Re: Does an electromagnet lag its input?
- From: John Popelish <jpopelish@xxxxxxxx>
- Date: Tue, 26 Feb 2008 19:35:33 -0500
sid wrote:
If I'm sending a 60 Hz sine wave to an electromagnet (inductor), then
won't the current through the coil lag the input voltage by 90 deg?
So if the magnetic field depends basically on the current and the
number of turns, the pull of the magnet will lag the input voltage by
a quarter-cycle, won't it?
Because of my application, I'd like for the input wave, as seen on the
scope, to match the timing of the magnetic pull. Is there a way to
compensate for the lag, like with a capacitor or something? Sid
The magnets pull is more closely related to the current than the voltage, so if you can monitor the current (with a current transformer and burden resistor, perhaps) that would get you close to seeing a signal proportional to the force. The shift between current and force involves eddy currents circulating in the iron pole pieces. Those also contribute to the magnetic force, but they are not in phase with the coil current. You would need to add a linear Hall effect sensor to the electromagnet if you really want to see the field strength.
By the way, paralleling the coil with the right sized capacitor (the one that reduces the total current to a minimum) will bring the voltage almost in phase with the line current, but the coil current will still have the same phase shift with respect to that voltage. The line current will just be phase shifted with respect to the coil current by the addition of the capacitor current to the line.
--
Regards,
John Popelish
.
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