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Switching Heater Elements at Low Voltage
I’ve been having a think about power control and the possibility of spitting a single heating element into two unequal parts for more control options. It’s definitely overkill, and could be plain wrong, but it has some potential advantages:1) 2 independantly switchable ‘elements’ that are still under SCR control, but in a single element package2) SCR doesn’t have to work so hard when controlling lower power output3) Switching is not at domestic supply voltageDisadvantages:1) More complexity – could just wire up all links in the element and control it as one on the SCR2) Needs 4 core cable from the element3) Power density impact?4) It’s completely not necessary!This is just a circuit diagram. Naturally, all the control elements and fan would be in a single enclosure. Any thoughts on this just as a simple musing?
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5 Replies
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That looks like one of the single / three phase elements that I have. Three separate coils which can be wired individually or linked. I used to use mine with an SCR over one element and switches to control the other two. This gave a smoother range of control from the SCR (0-1500W as apposed to 0-4500W in the same movement). With your circuit, the jumps when switching in or out elements will be smaller, but still significant.For a slightly greater cost, but final simplicity and more control I’d love to have a microcontroller controlling 3 SSRs using a low frequency PWM approach to switch each element on and off over a 2 second window. By running all three elements it’s possible to balance the load across all three elements. This is as you point out “completely not necessary!”. One advantage of controlling all three elements with an SCR (or SSVR) is that at low power levels you have a really low watt density.Never let that be a stopping point. If a thing is worth doing, it’s worth doing excessively and for little reason!”I have a potstill that smears like a fresh plowed coon on the highway” – JimboA little spoon feeding *For New & Novice Distillers
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Kinda over complicating things. Use switches rated to handle the heater current and do away with the relays.Use an AC fan and do away the 12vdc power supply.
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Indeed, it’s quite daft to use relays really. Was just an idea. One thing I’m not totally sure about is whether an SCR is happy to be powered up with no load connected. Does anyone know? If both sides of the element are turned off, I want it to be safe. With a 3kw element, I might just wire the 2kw segment to the scr with no switch and have the 1kw switchable but bypassing the scr, which gives me a ‘booster’, plus a master switch for the whole box.
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The SCR (triac controller) will be just fine with no load connected .My recommended goto .wiki/index.ph … ion_Theory
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Volt meter and knob on the pot won’t agree.SSVR wouldn’t mind in the least if there’s no load.
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