# Triac-Diac Dimmer build

I recently bought a DIY 1000W AC motor dimmer meant to be powered off 220-240VAC. I was hoping to use this to control a transformer which in turn powers a heating element.

The heating element needs 60W and i think the resistance is about 5mOhm. My derivation of this is at the bottom. Rather than try get the windings on the transformer perfect i thought using this dimmer control would give me enough flexibility.

This is the circuit that has been supplied:

simulate this circuit – Schematic created using CircuitLab

I am new to triac and diacs but my first question is more about the 1000W rating on this circuit. With my heating element only needing 60W is it a good idea to change the values for some of the resistors and/or caps? or is this 1000W just an absolute max with no relevance to the magnitude of control i would get with a lower powered load?

Secondly, the terminals were not labelled on the diagram and are not labelled on the PCB either. If somebody could figure out the orientation of the IN and OUT terminals i would greatly appreciate it.

Deriving Resistance of the heating element:

• Connected the element in series with a 100 (99.3)Ohm resistor powered by a 4 (3.965)V supply.
• Measured the voltage drop over each of them
• Over element $V_e = 0.2mV$
• Over resistor $V_1 = 3.94V$
• $R_e=V_e * R_1/V_1 =5.05 mOhm$
the 0.2mV drop over the element is very close to the minimal 0.1mV that my DMM is able to measure so i do not know how accurate it is. If anyone knows a better way to test the resistance please let me know.
• P = U^2/R -> P = 230^2/0.005 = cca 10MW!! – Marko Buršič Nov 10 '15 at 8:28
• sorry perhaps i should have made it clearer, the mains power is not going directly to the heating element. it is being stepped down via a transformer so a much lower voltage of about 0.5V. P=0.5^2/0.00505 = 49.5W – Jordan Cartwright Nov 10 '15 at 8:41
• The 1000W is the maximum rating of the dimmer, it is related to the max current the TRIAC can handle. These dimmers usually can work with loads between 20W - 1000 W. No need to change any components ! The transformer might be a problem for the dimmer though, some dimmer don't like inductive loads. But you can just try that, if it works it works and you can use it. The dimmer won't break due to the inductive load. – Bimpelrekkie Nov 10 '15 at 9:11
• You can get a better handle on the resistance by measuring the current through the string and the voltage across the string. That'll give you the resistance of the entire string, and if you subtract the value of the resistor you'll be left with the resistance of the heater. – EM Fields Nov 10 '15 at 9:38