On Sun, Aug 31, 2003 at 08:19:22PM -0800, Joe enlightened us thusly
> At 12:34 PM 8/30/03 -0800, you wrote:
> > I have not seen them for years. a little line current
> > all
> >the time, so this thing would have to distinguish between a fraction
> >of an amp, and the higher draw when the TV is actually on.
>
> Use a step down transformer in reverse. Put the low voltage side
> (secondary) in series with your load and connect a relay to the high
> voltage side (primary). Use a transformer that has a LOW voltage
> output, say 3 volts, and a current rating similar to that of the
> load that you're monitoring. That should give roughly 3 volts line
> drop to the load being monitored, that shouldn't affect the load.
> The relay needs to roughly match the output (primary side). You'll
> have to play with the ratings and you may need to put a dropping
> resistor in series with the relay to decrease it's sensitivity. The
> transformer should have low voltage output when little current is
> flowing to the load (the load is off). When the load is on and
> drawing appreciable current then the output voltage will rise and
> engage the relay.
Just lurking on this thread, I'll throw one more approach. Televisions
use ~200W on, but may exceed one amp in inrush currents.
Drop a few volts - A few diodes in series or cathode to cathode 3V3
zeners (5W). Across this put 2 optocouplers in antiparallel with a 10
ohm resistor in series. A Small bleed resistor will make sure the
optocouplers aren't triggered by the bleed current.
That's 6 components (2 zeners, 2 optocouplers, 10 Ohms and some bleed
resistor). The trouble with asking is that you have to think all these
different ideas through ;-).
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
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