Switching 220V ac

Thread Starter

Konstabel

Joined Jan 31, 2008
52
If I would like to switch a kettle element on and of using small signal electronics, would it be better to do the actual switching using a relay or a circuit using an optocoupler?
 

beenthere

Joined Apr 20, 2004
15,819
Optocouplers can't handle that kind of voltage or current. They can provide turn on/off signal levels to solid state relays (SSR's), though.
 

Thread Starter

Konstabel

Joined Jan 31, 2008
52
Hi!

My question yesterday was not completely put.

I meant to ask: If I would like to switch a 220Vac load, what would be better? A solid state relay or a optocoupler/triac combination?
 

studiot

Joined Nov 9, 2007
4,998
If you want to switch on and leave on use a relay, solid state or mechanical.
If you want power control, switching on and off every cycle (or part cycle) use a triac.
The optocoupler can also be used with a relay.
 

h.d

Joined Oct 22, 2007
150
triac is faster than relay in switching
and have lonfer life time
when you use relay you need optocoupler becuase its through the current in the two sides.
 

studiot

Joined Nov 9, 2007
4,998
triac is faster than relay in switching
and have lonfer life time
when you use relay you need optocoupler becuase its through the current in the two sides.
Triacs are not faster than solid state relays (some modules use a triac!)

Proper mains relays are fully isolated between activator and contacts and need no opto isolator, though one can be used.

Any form of solid state switching is vulnerable to its environment, which is why the manufacturers of my boiler for instance use relays in the control electronics in the cabinet. It just gets too hot in there.

But this is away from the point. If you use a triac you have to employ circuitry to switch it on every cycle. This generates RFI problems that need dealing with. So if you just want to use a small low voltage, safe current to switch on/off a large one every now and then and/or have a hostile environment use a mechanical relay. If you want to switch on and off at higher frequency use a solid state device. If you want to switch on and off for power comntrol reasons use a triac plus all the attendant RFI suppression circuitry.
 
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