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Old 15th Dec 2020, 4:22 pm   #1
GMB
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Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,086
Default Advice on mains current sensing, safely

I need to build a passive thing that works out that our new TV is on to power up the HiFi for the sound (the TV, being modern, has crap sound).

The obvious solution is to sense the mains current being drawn by it since, being modern, it's power consumption is several times that of a valve-based TV (unbelievable - about 400W - don't need the central heating these evenings).

My thought was a current transformer but I am aware that these are possibly dangerous in the situation of a short circuit. So just before the fuse blows the current transformer maybe becomes a ball of plasma? This idea is based on it stepping up somewhat so that there is little voltage drop of the mains - not that it will be much of an issue as the mains here is always on the generous side of the right answer.

It will have to extract enough energy to power a relay.
Has anyone actual expereince of doing this or ideas to make it safe?
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