I am converting a toaster oven to an SMD re-flow oven with a prop. and an ssr. can I pwm the ssr or will I need to turn it on and off in short intervals.
Due to the latency and naturally-occurring low-pass filter action in an oven, there is no need to PWM a heating element. Turning it on and off in "short intervals", as you describe it, will provide a more-than-adequate smooth control over temperature.
I was planing to use a 12bit ADC to log the temp from the Thermocouple. I am going to write a program that sends out a pwm signal to the ssr. The micro controller will be programmed check the temp via the ADC if the temp is less than the set temp the micro controller will add 1% to the pwm output wait one second then repeat. If the temp is higher than the set temp the micro controller will -1% from the duty cycle wait 1 sec then repeat.
Am i headed in the right direction? Does any one have any suggestions
No. You'll be cycling it too much. Give yourself a "hysteresis band". For example, if your desired temp is 260F, turn it on when it gets below 258 and off when above 262. That's four degrees of hysteresis, and the way most thermostats work.
Tony,
If you want to avoid the AC circuitry you might try something like this: http://www.makershed.com/PowerSwitch_Tail_II_p/mkps01.htm to turn the entire oven on and off at the power line. It is spec'ed at 100,000 operations at 15 amps. I have not tried this but thought it might be a good component in putting together a "safe" toaster oven SMD reflow conversion kit.
--Ed
Comments
Welcome to the forum!
Due to the latency and naturally-occurring low-pass filter action in an oven, there is no need to PWM a heating element. Turning it on and off in "short intervals", as you describe it, will provide a more-than-adequate smooth control over temperature.
-Phil
http://www.ebay.com/itm/370527117680?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_3893wt_1120
with this Thermocouple
http://www.ebay.com/itm/330594011129?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_3286wt_1110
I was planing to use a 12bit ADC to log the temp from the Thermocouple. I am going to write a program that sends out a pwm signal to the ssr. The micro controller will be programmed check the temp via the ADC if the temp is less than the set temp the micro controller will add 1% to the pwm output wait one second then repeat. If the temp is higher than the set temp the micro controller will -1% from the duty cycle wait 1 sec then repeat.
Am i headed in the right direction? Does any one have any suggestions
-Phil
-Phil
http://forums.parallax.com/showthread.php?134893-need-help-UV-exposure-controller-its-almost-finished
I am planning to do a big write up when i get done.
If you want to avoid the AC circuitry you might try something like this: http://www.makershed.com/PowerSwitch_Tail_II_p/mkps01.htm to turn the entire oven on and off at the power line. It is spec'ed at 100,000 operations at 15 amps. I have not tried this but thought it might be a good component in putting together a "safe" toaster oven SMD reflow conversion kit.
--Ed