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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: boosting an AC choke with a capacitor ? posted by tonemaniac on July 2, 2007 at 09:29:11:
The Hammond choke is a parallel filter. If you put a capacitor in series with it and tune the combination to a 60 Hz resonance, you will create a dead short across the AC! Something may catch fire before the circuit breaker clears.
Series L-C combinations have zero impedance (except for parasitic resistances) at resonance.
Parallel L-C combinations have infinite impedance (except for parasitic effects) at resonance.
There is not much point in making a parallel-resonant filter with the Hammond choke, as the combination will look pretty much like a capacitor above resonance. The DC resistance is high enough that the choke is not good for removing DC from the AC line, so you will have wasted a choke.
I measured the frequency for maximum impedance of a 193H choke. It was 5 KHz. For an inductance of 5 henrys, the parasitic parallel capacitance necessary to give a resonant frequency of 5 KHz is only 202 pF, which is a reasonable amount for the size of the choke coil. I expect the larger chokes (193L, 193M) will have similar or greater amounts of parasitic capacitance.
Thus, these chokes look like capacitors from the treble on up, and have the advantage of being above their primary resonance at important AC noise frequencies. Standard capacitors have parasitic inductance and look like inductors above their primary resonances.
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Follow Ups
- Careful! - Al Sekela 11:02:54 07/02/07 (1)
- Oh My! - Russ57 11:58:00 07/02/07 (0)
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