LC Parallel induction heater question / Electromagnetic Radiation / Forums

Forums

4hv.org :: Forums :: Electromagnetic Radiation

« Previous topic | Next topic »

LC Parallel induction heater question

previous 1 2 3 next

Move Thread

LAN_403

Thomas

Wed Apr 27 2011, 04:40PM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

Quick question, but on the half bridges why is no one using a capacitor divider?
If I were to remove the dc blocking capacitor and connect Lr and Cr in parallel. Then connect one end to the half bridge output and the other end to the capacitor divider. This shouldn't alter the resonant frequency and dc still will be blocked. This should also be more stable.

James

Wed Apr 27 2011, 05:29PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Thomas wrote ...

James wrote ...

That's probably a bit small as far as current capacity goes. Why don't you wind one yourself? Seems like I saw someone using a spool of wire as an air core inductor for something like this. You could also make one with a salvaged ferrite core. Choke is just another name for inductor.

Oh my capacitance is small because I'm not using a matching network at the moment. Right now its resonating at 205kHz.

Once I add a matching inductor I'll increase the capacitance. Not sure how much though. I guess for now I'll copy Rich's design in terms of values.
I could make a air core inductor, but I don't have enough cabling. I prolly need like 60 ft or so of 16awg.

Capacity, not capacitance. In other words the current rating of the inductor, nothing to do with the capacitors.

Thomas

Wed Apr 27 2011, 06:57PM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

James wrote ...

Thomas wrote ...

Capacity, not capacitance. In other words the current rating of the inductor, nothing to do with the capacitors.

I'm sorry I'm not following. I should pick a inductor (Lm) based on the impedance of the Lr and Cr?

James

Wed Apr 27 2011, 07:14PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Inductors have a current rating. If you put more current through an inductor than it is rated to handle, it will saturate or overheat.

My favorite resource for induction heating is this

He presents two complete working designs that are both quite simple. I built one based on the Royer design and it works as presented.

Thomas

Thu Apr 28 2011, 02:16PM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

James wrote ...

Inductors have a current rating. If you put more current through an inductor than it is rated to handle, it will saturate or overheat.

My favorite resource for induction heating is this

He presents two complete working designs that are both quite simple. I built one based on the Royer design and it works as presented.

So the matching inductor is based on the current draw of Lr and Cr?
The what about the matching capacitor?

IamSmooth

Sat Apr 30 2011, 07:12PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Have you read this?

It is a different topology, but it is very simple.

Thomas

Sun May 01 2011, 09:05PM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

Hi there
The link doesn't work.

Oh I have one other questions question.

1. My heater can heat stuff to about 400F. I can't break that. I noticed that my matching inductor gets super hot and there's also a very large voltage drop across it. Should I decrease the inductor or increase. My gut is telling my decearse. Decreasing L-Match means more power in the Work Coil right?

Thomas

Mon May 02 2011, 02:51AM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

Oh wait does the inductor generate a larger than the input voltage.
I'm pretty should that this will happen.
The smaller the inductor the lower the voltage. Therefore the current in the work coil will be lower.
the Higher the inductor value the higher the voltage in the work coil.

So either more input voltage or more inductor will produce more current draw and create more heat.

Right?
I'm pretty sure my math is write.

IamSmooth

Mon May 02 2011, 03:00AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Try this link

You are going to have a lot of current flowing through your inductor. If it is getting hot the first question is what is getting hot: the core, the wire or both. I use ferrite cores for my inductor and I give the source in my link. If the wire is getting hot you can use thicker gauge or switch to litz (or make your own). If you lower your frequency the wire will get less hot as there will be more copper conducting the current.

You can't get above a certain temperature because you are not feeding more current into the tank. You need a higher input voltage.

The work coil geometry will also affect your induced voltage in the workpiece. The more turns the less voltage; the larger the coil, the weaker the field. Of course, other issues come into play like quenching if your coil gets too tight.

IamSmooth

Mon May 02 2011, 03:24AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I also want to point out that I think your blocking capacitor is not set up correctly. According to your schematic, current is only flowing during one cycle. If the top feet is open current flows through it into the tank. When the top switch is closed and the bottom one is open you just short the tank.

You can get more out if you reverse the polarity by using two blocking capacitors. When the switches open and close the voltage that energizes the tank is reversed.

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob