The idea is to control the induction heater to heat up a piece of metal to a certain temperature, use the temperature sensor as a feedback to be able to maintain the temperature.
The idea is to later on make heating curves where for example, the temperature would get hot in the begin and slowly cool down or the opposite of starting slow and increasing with time.
Currently my issue is with the ZVS induction heater. There isn't a lot of information on it that's easily available or understandable to me.
I've seen posts of people saying a very low PWM frequency is required, I've seen posts about only using very high frequency, I've seen high frequency + smoothing capacity, and I've seen posts of people saying you can't use PWM at all and you should only use interval heating. Thing is, these are conflicting and I can't really find anyone backing up what they're saying so I'm not sure if this is the actual case or not.
I know that interval heating will probably work, but it won't let me maintain the temperature accurately.
Any suggestions for things I can do? I'm hoping I don't do something mindlessly and end up frying my components.
Lots of words, but no report on your actual tests of the heater. Quit searching and begin your own tests. You have not told about your power supply for the system. Measuring temperature should be the last step in your development.
I think that you need to make a variable power supply so your Arduino can change the voltage between 5 and 12V. It appears that at 12V it draws 10A (120w) and at 5V it draws 6A (30W). That should give you a good range of heating.
I have a 12V powersupply. Can't remember what the power rating for it but it was more than 10A for sure.
I didn't ask anything about the sensor, just mentioned it to give the full picture of the project. I was hoping to not test anything before I know what I'm doing so I don't end up frying my components. That's why I asked to see if someone is more knowledgeable than me that can confirm any of the things I'm confused about.
I'm looking to make a small device that I can eventually make portable and power through batteries. So that's not really an option. If that's realistically my only option, then I will switch to interval heating which I know will work and satisfy my limitations but won't achieve the output/accuracy I'm aiming for.
Do you have an idea of how long you need the battery to last to be useful? Do you need it to run for hours between charges or seconds?
One hour at full power is 10Ah. You can get a 12V 10Ah Lithium Iron Phosphate battery for about $40. It weighs about 2.7 pounds (1.2 Kg). Will that be light enough and have enough run time?
I can share this much with you. A Google of "ZVS Induction Heater Schematic" will bring up dozens of circuit diagrams. The unit you linked to rated for 12 volts will draw about 10 Amps. This is a unit I played around with for annealing brass cartridge case necks.
I do not suggest using PWM and the reasoning is this. Power applied should be instant The applied power needs to immediately start oscillation. Failing that one MOSFET will go into conduction before the other and remain in that condition. Eventually you will smell smoke and your module is dead. Pictured is a 1 KW unit and needs a minimum of 12 VDC to start and can be run up to 48 VDC drawing major current. About 20 Amps if I recall correctly.
The unit you linked to is a 5 volt (60 watt) to 12 volt (120 watt) unit. I can tell you while I have no idea what you expect for heat that 120 watts will heat the tip of a small screwdriver but I doubt cherry red. When I was using the one I had I either powered it or it was off. I timed the power on. What I cobbled together worked but really annealing my brass wasn't getting me much so I just stopped. Using Google I did find several good articles on induction heating.
During my initial trial and error I spot welded a few small thermocouples inside my case necks and used a data logger to watch temp rise and fall to get my timing right. As to understanding what's out there feel free to ask questions as your project moves along.
I forgot to mention when I was playing around with this stuff I came across this link which has plenty of useful information. There are others but this one is a good read and hopefully will answer some of your questions.
Thanks for your reply! I was thinking something that is hand held. I would be heating a device, without getting too much into the device since it's not related to this forum. But basically, I would run the induction heater for 30 seconds total per use. For around 10 uses or so. So I was thinking something around 3 Li ion 18650 cells.
That being said, the portability part is not currently the main focus. The main focus is to get a functioning heater and then I can improve it later.
EDIT: also, I have a variable voltage DC to DC, but this manually changed, I want to have it controlled through the arduino though.
From my limited understanding, I think what you're saying is pretty spot on to what I'm finding so far. I'm starting off with a very low frequency of 0.5Hz. Similar to interval heating. I've read people getting it to work with up to 1 Hz frequency, not sure if I can push it further. I've also seen people using a "heart beat rate", honestly confused if they mean 1Hz or up to 1.5Hz maybe? That being said, I'll start off with this and see how accurately I can do temperature control. It won't be what I want, but I'll start with this.
As you said, it's a pretty weak system, that's supposed to heat up the tip of something the size of a hollow steel pen. And it should only heat it to around 200 degrees C. So it should be more than enough heat for the system. I'm just trying to see if I can change the heating curve. Instead of going straight to 200, I want to to slowly ramp maybe and plateau at a certain temperature for a while before increasing to 200. And when it does, I don't want it to exceed 200 by much. That's the idea at least.
I've seen people suggesting a smoothing capacitor, a hold up capacitor and something called a gate drive circuit? Honestly, as I said this is beyond my electronics knowledge. My background is mechanical and I took just some intro to electronics courses. So I need to research these and see what can help me achieve what I'm looking for if any. I've posted this on another forum where it seems there are people that have tried standard PWM signals and didn't reach anything. They didn't fry their devices though so that's good. In the end, maybe I won't be able to achieve this at all and I'll just stick to the 1Hz frequency that seems to work for now.
For now I would not give any thought to smoothing capacitors, hold up capacitors or anything gate drive. The ZVS module you linked to is designed around 5 to 12 volts. You can try starting with about 6 volts. Using a simple On/Off switch I would power it up and see what you get for heat on whatever it is you are induction heating. Typically induction heating is done in a frequency range of about 1.2 to 10 KHz.
In heating applications this is commonly called ramp and soak. We slowly ramp up to a temperature and stop (soak period) then continue to ramp and soak for given periods till we achieve our set point. The ramp and soak stages are known as the profile. When you hit set point anything above is overshoot and you want to keep overshoot at a minimum.
My read with the 1.0 Hz or 0.5 Hz is you are pulsing your ZVS at those rates. Assuming a 50% duty cycle and 1.0 Hz your heat is on for 0.5 seconds and off for 0.5 seconds. You could drive your ZVS circuit with a MOSFET gating it On and Off. Thus I can see where "gate" can figure in. Temperature control can be along the lines of what is called proportional integral derivative which is just a fancy way of saying as we get close to our set point our pulse (On/Off) times change. When properly tuned there will be little or no overshoot of your set point. A Google of PID control will get you some good explanations.
