T
Tim Williams
- Jan 1, 1970
- 0
So what kind of filtering does an induction heater need?
Potentially salient points...
10kW (240V, 50A USA supply) ultimate goal
~20kHz resonance (may go as low as 5kHz in the future)
Currently, DC filtering is 44uF (2 x (10 x 2.2uF film), filtering +V/GND/-V)
after inverter, then electrolytics at FWB (2 x 8 x 470uF 200V). Measured HF
ripple of 4% at 50V supply, 15A peak output IIRC.
I'm supposing a chunky inductor of some uH (or mH!) suitable to put a few
ohms in the way of >2kHz, at enough current that it doesn't saturate due to
line current, which is ZERO, for a common mode choke... The wire at least
will have to be 6 or 8AWG.
And as a wider question, what is the *point* of a common mode choke? I can
see differential mode, which is how I'm drawing the current for pete's
sakes, but I don't particularly intend to be swinging around wildly in
space, leveraging my chassis' potential against--air? I mean, how does a
grounded box like a computer produce HF hash when the case isn't also
radiating in some obvious manner? I don't see how to calculate the
inductance for a common-mode choke, out of the blue. And yet I've seen them
in switchers with two- and three-wire cords.
Tim
Potentially salient points...
10kW (240V, 50A USA supply) ultimate goal
~20kHz resonance (may go as low as 5kHz in the future)
Currently, DC filtering is 44uF (2 x (10 x 2.2uF film), filtering +V/GND/-V)
after inverter, then electrolytics at FWB (2 x 8 x 470uF 200V). Measured HF
ripple of 4% at 50V supply, 15A peak output IIRC.
I'm supposing a chunky inductor of some uH (or mH!) suitable to put a few
ohms in the way of >2kHz, at enough current that it doesn't saturate due to
line current, which is ZERO, for a common mode choke... The wire at least
will have to be 6 or 8AWG.
And as a wider question, what is the *point* of a common mode choke? I can
see differential mode, which is how I'm drawing the current for pete's
sakes, but I don't particularly intend to be swinging around wildly in
space, leveraging my chassis' potential against--air? I mean, how does a
grounded box like a computer produce HF hash when the case isn't also
radiating in some obvious manner? I don't see how to calculate the
inductance for a common-mode choke, out of the blue. And yet I've seen them
in switchers with two- and three-wire cords.
Tim