I have been working on a circuit for diverting excess power from solar charged batteries to a domestic emersion heater. The circuit measures the battery voltage, when it starts to approch 28V it increases a pwm output on the Arduino this then goes through an opto isolator into an IGBT switching 240V DC. This is all working fine, I have a web page with images and a description here:http://www.tdpe.co.uk/projects/tdp_wiki/index.php?title=Load_Dump_Circuit
The problem with this circuit is that it makes the heater element wine, quite loud and I am a little worried that it may fatigue the coil in the element. So I am thinking of adding a filter circuit with an inductor, capacitor, and a free wheel diode.
I have very little experience selecting inductors, would anyone be able to advise what would be sensible?
The element is 3kw 240v, I am planning on switching upto about 50% duty cycle.