AC Mains switching with relay - design considerations?

So, I'm thinking of doing a "AC MAINS" relay for the "ON SWITCH."

Back in my day of working on TV's and Stereos, the way most of them "switched the AC MAINS ON." was-

They would have a little "Stand By" transformer permanently attached and running off the AC LINE IN, putting 12v on the main AC relay, IR sensor etc, logic stuff etc... All waiting for the "ON" command from either that TACT switch or IR "low"

I have a neat little EAO lit push switch that I like to use... thought about using it for power, but would obviously have to do the relay circuit.

Anyone designed with AC ON relays like this? Any design considerations to mention?

jwhmca said:

So, I'm thinking of doing a "AC MAINS" relay for the "ON SWITCH."

Back in my day of working on TV's and Stereos, the way most of them "switched the AC MAINS ON." was-

They would have a little "Stand By" transformer permanently attached and running off the AC LINE IN, putting 12v on the main AC relay, IR sensor etc, logic stuff etc... All waiting for the "ON" command from either that TACT switch or IR "low"

I have a neat little EAO lit push switch that I like to use... thought about using it for power, but would obviously have to do the relay circuit.

Anyone designed with AC ON relays like this? Any design considerations to mention?

Click to expand...

You could save on another transformer if you can get a relay with a mains voltage coil, and your switch can handle the voltage. Greener that way, off is off,  no standby current from a transformer that is on all the time.

A triac is another idea, at least one well known power amp manufacturer went to this when they got tired of warrantying burned rocker switches switching a 1KVA power transformer.

Gene

I use old X-10  power line remote controls. With appliance relay modules.

I recently did a prototype safety (?) device, based on a GFCI outlet with a 3 pole relay in front of it. The relay had a 120VAC winding, so I powered it from the output side of the GFCI, so if the GFCI outlet tripped and turned off, the relay opened up the safety ground too.

I jump started the rig with a triac to provide power to the GFCI input until the relay latched on. I also measured fault current flowing in the safety ground leg, so I could open and disconnect the relay if I sensed enough current to harm humans (>10mA). The GFCI trips and opens if 5 mA leaks from it, but I could also trip from external fault currents in the safety (like from a different power distro).

I got one prototype working on my bench but it was expensive and likely to cause a wrestling match with UL to ever approve opening up a safety ground (the foundation of all their safety engineering).  I have known safety grounds to kill people when miswired, like sometimes happens in live sound reinforcement. 

JR

PS: For some extra margin of safety, my smart outlet couldn't even power up if plugged into a miswired outlet. I may have a slightly used relay to sell you, but it's a big honker to handle 15A or so.  You probably want a smaller cheaper relay.

TV series relays were the most common IIRC...

Microwave ovens use relays to switch 10A-20A magnetron supply.

It is a good design if the current involved means an expensive switch.  Or any digital remote device.  Or controlled sequencing.
I think of the widdle toggle switch on the SSL 4K power supplies.
Mike