SCR?


 

Darren L

TVWBB Member
Has anyone tried to condition the fan voltage to drive an SCR? I'm trying to find a way to use the Heatermeter to control an electric element. I think it will work if I can condition the voltage to a 4-20mA, 0-10v etc. signal. To be honest I haven't dug too deep into this or done the search yet, so I apologize if this is a worn topic.
 

MartinB

TVWBB Pro
I think phidgets makes what you need.
They sell a V in to pwm out , to power scr. They sell the scr too. But you may not want to use laptop, phidget setup, etc.

If hm fan setting is on pulse, that might work to switch a scr , providing a % on time related to output?

You can buy an inexpensive PID controller that can power an scr directly as well. Yeah, not heatermeter.
 
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Do you mean an SSR? Solid State Relay? If so, then yes, I am doing it. It works out of the box but there was a setting you had to make on the AVR so it would not PWM, I want to say it did a 10 second time interval and so the at 60% power, it would turn the relay on for 6 seconds, then off 4.
 

Bryan Mayland

TVWBB Hall of Fame
Do you mean an SSR? Solid State Relay? If so, then yes, I am doing it. It works out of the box but there was a setting you had to make on the AVR so it would not PWM, I want to say it did a 10 second time interval and so the at 60% power, it would turn the relay on for 6 seconds, then off 4.
Yeah if you want a 1/10Hz (10 second period) on/off output at 12V, set the HeaterMeter output mode to "Pulse" and set the min to 100%. Then it won't do a 490Hz PWM it will run proportionally to the output requested so 65% would be on for 6.5 seconds and off for 3.5 seconds then repeat.

I've never used an SCR by itself though and I think most SSRs use TRIACs? Question mark because I am not sure. If you want 0V-10V output you can just power the HeaterMeter with 10V input. It passes whatever the input voltage is to the Blower output in Pulse mode. Internally we step down the input voltage to 5V so anything over 6V is fine.

Because there is an inductor and capacitor on the output, the edges of the on/off waveform have a lot of rise and fall time but SSRs don't seem to mind because the period is near-infinitely long. If you need a more crisp edges, short out the 200u inductor and replace the 47u/25V capacitor with a 10k-100k resistor (or leave it off, the LED in the SSR is enough to sink the current).
 

Darren L

TVWBB Member
Great information. Thanks. It sounds like a 10v supply is my answer. The type of SCR I'm considering is phase fired and would vary the output power to the element based on an analog input value. I.e. 0-10 volts in would be 0-100% out. This will give an analog control of the element instead of an on/off pulse. With this setup I can smoothly control a 120 or 240v oven element. I can also set limits to the max output, current, etc. I can easily do this with a PID controller, but I can't match the heatermeter functionality. Alarm responses, graphing, networking, the list goes on. This whole project is just to make summer sausage and other low temp smokes. Well... and to try something new.
 

Bryan Mayland

TVWBB Hall of Fame
Ooh if you're looking for a 0-10V analog output from the HeaterMeter, then what I've described isn't going to get you there. I described a 0V and 10V output that's either on or off for up to 10 seconds at a time.

If you want a 0-10V analog output, put the HeaterMeter in Pulse mode with a 10V power supply and run with normal fan settings (min=0%). That gives you a 0-10V PWM signal at 490Hz. Now replace the 220u inductor with ~100ohm resistor. This will form a low pass filter with the 47u/25V capacitor which _should_ give you an analog 0-10V output with fairly low ripple. I'm not sure about that, you may need to find just the right resistor to match the input impedance of the SCR. I haven't ever tried anything like this but it is theoretically possible. It may need to replace the diode there with a resistor to ground too... not sure without being able to try it myself.
 

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