mosfet help?

[floorboy]

Hi, new guy here....

I am thinking about making an alarm of sorts for my boat.

Is there a way to wire a mosfet so that when a ground is broken it powers up the alarm????

I have one made now out of a relay and it works but I was told that the power draw on the relay would kill the batteries in short order. (2 days?)

Also...If I was to make multiple triggers on this can I wire in some diodes and tie into the single ground, or would I need multiple transistors???

Sorry I know about regular wiring stuff but I am transistor challenged.

Also where can I get something like that???

 

[Hero999]

It's pretty easy.

This circuit is fine for 12V, for a 24V you'll need to add another resistor.

 

[indulis]

Just remember that the MOSFET will have to have it's own ground back to the battery and the gate resistor should be connected to the ground you want to monitor. Also, watch out for common mode current in the monitored ground because if it's high, the voltage drop across it could start to turn the MOSFET on.

 

[Hero999]

watch out for common mode current in the monitored ground because if it's high, the voltage drop across it could start to turn the MOSFET on.

Just don't connect the sense wire to another unknown ground, connect it directly to the source.

 

[floorboy]

THANK YOU!!! Ok where do I find something like that?? What about multiple triggers?

 

[Hero999]

What do you mean by multiple triggers?

Do you want it to trigger when any wire is broken?

Try figuring it out for yourself, post the answer here are we'll tell you if you're right.