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Registered Member #610
Joined: Wed Mar 28 2007, 09:44PM
Location: Middletown, RI
Posts: 110
Nothing really that impressive... just shows that you can get results easily. Bolt and nuts got up to 450C. Frequency was 200kHz-ish. About 50 to 70 Watts.
Registered Member #610
Joined: Wed Mar 28 2007, 09:44PM
Location: Middletown, RI
Posts: 110
Around 30-40 seconds.
I now feel justified with asking questions on this forum because I finally made something that works. Now its time for me to learn!!!:
My heatsinks were too small and the FETs burned out. I knew this would happen and was simply curious. I'm wondering where most of the power (that made them heat up) came from?
Input to rails was 120VRMS (wall voltage), and current in was 0.5ARMS. So power in is about 60W.
RSdon of FETs is 0.5 Ohms... so even if all of the available current went into the load coil, then the power wasted by the fets can't be more then a few watts.
Is this still enough to heat those puny heatsinks into meltdown, or is something else going on (like shoot through)? Any ideas?
PS: As part of my learning curve, I wasted *ALOT* of time and money because of old capacitors. I recently acquired hundreds of various capacitors from the Navy. I failed to realize that they were thrown out for a reason, not to mention they were decades old. Many attemps to build power circuits failed due to large leakage / mis-markings / super-high ESR of this crap. Transformers, inductors, and resistors can last forever: but capacitors? Get new ones! Now I know.
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
What is probably contributing to the heating is the IRF740s Rds-ON. 0.5 ohms is a lot. With rectified wall voltage, some lower voltage FETs and a couple TVS diodes might reduce heating.
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Simple induction heater
