track separation for mains voltages

I'm working on a reflow oven for SMD
circuit pretty much under control
I'm wondering what sort of track separation I should be using for the mains side of the project
(220 volts as I'm in the UK)
any advice much appreciated :slight_smile:

(or will this be my last post!?!)

A few weeks ago there was a fairly long discussion of the subject. Let me know if you can't find the thread.

ah found it thanks
I may well be ok (gulp)

where is the thred be interested in having a look thanks

here’s what I found useful …
http://arduino.cc/forum/index.php/topic,137049.0.html

here's what I've been working on
part of a larger project
this is just the triac section (to turn an oven on and off)

tried it this evening with a neon as oven simulator
220 volts input
switched on and off using the 'duino
works a treat
and all stays nice and cool

have to watch the triac as it's at mains potential
so only finger test for heat when powered off

triac2.jpg

and here's the board layout
grid is .0125"

the opto-isolator has 4.7mm spacing to the ground plane to the rightleft (!)
the power track is 7.2mm from the ground track above

triac3.jpg

What is the purpose of D3 in your circuit? You've drawn it as a diac, but diacs are normally used in phase shift dimmers and speed controllers, in conjunction with a variable resistor and a capacitor. The idea is that at a certain voltage, the diac breaks down and discharges the capacitor into the gate of the triac. I can't see that it serves any useful purpose in the circuit you have drawn.

dc42:
What is the purpose of D3 in your circuit? You've drawn it as a diac, but diacs are normally used in phase shift dimmers and speed controllers, in conjunction with a variable resistor and a capacitor. The idea is that at a certain voltage, the diac breaks down and discharges the capacitor into the gate of the triac. I can't see that it serves any useful purpose in the circuit you have drawn.

er
D3 is actually a diac
one of the application circuits I saw suggested using one
it does seem to work
but I can easily remove it

does the rest of the circuit (with the diode replaced with a wire) look ok?

thanks for looking
cheers
Mike

I've used these optoisolators and just followed the examples in the datasheet, no diac required, as the output side includes a silicon bilateral switch which is similar to a diac.

The rest of the circuit looks OK to me. As the load is resistive, you could use a zero crossing opto triac such as MOC3042 instead of a random fire one, which would create less mains borne interference. But unless the heating element takes a lot of power, it's probably not necessary.

Yes, D3 is clearly redundant, since thats an optical diac in the coupler.

Is there any reason you opted to build your own versus use a Solid State Relay?

You can get a ready to use 10 AMP SSR from MPJA http://www.mpja.com/, for example, for as little as $7.95.

SSRs cost a little more in the UK, however Farnell has a 1.2A one for £1.87 and a 2A one for £6.34, is that is enough for your heating element.

dc42:
The rest of the circuit looks OK to me. As the load is resistive, you could use a zero crossing opto triac such as MOC3042 instead of a random fire one, which would create less mains borne interference. But unless the heating element takes a lot of power, it’s probably not necessary.

:slight_smile: thanks
total power is only 1 kW (4.5 amps or so at 220 volts)
seems I’m actually using a MOC3080X - which is zero crossing :slight_smile:

pwillard:
Yes, D3 is clearly redundant, since thats an optical diac in the coupler.

Is there any reason you opted to build your own versus use a Solid State Relay?

You can get a ready to use 10 AMP SSR from MPJA http://www.mpja.com/, for example, for as little as $7.95.

parts cost < £1, SSR > £10
easy choice really - I’m a cheapskate by trade :slight_smile:
no major reason other than it’s part of a larger project
I’ll have a look at what’s available on this side of the puddle