Re: power losses across inductive chokes

On Sun, 26 Jul 2009 17:49:29 -0700, Totally_Lost wrote:

On Jul 26, 6:04 pm, "Phil Allison" <phi...@xxxxxxxxxx> wrote:
** The heat loss in any *resistance* will be given by the formula I
squared R,  where I is the RMS value of the current.

The RMS current value may consist of a DC plus and an AC RMS component
- which if known separately are combined by taking the square root of
the sum of the squares of each value.

Ok, that is a better definition of how to compute the resistive losses
for the AC component, that is super imposed on the DC offset voltage/
current.

In the case of an inductor with a magnetic core, there are additional
heat losses in the core and the R value of the copper wire will
increase at high frequencies due to skin effect and of course increase
with temperature by 0.4% for each degree C rise.

In this particular case, the inductor is an air core with a lot of
turns, so there are no eddy current losses in an iron core. The ripple
frequency is between 600 to 3000 Hertz. Is skin effect really a problem
at these low frequencies?

The all up loss is by no means a trivial thing to compute in a real
situation.

So, I still do not have an answer to the problem originally posted.

I suppose I should have put it more correctly as, are the actual choke
heating losses I^2 * Z, where Z = sqrt (R^2 + Xl^2) across the inductor?
This is implied by the AC voltage drop across the inductor as the
frequency increases. Not that different than the forward conduction
voltage drop across a diode the results in V*I losses.

Thanks!

To find the average power loss, plot the voltage drop across the
component times the current through the component as a function of time
and average the result.

Resistance causes a component of the product of current and voltage drop
that goes as 1 + cos(2*pi*f*t); reactance causes a component that goes as
cos(2*pi*f*t).

So what you were told is true, the energy from reactance just gets stored
in the inductor for a while then returned to the circuit later, while the
energy from resistance gets burned up.

--
www.wescottdesign.com
.

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