taking your vehicle regardless of by breaking your security or if they tried to tow it away. Maybe one day I'll get that far and make such a device.