Can self induction increase power consumption?

Thread Starter

Jucimar Carpe

Joined Mar 18, 2018
Hi folks,

My question relays on the difference of consumption power of a coil when it's on AC and CC regime.

A coil is made of copper wire with an air core, aplied on it a CC current of 1 amp, a measure was taken and nottice a 5W of power consumption. Then the power supply is changed to and AC power supply, now the consumption was about 5,5W. Now the coil was dismade and it is just a simple wire ( straigh line) and remais on AC power supply. Now the consumption is around 5W again.

I have some tought about it but i'm not quite sure. It seems to me that when you a CC regime on a wire, the coil only represent a indcutor it self and after a long time it turn just to be a short circuit, so this cant increase the power.
When i have the coil on AC regime, it creates a self induction made by a opsition to the real currente that pass trough the wire, in that, we need to increase the voltage of the power supply to still with 1 amp (effective).

Can someone help me to understand why this occurs?


Joined Sep 22, 2013
Steady current only encounters resistance, changing current has resistance PLUS reactance.

Resistance is always there.....reactance only appears when current is changing.

Resistance limits all current all the time.......reactance only resist/limits a CHANGE in current.

What makes it that there is two kinds of reactance. This is because we have two kinds of current changes in current. A fast change and a slow change.

A coil....(inductance).....opposes a fast change in current more than a slow change.

So as the RATE of current change increases......a coil has more reactance.

A capacitor (capacitance) works the opposite way. So as the RATE of current change increases.....a capacitor has less reactance.

When we add resistance and reactance is called impedance. And to be able to add resistance and reactance together.........we have to use what is called a math cross product.

You're gona love that.


Joined Sep 22, 2013
When we measure power dissipation in a resistor.......we measure the voltage across it and the current thru it. With a resistive load.......the peak current is in time or sync with the peak voltage.

So the current will follow the AC voltage in time or in phase. The maximum current will occur at the maximum voltage.

But a coil, or inductance.....will knock the peak current out of sync with the peak voltage. So we don't get the peak current until 90 degrees after the peak voltage....or a quarter cycle.

SO....Now......the peak current is not at the same time as peak voltage. If you measure the voltage and current of inductor...that power measurement is called apparent power.

That apparent power will measure higher than the real power of the coil. That power difference, between the apparent and true(real) stored in the magnetic field of the coil.