Help with current sensing relay for projector screen

[atomic_chris]

Hi,

I have a 12v relay circuit used to drive my electric projector screen, normally driven from an output on the projector, but I've just changed my projector and it has no output now.

I'm probably being naive, but I wandered if I could just get a toriod, say

**broken link removed**

couple it to a transistor to switch the normal 12v supply for my relay circuit to the high input of the relay, thus opening the relay whilst the projector is consuming current.

It's UK mains 240v and the projector consumes about 1amp in use.

If it works in theory, what type of transistor/coil would be suitable, or does anyone have a better way to accomplish my goal?

Cheers,

Chris.

 

[blueroomelectronics]

What sort of communications does it have? RS232?

 

[crutschow]

You certainly could rectify and filter the AC output of a current transformer to turn on a transistor. A 1:100 turns ratio (input to output) would give you 10mA of current for 1A of power line current. The 1-turn transformer primary input would be in series with one of the two power wires going to the projector. Use a bridge rectifier and filter to generate the DC current to drive the base of the transistor.

Your could also use an AC current relay such as found at **broken link removed**. One of the over current AC type relays should work. I'm sure other companies also make such relays.

 

[Rossgooding]

your machine might have had a shortcircuit