This Instructable will walk you through the construction of a high-power (30kVA) heater, suitable for melting aluminum and steel. Note that to take full advantage of this design, you will need a 220V outlet, at least a 50A single-phase one and preferably a 50A or 60A 3-phase outlet.
- This project uses mains voltage. While well-behaved, 110/220 mains can seriously injure, maim, and/or kill you if used improperly.
- The voltage across the tank capacitor can potentially ring up to hundreds of volts. Don't let the 20:1 step-down ratio fool you!
- When scoping the circuit, beware of ground loops.
- The work piece, naturally, can get very hot. DO NOT TOUCH! Less obviously, do not rapidly quench the work piece with water, as this can lead to dangerous sputtering.
- This project uses power electronics. Under fault conditions, semiconductor devices used in this project may rapidly heat, vent, and/or release rapidly moving shrapnel. Shield appropriately.
Step 1: Bill of Materials
- 2 IGBT half-bridge modules. I used Powerex CM400DU-12F 400A 600V Dual IGBTs; anything of similar power handling and switching speed should work. These can be purchased as cheap surplus from Ebay.
- 4 MOSFETs or IGBTs for the gate drive. I used HGTG30N60B3D's, which are way overkill for the application. They need to be able to dissipate about 30W without burning up.
- 2 gate drive IC's, of at least 9A peak current capability. I use the UCC37322 from TI.
- 2 ferrite toroids. These are your gate drive transformers, and should be able to pass a reasonably clean square wave at 50 kHz. Magnetics, Inc. and TSC Ferrite International are good manufacturers, or you can salvage them from old CRTs or switching power supplies. The powered iron cores from ATX supplies rarely work.
- Large ferrite toroids for the toroidial coupling transfromer.
- 1 TL494 PWM IC.
- 1 at least 20 uF, at least 20V film or ceramic capacitor.
- Assorted resistors, capacitors, and potentiometers for the driver.
- 10' of 1/4" soft copper refrigeration tubing.
- A water block capable of accommodating the two IGBTs. A large heatsink may also work, but I haven't tried.
- 2 aluminum or copper bars, ~3/4"x8"
- 2 1/4" compression unions
- A 4-position rotary contactor, good for several tens of amps.
- A screw-terminal electrolytic capacitor of reasonable quality. I recommend at least a few hundred uF for 3-phase operation.
- A high-quality, low inductance snubber capacitor for the bridge. Ebay has cute brick-mount 20 uF blocks for $5.
- One or more high-quality polypropylene capacitors for the tank capacitor. More on this part later.
- An analog current meter good for several tens of amps.
- A 3-phase bridge rectifier (or single-phase if you are willing to settle for single-phase operation only).
- A suitable project case and associated hardware (3-phase breaker, cord, plug, etc).
- A water pump capable of a couple GPM
- Tubing appropriate for hooking up the water-cooling.
- A Variac for testing.