for example on my mypin td4 pid, when in manual mode and set to 50% power.. the element is on for half a second then off for half a second ... pulsing, this never allows the element to get hotter than half power would allow.
the ssr just pulses the power on and off at a certain fast rate determined by the cycle time setpoint of the pid.. I dont believe ac cycle time has much to do with it really its not pulsing it that fast. perhaps someone more knowledgeable will clarify. if the pid cycle setpoint is set for 2 second than in 50% manual mode the pid would power the element for 1 second then off for one second at least thats how it appeared to work on my mypin pids.
Ok but I asked mainly to understand if you were asking and considering this venture because you didnt understand it was really unecessary and how the normal method 95% of us use already controls the heat output and that its already easily done natively with adrduinos hardware and a simple ssr. Your questions above and in the omron thread also eluded to you not understanding how the on off switching already controlled heat output in a steady linear fashion like your describing.
No you havent, sorry I'm lousy at communicating online. I just felt that you weren't understanding the importance of your intentions and how they matter and factor in to how informative and clear the thread plays out for everyone involved is all.
You cannot control an AC powered heater without on/off pulsing. The AC voltage and current go to zero 120 times a second (in the USA), which means at those points the element is off. Phase angle power control, is still on/off switching, but at a cycle time of 8.33 msec. So, everything discussed so far in this thread is still on/off pulsing. The only thing changing is the cycle time, which for the options discussed varies from 8.33 msec up to 2 sec.
You cannot control an AC powered heater without on/off pulsing. The AC voltage and current go to zero 120 times a second (in the USA), which means at those points the element is off. Phase angle power control, is still on/off switching, but at a cycle time of 8.33 msec. So, everything discussed so far in this thread is still on/off pulsing. The only thing changing is the cycle time, which for the options discussed varies from 8.33 msec up to 2 sec.
The only way to get zero on/off pulsing is to use a controlled output voltage DC power supply. If you want to go this way, a switching power supply is much more efficient than a linear supply (I don't even know if you can find a linear supply at ~5500W.)
Looking for a solution implies that there is a problem that needs to be solved. Many of the replies to this thread are asking what is the actual problem that needs to be solved, and noting that there is no real unsolved problem related to powering heating elements in homebrewing applications. One of the basic tenants of engineering is that if you don't understand and state the problem correctly, you are very unlikely to find a good solution.
Brew on
Even a saturable core reactor uses AC and so is subject to the microseconds of off time when current goes through 0 at the end of each half cycle. Now a three phase saturable core reactor followed by a bridge rectifier would give you reasonably smooth (low ripple) DC with no zero crossings. So would a single phase rectifier with a capacitor to "fill in" near the 0 crossings. So would a linear power supply with a regulator (we want control here too) but we eschew those because of the power loss in the series pass transistor. How about a switching power supply? Much more efficient and also regulates?
In it's simplest form, a switching power supply is just a bridge rectifier on the AC input, followed by some filtering, followed by a pulse width modulator, and finally more filtering. There is also a feedback circuit that monitors the output voltage and feeds an adjustment signal to the PWM to maintain the desired output voltage. The interesting thing about the switching power supply is that instead of PWM working at 8.33 msec cycle time, or slower, the PWM works with cycle times from about 100 micro sec (10 kHz) to 1 micro sec (1 MHz.) The higher frequency operation allows the use of smaller capacitors and inductors in the output filter circuit to obtain a given amount of output ripple.
Can you please state for the record why you want to avoid rapid switching? We all want to know If you have an interesting end goal or just didnt know that rapid switching is the way this is done and that there are no function downside.
This may be where you are hung up. The goal isn't really constant drive power to the element at all. It is constant heat delivery to the load (wort). Constant heat is indeed impossible but we can approximate it sufficiently closely by supplying pulses of heat as long as they are sufficiently closely spaced such that a plot of temperature vs time is not discernibly different from a sloped straight line until boiling is reached after which we want boiling to be continuously maintained at a uniform level of vigour.
