Induction Heater

What got done:

• Measured frequency of LC tank with oscilloscope 
  • Unloaded work coil oscillated at 95.2kHz with 2uF capacitance
  • With two more capacitors (2.64uF total) the LC tank resonated at 83kHz
  • 9 capacitors gave 77kHz and 10 produced 71.4kHz
  • Frequency dropped by a few kHz with a load on the work coil
• Calculated the inductance of the work coil to be 1.43uH (from capacitance-frequency measurements)
• Measured current draw of induction heater from 24VDC power supply
  • Unloaded: 4.5A for 110W without object in work coil
  • Loaded with small ferrous object: current jumps to 6.4A and rises to peak at 8.3A (200W) before slowly dropping as metal object heats up
• Began building MultiSim model of circuit using experimentally determined work coil inductance

Issues:

• Work coil still gets excessively warm while running for longer periods of time; may lose structural integrity.  We plan to solve this issue by running for short periods of time or adding fans.

Next steps:

• Continue MultiSim modeling to compare theoretical to experimental results
• Test other metals for their behavior in the work coil

Heating a large nut to cherry red heat using eight capacitors:

Oscilloscope measuring 2.64uF LC tank voltage (after a 10x voltage divider):

What got done:

• Soldered on the chokes and finished the capacitor board
• Formed the work coil and soldered it to the board
• Connected the power supply to a switch and connected it to the driver circuit
• Connected an LED to show when the circuit has power
• Did initial testing with iron, achieving roughly 1000  degrees Fahrenheit in a short period of time

Issues:

• A power supply wire pulled away from the copper clad board, meaning we had to move our circuit around a little and re-solder for sturdier connection
• Our work coil reaches very high temperatures, especially with object being heated.
• Capacitor bank gets hot with prolonged use

Next steps:

• Part-Sim theoretical testing
• Possible future testing with varied capacitance

                          Bottom of the circuit

      Top-down view of circuit

What got done:

• Soldered in fast diodes
• Disassembled premade choke assemblies to improve utility
• Bent and soldered in LC tank copper busbars (made from 14AWG solid copper wire), with connections available for work coil
• Soldered in 4 out of 6 initial capacitors for cap bank
• Sourced wire for work coil

Issues:

• Component side of board is crowded with crossed component leads; must monitor and inspect to avoid shorts
• Unconfirmed, but chokes may be wound with too thin of wire for the level of current they will be handling

Next steps:

• Solder on chokes and two more capacitors
• Form work coil and solder on
• Add power connectors
• Solder in power LED and its current-limiting resistor
• Test!

Current state of the board, with four capacitors soldered on capacitor bank:

What got done:

• Soldered in Zener diodes, power resistors, 10K resistors
• Connected MOSFETs to central negative rail
• Created heavily-soldered rail for each MOSFET connection to positive
• Added solder to board to buik up positive rail

Issues:

• Difficult to connect copper pads with solder on board to make a continuous rail; solved by laying piece of solid-core wire across pads to facilitate connection
• Extra length of resistor leads were used to bridge gaps between copper pads

Next steps:

• Solder on more components
• Form work coil
• Create bus for capacitor bank
• Make connectors for interchangeable work coil
• Add power connectors

Shown below, solder trace side of board and MOSFETs:

What got done:

• Checked power supply for outputting correct voltage unloaded and under 590 ohm power resistor load.
• Inventoried and checked over all parts in BOM.
• Planned out part locations on protoboard
• Soldered in MOSFETS as most important element in circuit

Issues:

• Small board size is good for part stability but bad for routing traces.  Need to be creative with arranging high-current traces

Next steps:

• Solder on more components
• Create high-current traces by adding solder to protoboard
• Create bus for capacitor bank
• Make connectors for interchangeable work coil