Electronics > Beginners
Mixing resistive heating with inductive heating?
rwgast_lowlevellogicdesin:
Im not saying induction heating is not caused by the resistance in the coil, maybe a better title should have been conducion heating mixed with convection? As far as raising the resistance of the coil using kanthal/nichrome etc... im not sure why that would't make more heat, the coil itself shows resistance when it is tanked and loaded with AC current, but adding a true resitive element such as nichrome should produce more heat faster I would think. Non inductive, i.e resitive only elements, will dump there heat in the same manner regardless of dc, ac, hf ac, microwaves etc.. I cant figure out where I read it, so I dont know if I misunderstood but isnt the coils power calculated by something like current^2 times resistance, which means raising the overall resistance not just the impeadence should produce more power?
Sadly even if I am correct about this im sure the idea is not very practical, as stated above keeping the coil cool so it doesn't deform and short causing a melt down is sometime the bigger task than the heating, using thinly gauged heating wire would probably blow a hole through itself fairly quickly, but maybe if the two were used at a lower power they could get to temperature quicker as long as the temperature isn't to hot. Maybe even better the work piece could be wrapped in fairly light gauge quick heating resistive wire, and an induction coil could be used not only to heat the work but pump extra heat in to the already powered nichrome/kanthal?
Like I said i am no expert on this stuff at all, and these ideas could be just plain BAD, not just in a practical way but the theory also. Im sure if they would good ideas someone would have done it and written a paper about it by now, i mean induction heating has been used since the 1940's... Im just hoping someone can explain to me why its not done....
Berni:
Well if you want more heating power you simply push more power into the inductive heating coil and the heating target will heat up faster.
The heating caused by the resistance dissipating power just the same as inducing a heating current in the heating target. They both sap away power from the LC cirucit, its just that where the power is turning into heat was moved from the target inside the coil into the coil itself. No extra heat is generated, just the place where the heat is generated is moved from the inductive heating target to the coil. But heat generated in the coil needs to still travel to the target somehow (And some of it will travel in the wrong direction towards the outside and be lost to the enviorment) while the heat generated in the target is already where it is supposed to be.
So ideally to make it most efficient and fastest to heat up you would want a superconducting coil so that all power that is being input ends up dissipating in the target where you want it and none on the coil. That way there is no chance for heat to get lost to the environment (apart from the targets own loss) and you have less mass to heat up since the coil does not need to get up to temperature, just the target.
There is no real limit to how much power can be input with inductive heating. With a resistive heating element you are limited to how much temperature the element can get up to before it melts. But with inductive heating you can theoretically input 100kW of power as long as the coil is kept cool enough (By being so conductive it doesn't get hot, or actively cooling it with water) and get the heating target glowing red hot within a second. This is the reason for using inductive heating in the first place, it magically causes heat to appear inside the heating target rather than making the environment around the target hot and waiting for the heat to propagate into your target (And this is very limiting due to how slowly heat propagates).
So if you want your inductive soldering iron to heat up faster you simply need to hook it up to a bigger RF power supply and be careful not to pump so much power into it that the copper coil melts (But hey you do get the maximum amount of resistive heating that you wanted since the coil is glowing red hot).
T3sl4co1l:
Does anyone actually make an iron that's induction heated without using Curie temp stabilization?
The advantage would be that you can deposit heat in the tip without incurring the temperature drop and time constant that convection/radiation from a heater gets.
Downside is, you need active cooling on the coil to keep it coil...y, otherwise it's going to get at least as hot as the tip, and then you still get the temp drop and time constant, just at a lower order (a pole-zero response I suppose).
Needless to say, coil efficiency drops severely with temperature, because copper has a huge tempco. You might not be able to use copper at all, in which case the efficiency is that much lower to begin with (though the tempco can be lower, so at least the efficiency is flat). And then you're that much closer to the original resistive-heat case, and there's some Q factor where you need to ask, why bother?
(Q factor roughly being in terms of, say, unloaded coil Q, which if it's 1 or 2, isn't much magnetic field, regardless of what you put around it. If it's 10 or 100, it's probably going to be a reasonable fraction due to induction. Presumably your coil coupling will be excellent, so that even a low Q could potentially have quite reasonable efficiency. But if it's 1 or less, even that won't help you.)
As for the power supply, I would assume a variable frequency drive is fine in this case, and that you have a shielded or balanced cable supplying power to the iron. For low Qs, an off-the-shelf resonant controller will do, probably with a transformer to adapt to the coil impedance. (The resonant cap can be onboard, or possibly in the iron if there's room.) For higher Q (more than maybe 5 or so), a slower controller may be desirable, like a PLL+VCO. This may not be as feasible using OTS controllers (that tend to have intentional quirks, which improve regulation or efficiency in traditional topologies like LLC), but a CD4046 or the like, can be used with a little glue logic, to good effect.
If constant frequency is desirable, that's probably fine too, and can even be direct drive (nonresonant) up to modest Q. (The downside to nonresonant is, if you're delivering say 100W at a Q or 10, that's 1kVA the cable, inverter and bypass caps need to handle. They don't know any better, they think you're making 1kW. So they need to be that much higher efficiency, and costs go up very quickly. We're already talking boutique quantity and pricing, so I assume there's a little budget for that, if it should prove useful.)
Tim
rwgast_lowlevellogicdesin:
Awesome thank you Berni, this is exactly what I had wanted to know
Im not even sure if I will ever attempt to really convert a 907 handle to induction but I got the idea from this blog post when searching around
https://hackaday.com/2017/06/01/diy-induction-soldering-iron/
I also know there are a few inductive based stations with temperature control that do no use curie point. One is made by quick and can be bought in US 120vac format rebranded and sold by some online tool vendor handytool or something, I would have to do some history searches to get the correct vendor site. Anyways this is the 220Vac version on Amazon
https://www.amazon.com/Quick-Induction-Lead-Free-Soldering-Station/dp/B00YUQ4MZE
I am acually considering buying this station, it was $140 on the site I mentioned, but they only sell four tips and im just not sure its worth it when you can get a decent cartridge station for a little more.
The other one is an atten AT306DH which I just can not find a seller for, all the ali express links are broken. There is a picture on this page if anyone is interested
It is listed as a 90W HF powered station, atten is crap anyways and that is why im just building a station.
My idea if I ever were to do it is to just take a regular old 900m style tip and stick a rod made of ferrous metal in the tips hole along with thermocouple, you know the hole where the ceramic heater would usually go, then use an OA torch to braze the rod in to the hole, that joint and filler is good to 1800F much higher than solder temps. Lastly wrap the rod in kapton like in the hackaday video and slide the coil around it as far up the rod as close to the tip as possible and hope it all fit with in the original hakko 907 sleeve :). Not saying this will give a JBC a run for its money but this should be far superior to a ceramic heater iron with the thermo couple so close to the tip, and the speed/accuracy of induction. Hell why not just use small copper piping and a little medical DC pump to water cool the thing.. lol probably not.
I just thought of something, if you dont own a gas welder and dont want to spend $400 on one, you could do this on the cheap without the Oxy Actelyne even, just have to ebay a cheap induction coil kit that gets hot enough to melt the brazing rod!
Jwillis:
There is a review on you tube about the Quick 202D, but by looking at the video I can tell the person couldn't operate a BIC lighter without issues. Try reading a manual .The problems pointed out are frivolous and didn't even put the thing to work to see how it performed.
The Quick products are pretty good . I have the QUICK861DW hot air rework station and QUICK TS 1200 Soldering station. Both heat up really fast and have excellent temperature stability. I did look at the 202D but settled for higher watts on the TS 1200 although its not a HF soldering station. The only problem I had was with the tips. The TSS02 tips are more expensive and the T12 tips won't fit the handle.
Other that that I'm very pleased with the Quick products.
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