Turning a smoke machine on/off with a triac

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- 6th January 2011, 18:39
The Master

Turning a smoke machine on/off with a triac

Hi, For a while now I've been using PICs/optos/triacs to activate smoke machines. I would like to know though if its possible (or safe) to turn the power to the entire machine on/off. Instead of just the pump motor I will be controlling the huge heating coil aswell.

My smoke machines are in the range of 700-800W 240V. I work that out to be 3.3A max. The triacs I've been using to control the motors are capable of switching 8A at 600V. That sounds perfectly safe to me but as I usually stick to low voltage and its a big coil instead of a simple bulb I would like a second opinion.
- 6th January 2011, 23:35
mister_e

Most commercial model I know and see on my workbench each months just use a Relay for the Heater but a Triac for the pump (obviously for flow/burst control). If your control is not fancy, you could just use relays, but if you manage the heater temp, the smoke flow/burst, current limit, etc etc... then TRIACs (BTA serie with built-in snubbers) are the obvious choice.
- 7th January 2011, 14:31
The Master

Ok, Thanks. I will go with the triac then. I'm using BTA already so thats good.

I did think about using a relay but I've used those in the past for the pump motor and they cause all nearby PICs to reset (I had a post on here a few years ago about it). The solution was to use triacs. I've used diodes in the past on the low voltage side of relays to stop current flowing backwards. Maybe something like that on the high voltage side would fix the problem but I would rather use a triac instead.
- 7th January 2011, 15:54
ardhuru

A triac would be fine. Even better, add a few lines to detect the zero crossing, and switch on right after that. That should reduce the inrush current.

Regards,

Anand
- 7th January 2011, 17:30
The Master

Good idea. I have at least 1 pin spare on the PIC. I'll do the same for the pump too
- 9th January 2011, 14:16
keithdoxey

Quote:

Originally Posted by ardhuru

A triac would be fine. Even better, add a few lines to detect the zero crossing, and switch on right after that. That should reduce the inrush current.

Regards,

Anand

Or drive the triac with an opto isolator that includes zero crossing detection. :)