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):