This circuit enables you to connect both your washing machine and your tumble dryer on one wall outlet,
without blowing the fuse!
The trick is that the washing machine only consumes full power when heating the water.
During the other stages (pumping, tumbling, centrifuging) the power consumption is much lower.
The circuit switches off the tumble dryer during the (brief) time that the washing machine is heating the water.
I designed & built this circuit years before I started my web site, it has been in use ever since, but I forgot about it!
Certainly a reliable design….
Because it has proved its reliability, I just copied the old circuit diagram without any changes.
The current of the washing machine if fed through 25 milliohm shunt resistor R6.
R6 is built with 40 x 0.25W standard resistors of 1 ohm.
Note that the dissipation in R6 is quite high at 16 Ampere: 16×16x25milliohm=6.4 Watt or 160 mW per resistor.
For 120 V application, the maximum current will be even higher; you will need even more resistors in parallel for R6!
R1 & R2 create a reference voltage of half the supply voltage.
When the AC signal across R6 is high enough, it will trigger the schmitt trigger built with IC1, R7 & R8.
The sensitivity can be adjusted with R5, I used 4 100W lightbulbs as load to set my circuit on about 400 Watts.
When IC1 is triggered, a 50 Hz square wave will appear on output pin 6. C5 will be charged fast through R9 and D1.
When C5 is charged, the schmitt trigger built with IC2 is triggered and its output (pin 6 ) will become high.
When the output of IC2 is high, the relay will switch off the tumble dryer.
D1 protects T1 against high voltage peaks from the coil of relay Re1 when it is switched off.
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