Hi all,
I'm new here, but long time lurker and tinkerer. Hope this is an appropriate spot.
I have used SSR'S in the past without issue.
I have an induction cook top and I have disconnected the coil that does the heating and ran it through the load side of the SSR.
It turns on once on initial signal from the microcontroller signal to the SSR, but when I send a los signal / turn the SSR off. The induction coil keeps getting powered and the SSR doesn't unlatch.
The SSR light goes on and off but the coil remains heating, so I don't believe it's an input / control issue.
The cooktop is 240vac 15Amp.
I haven't just connected into the power button to turn it on and off because I want to pre set the power setting in the cook top board and it doesn't remember it it I turn it off and back on that way. I also don't want to overcomplicate it and write a switch to "push" multiple buttons.
This is because the current and voltage are 90 degrees out of phase with each other. So that when the current drops below the holding threshold the voltage has not dropped below the voltage threshold, and a quarter of a cycle later the reverse happens.
You need some phase angle correction on your inductive load to bring the current and voltage waveforms in phase.
That eBay advert is just for conventional resistive heater elements, not induction systems.
You will not damage anything, there should be phase angle correction as part of your cooker. Otherwise you get to run your heating elements for free. This upsets your power company and it also breaks the law.
It basically involves putting a large high voltage large current capable capacitor, of the right value across your load. These have to be non polarised and are likely to cost way more that your SSR.
Finding the right value is not too easy as you generally can’t measure mains with an oscilloscope without a special and costly isolation probe.
You don’t have to correct it to zero, but somewhere around 30 degrees should be enough for your SSR.
Unfortunately, while I was troubleshooting running it for about 3 minutes, it caused the plastic to start to melt at the heat sink side.
However I tested it with a resistive element and it worked perfectly still luckily.
Oh is there? Could I run a SCR controller at 100% (I have a few spare laying around), which in turn powers the coil or would that cause much badness?
I don't have a oscilloscope or isolation probes and I don't (yet) have the knowledge to introduce a capacitor into this project. But I'm reading to try and understand what you mean better
The next simplest option I can think of in the meantime is SSR>mechanical relay. Unfortunately, however I will have to increase the duty cycle of the relay so it doesn't wear out too quickly or cause issues.
I am not PWM'ing it, however I would have liked to, hence the SSR and which is why I will persist.
There is a clue here, "the heat sink side", it is designed to be clamped onto a heat sink in order to get the maximum rating out of it. To get the maximum rated value you have to have what is called an "infinite" heat sink. In practice this means a heat sink so big ( or force air / liquid cooled ) that it doesn't rise in temperature above the ambient. This is the sort of "trick" that the marketing department play to get a good headline figure. They do it with all sorts of components FETs in particular.
No, the point about using a single SCR is that it can only run at 50%.
Yes, while in principal phase angle correction is simple, in practice the value and characteristics of the capacitor involved are complex to calculate. All heavy users of electricity (industrial) have a meter that measures phase angle. It used to be on a pen recorder but no doubt they have better ways these days. If the phase angle went above a limit even for a few seconds all the electricity in that quarter was charged at a much higher tariff. This provided an industrial user to invest in an automatic phase angle correction system. These were big systems, about the size of a large garden shed and banks of capacitors were switched in and out depending on the current load of the factory and phase angle at any one time.
I think the domestic ovens work on the normal bimetallic thermostat method clicking in and out certain temperatures.
Hi,
To control an induction cooker element you need IGBT type control and current monitoring.
The induction element is designed for 25kHz to 50kHz, much higher frequencies than 50/60Hz, so its impedance will be much lower at 50/60 than at the higher frequencies.
So you will have the rest of the control and power drive circuit.
Look at it and google the part numbers, this will give you an insight into how the element is powered.
Here is one that I repaired for my boss about 3 months ago.
... Before I completely melt this SSR...
