Electronics I REALLY need a resetable fuse! please help me find one.

I need a fuse that can be reset like a house fuse. My idea is to implement this into a car's security system. Here's the idea:

The fuse control electricity going to the car's fuel pump. When the siren goes off, it trips the fuse and the fuel pump goes off. The only way to enable the fuel pump is to manually reset the fuse (which will be VERY well hidden)

I think that this fuse (or similar device if you know how to obtain the same effect) must be very sensitive because it has to be triped even if the alarm is only set off for a few seconds. If it could be wired to a switch or momentary switch, that would be ideal but is not a requirement.

I'm having a discussion about this on a car forum, so what better place to bring it then here? Please post any ideas!

 

The house fuse you are talking about is probably a circuit breaker.

You might be better implementing it with electronics and haveing a momentary reset swicth (smaller, easier to hide, less obvious etc)

What happens if it trips while you're going down the road

 

If it trips while moving, the car stalls. However, that's a chance I'm willing to take.

Does anybody know how to do this with electronics?

 

You could try a circuit breaker designed for car stereo's. The only problem would be finding one small enough for your use.

 

I'm under the impression that it's not very good for your car's engine to be running without fuel?

 

^ that's correct, but it's even worse for my car's engine to be stolen

 

You also might try looking into how the fuel pump shutoff works. I don't know what kind of car you have but all cars are supposed to have them, but depending on year and model it may/maynot be electronically controlled. (Fuel Pump Shuttof stops gas from leaving the fuel tank after a collision to help prevent fire/explosion, and can normally be reset by pressing a button)

 

Shutting off fuel to a fuel injected engine is usually a bad thing, as it requires re-priming the fuel system. The easier solution will be interrupting the ignition, the NO contacts of a relay can kill power, so that without it energised (alarm tripped) no juice to the plugs (engine won't start).

 

fords (old ones anyway) have a fuel trip switch under the spare tyre @ the back, trips if ur in a collision, im sure you could find info bout this and make one or just have a regular spst switch to ur fuel pump hidden under the dash and turn it off whenever u leave the car.

Col

 

Unless you were to empty the entire fuel system, drain the fuel lines, ect. it wouldn't require repriming the pump. It would just take a second longer for the engine to start. Either way, disabling the ignition sounds like a better idea, and most likely simpler. It might be helpful to let us know what year and kind of car you are dealing with also...

 

It's an 1999 Acura Integra GSR. I like the fuel pump idea better because the car will run for a couple seconds and shut off. That way the thief can think one of 2 things, (1) I take **** care of my car and it broke down, or (2) I have a fuel cutoff switch somewhere.

It is an undeniable fact that one of the most secure ways to prevent a thief from driving off with your car is to hide a fuel cutoff switch somewhere and disable the fuel pump whenever you leave.

For me that wouldn't work so well because I have a remote starter. I can't leave the car with the fuel pump off only to start it later. Besides a more convienient way to do this is to have an automatic fuel cutoff.


Let me put this in more basic terms. Lets say that there's 6 pins: pin A, B, C, D, E, F.
Pin C and D are normaly linked so that voltage can run between them.
Pin E and F are not linked so that voltage cannot run between them.
When Voltage is detected on Pin A, Pins C and D become unlinked and Pins E and F become linked.
When Voltage is detected on B, the device is basically reset: C and D are linked, E and F are not.
The more important thing here is that Pin A has to detect voltage for only a short amount of time to unlink C and D and link E and F. Even if the voltage flow on A stops, E and F will still be linked and C and D will not - the only thing that can reset this is voltage on pin B.

^ is there some kind of relay/coil for that? Can it be made using a few relays or something like that?

 

that layouit sounds very very similar to the lil alarm controller box on me bro's car, one of the relays died so it had to be hardwired. for ur remote start could you not do something with rf and a latch so that u could turn the fuel pump on and off remotly also, iirc maplin sell some keyfob sized rf transcievers.?

Col

 

that'd be too much of a hassle to carry something like that with me.

I know this car be done just the way I described it, I just need to find out how to do it.

 

It should be possible to build a circuit that will latch when the alarm is setoff and reactivate the fuel pump only when the car's central locking is unlocked (assuming you have it). That might be a better solution than a manually resettable fuse.

 

Great idea!
All I need now is for someone who know about circuits to help me out (cause I sure as hell ain't going to be able to figure it out!)

 

Ok, the first thing we need to figure out is how to detect if your alarm is set off.

The second thing we need to figure out is how to detect when your central locking is deactivated.

Assuming they're both linked to your car's computer (and i don't know much about car electronics, but it seems to make sense) it should be ok to put some kind of TTL converter on a specific wire from each system. You'd have to know the specifics about the systems in your car though. Shouldn't be too hard to find.

I'm sure I or someone else could make a circuit diagram no problem if you can give us some information about how your systems are wired up

 

my alarm is an aftermarket one and I know where all the wires are so it's not a problem.

When the alarm is set of, 12V is sent to the siren. A wire can be attached to that and that will be the trigger.

When alarm is disarmed, it unlocks the doors. A wire can be attached to the unlock wire. A diode will be put after the 2 wires come together so if the doors are unlocked from the inside, no voltage will go through the wire that will lead to the "reactivate fuel pump trigger"

 

So what you actually want to happen is that the fuel pump stays deactivated until the alarm is switched off? Thats the simplest way of doing it; just sensing when there is voltage on the wire going to the siren and turning off the fuel pump.

If this is the case, you could simply use a not gate to flip the input from the siren, so when it is switched off, the output is high and the fuel pump is turned on, otherwise it is turned off.

It would actually make more sense, however, to use a normally-closed relay, so the relay would only put strain on the battery from the coil when the fuel pump is switched _off_. It would just be a simple case of:

a normally closed relay, with a protection diode on the coil, wired across the alarm +12v and ground, connected in series with the fuel pump. However, it would have to be a fairly heavy duty relay (how much current does your pump draw, and consider that the relay will have to carry this current all the time in normal operation)?

This way, the fuel pump would switch off when the alarm was on.

You might be better off asking someone else for help with a self-latching circuit, as I'm too tired

 

Is important that the fuel pump be ON while the alarm is armed.

Let me put it this way, the fuel pump should ALWAYS be on, I need it for my remote start. The only acception is if the siren for my alarm is activated, then the fuel pump is cut off.

Another REALLY important thing is in the event that the siren is activated (the fuel pump will be disabled) and then the siren is disactivated, the fuel pump must still STAY off!!! I cannot stress enough how important this is.

The only way that the fuel pump should be re-enabled is if the alarm system is disarmed by the remote (don't worry about what wire that is on the alarm, I know where it is)

 

You might look at a circuit using a PIC microcontroller with an inbuilt battery (a number of D-cells possibly), that way even if your main battery is disconnected the fuel pump will _stay_ off until you reset it. I'll try and get a schematic, parts list and program ready for you tommorow

By the way, don't you think you might be worthwile turning off your starter soloind(sp) as well, so the engine can't crank over? Even if they couldn't steal your car, they could cause a fair bit of damage to the engine cranking it over with no fuel pump running for a few minutes.