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Induction Heating/555 oscillator problem

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louis.haeb

Sun Mar 14 2010, 03:15AM

Registered Member #2646 Joined: Sat Jan 23 2010, 08:27PM
Location: St-Anaclet
Posts: 6

Hi everyone, this is my first post on 4hv.

Recently I got interested in induction heating, and I'd like to build a small heater just to get a feel of how it works. I have seen Paul Peng's project, and it looks like a good place to start. He's using a simple 555 astable oscillator circuit to drive a big MOSFET that controls the current to his work coil. The problem is, he doesn't give much detail, like values of components used. I have read the LM555 datasheet, but the formula they give doesn't make sense to me : with that much variables, I don't know how to solve it for a given value of F. Also, before I buy all the parts, does this design (555 driving mosfet) have a chance to work? For me, it makes sense, but I don't know much about induction heating. I'm not asking to be spoonfed, just a little push to get me started please.

Thank you,
Louis Haeberle

P.S. Sorry for my poor English, it is not my first language. If you wish to point out grammar/spelling mistakes, please do so!

IamSmooth

Sun Mar 14 2010, 07:19AM

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

I'll put in a plug for my web tutorial

Let me know if you have questions after reading it.

louis.haeb

Sun Mar 14 2010, 02:02PM

Registered Member #2646 Joined: Sat Jan 23 2010, 08:27PM
Location: St-Anaclet
Posts: 6

Thank you very much,lots of useful info, wish I'd read that from the start! However, I don't own an (oscilloscope||function generator||inductance meter), so the RC resonance circuit would be very difficult for me to build (I'm looking forward to buy some used testing equipment, but my wallet is a bit thin right now). That's why I was attracted to the 555/MOSFET design, as it loooks like it doesn't require much tooling to set up. I know efficiency is probably far from ideal, and power would be very low, but it is intended to be just a proof of concept. Do you think it has any chance to work at all?

IamSmooth

Sun Mar 14 2010, 07:26PM

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

You really need an oscilloscope.

louis.haeb

Sun Mar 14 2010, 11:06PM

Registered Member #2646 Joined: Sat Jan 23 2010, 08:27PM
Location: St-Anaclet
Posts: 6

You really need an oscilloscope.

Do you mean I should be getting one with the kind of electronnics I'm getting involved with, or that this particular project cannot be made without one? Anyways, I'm planning to get one, but it costs money, which I don't have. Next year maybe...

IamSmooth

Mon Mar 15 2010, 12:33AM

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

There are so many things that can go wrong. You need to be able to see the waveforms, or you will fry chips or blow fuses. You can get some scopes on Ebay for reasonable prices.

louis.haeb

Mon Mar 15 2010, 12:51AM

Registered Member #2646 Joined: Sat Jan 23 2010, 08:27PM
Location: St-Anaclet
Posts: 6

Well, I guess this project is put on hold until I get some money...
Thank you for your help and advice IamSmooth.

Regards,
Louis Haeberle

Mattski

Mon Mar 15 2010, 05:21AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

You could also take a look at the USB scopes that connect to your computer - they tend to be reasonably priced brand new. The maximum signal frequency that they can measure is not as good, but for something like this you will only need a few hundred kHz.

Sometimes you can find companies or university research groups getting rid of test equipment for pennies on the dollar or free, but of course that's kind of hit or miss.

louis.haeb

Mon Mar 15 2010, 09:40PM

Registered Member #2646 Joined: Sat Jan 23 2010, 08:27PM
Location: St-Anaclet
Posts: 6

My father knows a guy who was repairing VCRs and stuff but quit, so he may have some testing equipment to give away / sell at low price, and I will look at my town CEGEP, maybe I'll find something. For the USB scope, unfortunately I am not using Windows but GNU/Linux, which rather narrows the choices to a few expensive units.

Steve Conner

Tue Mar 16 2010, 10:07AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

louis.haeb wrote ...

Do you mean I should be getting one with the kind of electronnics I'm getting involved with, or that this particular project cannot be made without one?

Both! You really need one.

I feel that an analog one is better than the PC-based things. You can pick up a low-end analog scope like the Hitachi V212 on Ebay any day, the kind used in college labs and by TV repair guys.

I've seen quite a few PC-based scopes that work under Linux, though. There's even an app that lets you use your soundcard input, but that's really ghetto.

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