Re: generic snubber
- From: "Paul E. Schoen" <pstech@xxxxxxxxx>
- Date: Fri, 9 Jun 2006 03:24:42 -0400
"Fritz Schlunder" <me@xxxxxxxxxxx> wrote in message
news:e6b2n1$pa0$1@xxxxxxxxxxxxxxxx
"Paul E. Schoen" <pstech@xxxxxxxxx> wrote in message
news:128gpbk82dn83d3@xxxxxxxxxxxxxxxxxxxxx
Another way to look at it: For your 1000 VA loads, assuming 120 VAC at 8about
amps, it could be a pure inductive load of 40 mH with a peak energy of
2.9
J at 12 amps. The 47 ohms in your example would limit the voltage to a
reasonable 564 volts peak. This corresponds to 6.8 kW, so with 2.9
Watt-Seconds it would dissipate within 428 uSec. The capacitance
corresponding to this TC is 9 uF. Based on stored energy, it would be
18 uF at 600 V. The current draw for 18 uF would be 145 mA and theresistor
would dissipate about 1 watt.
Assuming you are referring to 18uF in series with a 47 ohm resistance, at
120V 60Hz, you might want to repunch those numbers...
Right. About 814 mA and power of 31 watts. A 3.3 uF capacitor would draw
about 145 mA, and it also makes an effective snubber without excessive
power, although a 1 kV spike could be generated compared to 500 V for the
18 uF.
A higher value of resistance can be used to reduce the voltage spike on the
capacitor at the expense of a higher overall spike voltage on the load. 150
ohms with 3.3 uF limits the capacitor voltage to 600 volts, while the spike
reaches 1.5 kV. The resistor will dissipate about 3.5 watts.
This is a useful exercise, and simulation clearly shows ringing and DC
current offsets due to inductance.
Thanks,
Paul
.
- References:
- generic snubber
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- Re: generic snubber
- From: Paul E. Schoen
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