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trouble with a triac
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1makermold:
I was thinking about the same thing, but I need the circuit go into a small space, and I don't thing a small reed relay could handle 5-6 amps, plus to expensive
Zero999:
I think the idea is to use the reed relay to trigger the TRIAC, not drive the load directly.

Lots of reed relays aren't isolated enough to protect against electric shock, but that's a non-issue here, assuming the 24V or trigger circuit aren't floating at hazardous voltages i.e. are both isolated from the mains.

I think an opto-coupler and TRIAC is a good idea. The only alternative, other than a relay, is a MOSFET solid state relay, consisting of two back-to-back MOSFETs and a photovoltaic opto-coupler, such as the VOM1271, but it's more expensive.
Doctorandus_P:
Triac's are not symmetrical devices.
Most can be triggered in 4 quadrants, but one of the quadrants is always worse then the other three, and you are using it in the "bad" quadrant.

Combined with your low output voltage It is likely that your triac only is triggered in one direction, and this explains why you measure half the voltage.

Maybe you can get it to work with lowerint ge value of the resistor, so the triac has more gate current. You could also make a tap of the 24V before the load, and use a diode and capacitor to buffer it to generate a  voltage to trigger the triac. If you build this circuit in such a way that it pulls current out of the gate instead of pushing it in, you also avoid the "bad" quadrant.
1makermold:
I did lower that resistor, but Im not sure how much lower I should go
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