Induction heater coil question

[dandare99]

can anyone help me out? i need to wind a coil for my induction heater and want to use 1/2in copper tube. i know that im not supposed to go under 85uH. can someone please help me out with a formula to detirmine the amount of turms i will need? the coil should be 2 in in diameter and about 5 in long, but i do not seem to be able to find a formula to determine the inductance of a coil that is made from copper tubing

the max ampreres i can use is 20A
Freq -+100KHz
Rail suppluy +150/-150V
thanks guys

 

[Optikon]

can anyone help me out? i need to wind a coil for my induction heater and want to use 1/2in copper tube. i know that im not supposed to go under 85uH. can someone please help me out with a formula to detirmine the amount of turms i will need? the coil should be 2 in in diameter and about 5 in long, but i do not seem to be able to find a formula to determine the inductance of a coil that is made from copper tubing

thanks guys

2" in diameter and 5" long are very comparable dimensions. is the 5" the coil height? or is the total tube length 5"? If the tube length is 5", it doesnt seem likely you'll achieve anything near 85uH if the dielectric is air.

Please specify your constraints in ALL 3 dimensions.

There are standard formulas for computing inductance based on geometry. But these may not apply for a diameter that is very close to the same total length (2" & 5" are close)

At high frequencies, there is an effect called proximity effect that may allow you to calculate using an equivalent surface area of your tube and using the standard solid-wire formulas provided they are still valid for your dimensions and operating frequency - you need to check that.

On that note, I can check my library for this kind of information. I have some text books on industrial heating design which covers induction heating. I can see if there is something relevant in there. Otherwise, you may have to derive the formula yourself (which is not too hard) from first principles.

 

[Leftyretro]

can anyone help me out? i need to wind a coil for my induction heater and want to use 1/2in copper tube. i know that im not supposed to go under 85uH. can someone please help me out with a formula to detirmine the amount of turms i will need? the coil should be 2 in in diameter and about 5 in long, but i do not seem to be able to find a formula to determine the inductance of a coil that is made from copper tubing

the max ampreres i can use is 20A
Freq -+100KHz
Rail suppluy +150/-150V
thanks guys

Well if it was me I would just go a head and wind the tubing using your 2" OD requirement with as many turns as fits in 5" of length, leaving say 1/4" spacing between turns and then measure the inductance. From there you can see if you need less turns or if your going to have to increase the 5" length or the 2" OD. With that kind of current and power your going to have to measure the inductance sooner or later before applying full power to the inductor, rather then just trusting some calculation or program alone.

With that kind of material, 1/2" copper tubing, you don't want to come up short of inductance as it's far easer to remove turns then to try and add turns...
Lefty

 

[Russlk]

Your requirements are completely impossible. I calculate that 21 turns on a 12 inch diameter form, spread over 15 inches length will give 85 uH.

 

[Sceadwian]

It's 20amps, why not use something a little more sensible like 12 gauge wire?

 

[Optikon]

It's 20amps, why not use something a little more sensible like 12 gauge wire?

In some heating applications, the coil must be cooled with water so in many cases, using copper tube makes alot of sense. However, the OP has indicated some ridiculous size tube IMHO for the power levels it looks like he is working with.. so I dunno.

 

[Sceadwian]

From the OP's specs something like 1/16th inch thin wall copper tube might be better if liquid cooling is wanted.