Dear all.
I am a hobbyist in need for some advise. First a little bit background and description of my project. I am in need for a very precise temperature control of a large (50L) pot of water. Up till now I have done that with a 2kW ordinary cook top, a PID Controller (REX C100) and a SSR. Works fine, but 2kW is a bit sparse so I have bought an 3.5 kW induction cooker.
The Induction Cooker has a rotary control (potentiometer) with and on / off switch integrated. 4 leaders to the pot, 0V - 5V - center tap and an on / off signal enabling the device.
My take on this, in order to not doing any permanent and physical changes to the cooker, I just disconnect the flat control cable from the mainboard and set in on an 4PDT toggle switch and by that throwing the entire control out to external. By that I can toggle between ordinary and external control.
The PID Controller (REX C100) has a 5V PWM signal, periods adjustable but min. 1 sec.
An second order low pass RC filter (C1-R3-C2-R4) deals with that without too much ripple on the voltage. Somewhat slow in response, but no concern as after all it is 50L of water to change
I have not build the circuit yet, as I am still waiting for some parts, but simulates in LTSpice.
First 'problem'. By opening and measuring the voltage on the control knob, I discovered it is not a 0 - 5V, but rather a 5 - 0V signal. The center tap rests against the 5V side of the pot. at minimum setting. I needed to inverse the signal, and found that best to do before the filter. I uses a transistor (Q1) as a NOT gate, and that seems to be working fine as well. I have access to both 0V and 5V from the cooker, and I uses that on the transistor, no need to build an voltage supply.
Second problem, and here I do need help. It turns out that the minimum power on the induction cooker is 500W. It goes to 500W immediately after enabling the device. Hmmm ... after testing, 500W is enough to slowly, slowly rise the temperature even in this large amount of water, so I do need to implement the on/off function.
What I was hoping to achieve was an accumulation of voltage in C3 from the PWM signal, so that if no pulses had been on for a while, C3 would drain and cutting the on / off line switching the device off. By the first puls from the PID, C3 would charge and opening the line again.
My smoothed signal would be better to use, but that is not so easy, since it is inverse.
I do need some advise her, gentlemen
Regards
Endre
I am a hobbyist in need for some advise. First a little bit background and description of my project. I am in need for a very precise temperature control of a large (50L) pot of water. Up till now I have done that with a 2kW ordinary cook top, a PID Controller (REX C100) and a SSR. Works fine, but 2kW is a bit sparse so I have bought an 3.5 kW induction cooker.
The Induction Cooker has a rotary control (potentiometer) with and on / off switch integrated. 4 leaders to the pot, 0V - 5V - center tap and an on / off signal enabling the device.
My take on this, in order to not doing any permanent and physical changes to the cooker, I just disconnect the flat control cable from the mainboard and set in on an 4PDT toggle switch and by that throwing the entire control out to external. By that I can toggle between ordinary and external control.
The PID Controller (REX C100) has a 5V PWM signal, periods adjustable but min. 1 sec.
An second order low pass RC filter (C1-R3-C2-R4) deals with that without too much ripple on the voltage. Somewhat slow in response, but no concern as after all it is 50L of water to change
I have not build the circuit yet, as I am still waiting for some parts, but simulates in LTSpice.
First 'problem'. By opening and measuring the voltage on the control knob, I discovered it is not a 0 - 5V, but rather a 5 - 0V signal. The center tap rests against the 5V side of the pot. at minimum setting. I needed to inverse the signal, and found that best to do before the filter. I uses a transistor (Q1) as a NOT gate, and that seems to be working fine as well. I have access to both 0V and 5V from the cooker, and I uses that on the transistor, no need to build an voltage supply.
Second problem, and here I do need help. It turns out that the minimum power on the induction cooker is 500W. It goes to 500W immediately after enabling the device. Hmmm ... after testing, 500W is enough to slowly, slowly rise the temperature even in this large amount of water, so I do need to implement the on/off function.
What I was hoping to achieve was an accumulation of voltage in C3 from the PWM signal, so that if no pulses had been on for a while, C3 would drain and cutting the on / off line switching the device off. By the first puls from the PID, C3 would charge and opening the line again.
My smoothed signal would be better to use, but that is not so easy, since it is inverse.
I do need some advise her, gentlemen
Regards
Endre
