Blowing fuses in a cars fuse box electronically

[Wond3rboy]

Hi, this is an idea that a friend of mine floated.He wants to make an antitheft system by blowing up the fuse(s) in the car's fusebox. Since he is a student of mechanical engineering, he wanted to give my ideas on how one can manage the burning part. What i was thinking that one could use a boost regulator and than increase the voltage(current) to burn the fuse?. The overall idea is to use a GSM module, GPS and an arduino(to make his electronic part simpler) and make an antitheft system.

He does not want to put an other battery to provide the burining current.

 

[Diver300]

You can just connect a thyristor between the output of the fuse and ground. The fuse will blow as soon as there is power from the battery. Look up "crowbar circuit"

You don't need to increase the voltage to blow a fuse. If you increased the voltage you might damage what is connected to the fuse. To blow a fuse, you need several times its rated current. You should that increased current by reducing the resistance of the load, not by increasing the voltage. If you increase the voltage and keep the load the same, you would need maybe 100 volts or more, and you would probably cause the load to fail before the fuse failed. Also, some loads might be disconnected at some times so it wouldn't matter how much you increased the voltage, the fuse would never blow.

You might want to use a buck regulator that would reduce the voltage, and at the same time increase the current, so that the fuse would blow while taking less than the fuse rating from the supply. However, there is little point. The car battery will supply around 500 amps to turn the starter motor, so a spike of 100 amps to blow a 30 amp fuse isn't a problem.

 

[Wond3rboy]

Thanks driver. I will advise him on the thyristor.

 

[Wond3rboy]

Hi,

So i got him to work on the thryristor. The fuse rating being 80A so he will need to put more than 80Amps through the fuse box(i have still doubts about the battery's ability to supply that much current and have asked him to check out its specs). Till then, he has asked me to give a him a component number. So searching on google, i got some components numbers and wanted you peoples' comfirmation on this

**broken link removed** more specifically


**broken link removed** (its cheap)

Its surge current is 100A but average current is 12A, i know that normally its only going to allow 12A to go through but the 100A thing is only going to happen for an istant(basically the time it takes for the fuse box to blow).

The SCR(module) that is rated at 100A is this one

**broken link removed**

But this ones really expensive 146$. Any suggestions?

 

[tcmtech]

A standard 12 volt heavy duty relay would be more than enough to take out any vehicle fuse and survive.

A simpler circuit is to just disconnect the power for the fuel pump, fuel injectors, or starter circuit between the key and the starter solenoid of which all three typicaly get their power from dedicated power relays some place in the main electrical systems in most vehicles opposed to blowing fuses.

You cant start a vehicle that doesn't have any fuel, spark, or working starter!

As for automotive battery peak amp capacities I suggest you read up on what CCA stands for regarding vehicle batteries.

 

[Diver300]

A car battery can supply way more than 80 A. Some cars have fuses up to 250 A and there isn't much point in putting a fuse that could never blow.

In fact, connections to starter motors can't have fuses, because the short-circuit current isn't much more than the running current. If they need circuit protection, that is done with an small detonator that blows the connection.

Can't you find a smaller fuse to blow? There must be many smaller fuses that would stop the car. If you have to blow an 80 A fuse, then 100A is nowhere near enough. If you look at https://www.tlc-direct.co.uk/Figures/3.13b.gif you will see that you need somewhere near 500 A to blow and 80 A fuse in 1 second, and the 12A thyristor is only rated to 100A for 1/120 seconds.

Also, you don't know how big the current is going to be, so you need to allow for higher currents or longer times. To take out an 80A fuse you need a seriously large thyristor.

 

[Sceadwian]

Blowing fuses seems like an overly complicated way of disabling a car, you could simply put a small solid state relay on the ignition line in an out of the way place, you could remove power to the computer, or some other critical component to starting the car which make far more sense than the complexities intentionally burning out a safety component without hindering it's function.

 

[tcmtech]

Blowing fuses seems like an overly complicated way of disabling a car, you could simply put a small solid state relay on the ignition line in an out of the way place, you could remove power to the computer, or some other critical component to starting the car which make far more sense than the complexities intentionally burning out a safety component without hindering it's function.

Exactly. Given the complex electronic control systems present in vehicles there are numerous ways to completely immobilize one with nothing more than one or two hidden $1 micro toggle switches that interrupt the power to a relay that activates a critical component or system.

Cheap, simple, resettable, 100% effective, and not destructive to anything.

 

[nsaspook]

In fact, connections to starter motors can't have fuses, because the short-circuit current isn't much more than the running current. If they need circuit protection, that is done with an small detonator that blows the connection.

I think its normally called a "electrical fusible link " not a detonator.
https://www.awcwire.com/ProductSpec.aspx?id=fusible-link-wire

 

[audioguru]

A car battery can supply way more than 80 A. Some cars have fuses up to 250 A and there isn't much point in putting a fuse that could never blow.

Haven't you seen photos of some of the "cars" in Pakistan? They are tiny with only 3 wheels and a tiny little battery. They might not have a starter motor.

 

[Wond3rboy]

Hi, thanks for the replies guys. Really a trove of info that i can pass to him, the relay thing would be a lot more effective(doable, since these would be most probably available). Like AG said, most of the cars here are cheaper versions(but we do have expensive cars too(hummers, mercedes, bmws etc), the people who can afford the $$$, what AG is talking about are called rickshaws which are basically small taxis..not for which this system is intended for) to make them marketable. Also, here since there is not much expertise a surgical disconnection is not very possible but i will ask him to explore that as well. Will update you on the progress. Thanks again.