Does an electromagnet lag its input?

[sid]

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

 

[Chuck]

On Tue, 26 Feb 2008 12:46:47 -0800 (PST), sid <sylvestersn@yahoo.com>
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

What about a small resistor in series with the electromagnet? The
voltage across the resistor will be in phase with the current, and
thus the magnetic field. You need to be careful connecting the scope
to 120 volt ac, of course. You could use a small transformer for
isolation.

Chuck

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[John Popelish]

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

 

[John Larkin]

On Tue, 26 Feb 2008 12:46:47 -0800 (PST), sid <sylvestersn@yahoo.com>
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?

It will lag, but by somewhat less than 90 degrees. It depends on the L
and R values.

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?

The pull on a nonmagnetized object is according to the absolute velue
of the coil current, modified by various complicated magnetic effects.

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

A series cap can resonate out the inductance, and can potentially
swing the coil current from lag to zero to lead, depending. It can
also increase the current, maybe by a lot.

John