Build an induction heater and become a metalsmith

April 8, 2012 By Leave a Comment

If you’ve ever wanted to forge, cast, or smelt metal, this project is right up your alley. It’s a 30 kVA induction heater built by [bwang] over on Instructables. It gets hot enough to melt and forge steel, iron, and aluminum.

An induction heater operates by surrounding the object to be heated with a coil carrying high frequency AC current. Basically, the entire setup acts like a huge transformer with a shorted secondary. To get these currents into a workpiece, [bwang] used a TL494 PWM controller as an oscillator. The output of the TL494 is filtered and amplified a few times to generate a huge amount of AC current.

Larger versions of [bwang]’s induction heater are found in foundries and forges all across the land; even though this small version sucks down 50 A out of a dryer or stove outlet, induction heating is very efficient. We’re actually wondering why we don’t see many home blacksmiths using induction heating, so we’ll leave that for our readers to discuss in the comments.

[sessions] reminded us of this induction heater from a few years ago. A little smaller, but still usable.

Filed Under: hardware, misc hacks Tagged With: , , , , ,

Auto power circuit for an arcade machine

March 1, 2012 By Leave a Comment

Some of the pinball machines which [Jeri Ellsworth] has restored have ended up in the break room at her work. We’re sure her coworkers are thankful for this, but sometimes they forget to turn off the power to the machines, and letting them run constantly means more frequent servicing will be necessary. She set out to fix the situation by building a circuit that will automatically power the machines.

We think the solution adds some much needed functionality. Instead of hunting for the power switch, you can now power the machine up by hitting the left flipper, and it will automatically shut off after about five minutes of not having that flipper button pressed. For this she grabbed a 555 timer chip and built a circuit to control the relay switching the mains power.

She added a magnet and reed switch to the left flipper switch assembly to control her add-on circuit. It connects to the base of a PNP transistor which controls a resistor network and capacitor. This part of the circuit (seen to the left of the 555 in the schematic) allows the timer to be re-triggered. That is, every time you press the flipper the 555 will reset the timer. Don’t miss the demo she filmed after the break.

[Read more…]

Filed Under: classic hacks Tagged With: , , , ,