Can anybody help me with the design of this type of switching. I have limited experience with electronics but I am capable of putting this together if helped. I wish to switch on a machine 120V , 12 amps, using a low voltage circuit [12v ish] The frequency of this operation would be about 100 times a year. I would like to do this as safely as is possible.

Is it advisable to power the low voltage circuit from a transformer off the 120V supply or would a battery be the better way to go?

How do the 2 circuits interface?

Any help would be greatfully received.

Thank you.

 

You can use a relay or a solid-state relay (triac + optotriac). You can use either battery or transformer for power; for a basic circuit, the battery will need replacing when it gets flat, while the transformer will draw power all the time.

You may of course switch the transformer on at the same time as you switch on the machine and recharge the battery - this way there is no idle power consumption, and the battery never becomes flat.

 

The cleanest way to go is one of these: This one is a bit expensive and some overkill, but I have seen these sell for much less from time to time.

Look for one rated at 25A at DigiKey or Mouser. DC in, AC load, totally isolated.

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Mike ML.

 

Here is another clean way and probably cheaper.

The SSR is designed for a maximum current of 16A at 115VAC. There is plenty of space on the PCB for a heatsink if necessary.

SSR type is Sharp S116S02, fully plastic encapsulated.

Boncuk

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Proper Planning Prevents Piss Poor Performance

 

Thank you for your help with this. I am going to build a central vacuum unit using a standard workshop vac and a cyclonic attachment + HEPA filter. I will let yo know how things work out.