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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: Hammond 193L choke tweak for AC posted by wheezer on July 2, 2007 at 10:08:29:
'dI/dt' is the derivative of the current as a function of time. The more rapid the change in current, the larger this number will be.
If the change in current is instantaneous, the voltage is infinite. This is why switches arc when interrupting current to inductive loads, such as motors. In practice, the voltage developed depends on when during the AC current waveform the switch is thrown: if thrown when the current is zero, there will be no voltage. Since the current waveform follows the AC voltage waveform at 60 Hz, it is a matter of chance as to whether you throw the switch at a null, a maximum, or somewhere in between. Some toggle switches are rated for how big of a motor you can switch with them: they are built to endure repeated arcing at a certain level. However, you may not want to have the noise pulses in the power circuit to your video gear for your tests.
If you want to do rapid switching of the inductor in and out of the AC circuit, wire a snubber across the switch. The snubber will absorb the inductor energy and limit the voltage spike to a reasonable level. Typical values would be 0.47 microfarads at 600 volts and 100 ohms in series. This circuit will be invisible when the inductor is in the circuit (switch closed), but allow some inductor participation when the switch is open. You can use another switch in series to completely remove the inductor, as long as you remember to throw it first to switch the inductor into the circuit, and last to switch the inductor out.
The worst thing you can do is to repeatedly plug and unplug the inductor in a fancy outlet with the power on. The repeated arcing will damage the outlet contacts.
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Follow Ups
- V = L (dI/dt) - Al Sekela 10:36:17 07/02/07 (10)
- RE: V = L (dI/dt) - wheezer 11:12:13 07/02/07 (9)
- Agree, a 3KV or higher cap would be better. - Al Sekela 10:50:07 07/03/07 (8)
- RE: Agree, a 3KV or higher cap would be better. - wheezer 11:08:01 07/03/07 (7)
- Transformers offer some filtering, but not as much as chokes. - Al Sekela 14:22:41 07/03/07 (6)
- Dear Al : Why it is better to use transformers with lower turns ratios ? - diyaudiophile 01:24:14 07/10/07 (0)
- RE: Transformers offer some filtering, but not as much as chokes. - wheezer 20:52:21 07/03/07 (4)
- Experiment with all your power circuits. - Al Sekela 12:32:24 07/04/07 (0)
- RE: Transformers offer some filtering, but not as much as chokes. - bartc 06:38:50 07/04/07 (2)
- RE: Transformers offer some filtering, but not as much as chokes. - wheezer 07:00:01 07/04/07 (1)
- RE: Transformers offer some filtering, but not as much as chokes. - bartc 06:24:20 07/05/07 (0)
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