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12v breaker. How? 

 

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Posted: Thu Sep 20, 2007 2:56 am 
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66 coupe wrote:
if a fire starts, killing the power really wont do much. The fire needs fuel, and turning the key off will stop that.


I am not talking about in the engine bay, I am talking about the whole car. For example, I want the isolator switch in the boot and I want the switch to kill power to absolutely everything. So say a short happens in my wiring in the boot and sparks which starts a fire, I could stop the spark with the switch.

 

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Posted: Thu Sep 20, 2007 9:42 am 
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When the engine is stopped the only source of electricity is the battery. When the engine is running, the alternator also creates electricity, usually enough to keep engine running and recharge the battery. A normal wire would probably burn out and discontinue the circuit before you could pop the boot and flick the switch. Unless you wanted to put a switch on every wire in the car to isolate power individually to everything, turning off the key will iso most things including ignition spark, fuel. Battery iso switch will do everything once ignition is switched off, which in turn stops alternator creating the other power source. An extra switch on ignition wire could be put in boot as well but....
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Posted: Sun Sep 23, 2007 4:25 pm 
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Use a contactor. A contactor is effectively a big relay which can handle lots more current and has silver contacts to stop them burning out when they arc. They usually have 3 inputs so you can divide your wiring up into 3 and spread it across. Get 1 with 3 normally closed contacts so it doesn't need to be energised to let the power pass through it. Make sure it has a 12v DC coil. go from your battery +ve to a switch, from the switch to the contactor coil and from there to -ve terminal.

So if you turn the switch on, the contactor coil energises and disconnects all subsequent circuits hooked up to it.

edit: can one of the mods please fix gyzmos URL so the thread isn't f**k up. :)

 

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Posted: Sun Sep 23, 2007 9:08 pm 
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smiley235 wrote:
Use a contactor. A contactor is effectively a big relay which can handle lots more current and has silver contacts to stop them burning out when they arc. They usually have 3 inputs so you can divide your wiring up into 3 and spread it across. Get 1 with 3 normally closed contacts so it doesn't need to be energised to let the power pass through it. Make sure it has a 12v DC coil. go from your battery +ve to a switch, from the switch to the contactor coil and from there to -ve terminal.

So if you turn the switch on, the contactor coil energises and disconnects all subsequent circuits hooked up to it.


They are made to extinguish an AC arc, won't work well for high current DC. As long as you aren't using massive current when you switch it off, it should work though.
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Posted: Sun Sep 23, 2007 9:15 pm 
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hmm, true. We always use them at work but only for AC, not sure bout DC in this case.

 

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Posted: Sun Sep 23, 2007 9:16 pm 
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Hopefully it wouldn't be used that often for the tips to melt that significantly.

The problem with using a normally closed setup is you're using power to disconnect power - if the fault has caused a malfunction in your circuit, you may not be able to activate the contactor.

Another aproach would be to use the normally open tips, but your ECU is going to need its KAM power regardless, so think your circuit through.

 

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Posted: Mon Sep 24, 2007 1:31 am 
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A relay inline with the main fusible link.
This will cut the power to everything bar the starter motor (and depending on model, the ABS module)

Won't however cut the power line to the battery in the boot.
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Posted: Mon Sep 24, 2007 10:44 pm 
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Jaycar sell a 120A circuit breaker (designed for car audio use), but it's got a switch on it too, so as long as your expected load isn't more than 120A it'll work fine for any purpose.

 

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Posted: Wed Sep 26, 2007 1:13 pm 
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Lots of useful information here, thanks guys!

 

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