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  #1  
Old 01-25-2012, 05:14 PM
storken storken is offline
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Default Induction heater help

Long time lurker, first time poster. Second year electrical engineer.

Long story short: I'm building a vacuum induction forge.

I've built my vacuum chamber, it's able to pull all the way down to 0.1mbar using a rotary vane pump. I havent started building my induction heater yet, but here are my avatible materials.

- 100x 1.8uf panasonic film capacitors. 400V
- 100x 0.1uf MLCC ceramic capacitors. SMD. 100V.
- Copper tubing (~10mm) for the inductor. *
- Atmel AVR 328
- Arduino (I've got several)
- 8x IRFP2907 N-channel power mosfets. TO247. 75V. 4.5m?. VGS min2v max4v.
- 10x 1000v 50A bridge rectifiers.
- Several different toroid cores.
- 10x 2n2222 general bjt transistors.
- 1x 2600F 2.5V ultracapacitor.

*This is the only element of the induction heater inside the vacuum chamber, it will be electrically isolated by enamel paint + electrical tape.

I have been thinking about using this schematic:


I have very modest power requirements, as the vacuum will thermally isolate the melt. Only radiation out will be energy lost from the melt. I plan on melting copper, aluminium and some stainless steel. A power level between 1-2kW would be ideal.

Water cooling will be present, should I go with this very easy zvs schematic - modified for my own needs. Or should I go for a different topology? Suggestions, still KISS, will be highly appreciated

Last edited by storken; 01-25-2012 at 05:22 PM.
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Old 01-25-2012, 09:09 PM
BJT_user BJT_user is offline
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Circuit looks good and the MosFets you list will do the job. Though they'll need to be attached to very stout heatsinks to generate 1-2kw as you suggest. The 200mh choke will need to be changed to handle a LOT more than 10 amps of current. The list of parts you have doesn't show much that is usable besides the MOSFETs, copper tubing and the 1.8uf, 400 volt caps. You can use two of those caps in series to make a 0.9uf cap with a rating of 800 volts for the circuit. I don't see what power rating the 12v Zeners should be. Might want to err on the high side, like 1 watt or better.
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  #3  
Old 01-25-2012, 10:46 PM
storken storken is offline
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Quote:
Originally Posted by BJT_user View Post
Circuit looks good and the MosFets you list will do the job. Though they'll need to be attached to very stout heatsinks to generate 1-2kw as you suggest. The 200mh choke will need to be changed to handle a LOT more than 10 amps of current. The list of parts you have doesn't show much that is usable besides the MOSFETs, copper tubing and the 1.8uf, 400 volt caps. You can use two of those caps in series to make a 0.9uf cap with a rating of 800 volts for the circuit. I don't see what power rating the 12v Zeners should be. Might want to err on the high side, like 1 watt or better.
Well, nearly every component in that schematic must be changed or tweaked some.

Tried simulating in multisim, failed - didn't get the mandatory oscillations between the mosfets, even when sizing gate resistors differently I'll look more into it tomorrow.

Should I run 45uf total? with 1uH coil this gives 24kHz.
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Old 01-26-2012, 07:03 AM
storken storken is offline
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Tried many things in multisim today, can't get it to run. Uploaded the zipped .ms file here: if someone have free time, could you look at it?

Looking around for components at the moment. Will post up a list soon
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