Solid State Relay to Switch Transformer?

[m_c]

I'm with you there Robin! Way too noisy :yes:

I dunno. I find it reassuring hearing a relay clicking, although I do cringe when my phase converter start-up relay chatters when a big load gets switched on.

If you want to make your own, Google for the MOC3040

I'll keep that info handy for future use, but at the moment, I'll stick to buying something that should work how it's supposed to!

[irving2008]

If you want to make your own, Google for the MOC3040

An opto-isolated triac with zero crossover switching.

Add one resistor to limit the gate current and use it to drive the fat triac of your choice.

Not all SSR's feature zero cross over, but that's what data sheets are for :D

I was of the understanding that SSR weren't TRIACS but series hi-power MOSFETS. A TRIAC wont turn on a zero crossing only off, and you usually use a diac to trigger them when the voltage reaches the trigger point, about 25v or so - thats why they work in a dimmer/speed control circuit by delaying the turn on point with an RC network. An SSR is on all the time it is enabled whatever the applied volts although there is a voltage drop across them of about 0.6v and they have an Rds(on) resistance which sounds more like a MOSFET with a series diode (the reverse diode in the second MOSFET).

[Robin Hewitt]

I used to avoid triacs because of the need to retrigger them constantly to keep the power flowing but the opto-isolated triac makes that so easy. LED on = power flows.

That's why they made the MOC3040, a zero crossing variation of the good old MOC3020. It has no meaning other than as a switch.

I got the MOC3020 + power triac + 1 resistor circuit from an old RS catalogue which detailed an SSR they were touting. Okay they might have moved on since then but you can still build an opto isolated 25A mains switch for around a quid.

I used the circuit to switch on a half horse cap start motor which leapt convincingly until I bolted it down.

[irving2008]

I used to avoid triacs because of the need to retrigger them constantly to keep the power flowing but the opto-isolated triac makes that so easy. LED on = power flows.

That's why they made the MOC3040, a zero crossing variation of the good old MOC3020. It has no meaning other than as a switch.

I got the MOC3020 + power triac + 1 resistor circuit from an old RS catalogue which detailed an SSR they were touting. Okay they might have moved on since then but you can still build an opto isolated 25A mains switch for around a quid.

I used the circuit to switch on a half horse cap start motor which leapt convincingly until I bolted it down.

Just had a look at the data sheet for a MOC3040... its turn-on volts is 20v so not truely zero-crossing but as near as makes no difference. But at 43p, coupled with a 97p 60A continuous-rated 600V triac and a 330R resistor its a good way to switch spindle motor or similar...