Best way to drive a 240V coil relay?

chris-s

New Member
Whats the best way to drive a relay that has a 240V coil from a pic? I was thinking of triac and triac driver, but somehow that seems overkill. Would I need a diode across the coil?

Cheers!

Chris
 

Michael 2727

Senior Member
The cheapest way would be to use a 5V, 6V or 12V Relay to switch the 240V.
( you will need a transistor & diode etc )
Most relays have a Low voltage equiv, can you just swap it ?
If the relay is a Motor Start type, they can have a 12V-AC or 24V-AC
and sometimes DC equiv replacement.

Whats your App ?
 

chris-s

New Member
The cheapest way would be to use a 5V, 6V or 12V Relay to switch the 240V.
( you will need a transistor )
Most relays have a Low voltage equiv, can you just swap it ?
If the relay is a Motor Start type, they can have a 12V-AC or 24V-AC
and sometimes DC equiv replacement.

Whats your App ?
Thanks for the reply, "Most relays have a Low voltage equiv, can you just swap it ?", now why didn't I think of that, obviously the simplest answer, just found one on farnell, I obviously need more coffee this morning!

Thanks!

Chris
 

leftyretro

New Member
I future cases where you do have to switch high voltage AC and can't or don't want to use a relay I would suggest looking at optical isolated solid state switches.

They bring a safety factor (typically 3kv isolation between input and output terminals) that is very desirable. They typically turn on with a 3vdc or higher signal and use an internal triac to do the actual AC voltage switching. Some have zero crossing turn on feature. You do have to be aware of their heat sink requirement depending on the AC load current you plan on switching. They come is many sizes depending on current ratings and are cost competitive with electro mechanical relays.

Lefty
 

chris-s

New Member
I future cases where you do have to switch high voltage AC and can't or don't want to use a relay I would suggest looking at optical isolated solid state switches.

They bring a safety factor (typically 3kv isolation between input and output terminals) that is very desirable. They typically turn on with a 3vdc or higher signal and use an internal triac to do the actual AC voltage switching. Some have zero crossing turn on feature. You do have to be aware of their heat sink requirement depending on the AC load current you plan on switching. They come is many sizes depending on current ratings and are cost competitive with electro mechanical relays.

Lefty
Yes, I have a couple of those I thought about using, I do prefer them, but in this situation there is not enough space for the heatsink in the prescribed enclosure.

Thanks anyhow.

Chris
 

Michael 2727

Senior Member
Zero Crossing detects the Zreo voltage point in the
110 -240V AC line and only then turns ON / OFF the
output Triac to switch the load.\
This greatly reduces switching noise as the non zero
crossing types can turn the triac on at any point in
the AC cycle e.g. 5V, 30V, 102V, 195V, 238V etc.
If using non zero types you may need to ad a largish
capacitor to help reduce the noise created.
Large 240VAC capacitors are expensive and bulky.
 
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