Hi Guys and Gals! Ok so this is my first post on this site so bare with me here.
I'm trying to figure out how strong some of the electromagnets I've built are, and so far I can only get to the number of At, Gilberts, and Oersteds. What I want to figure out is the Gauss and or Webers. Now it's my understanding if you have an air core coil, 1 Gilbert or 1 Oersted ( H ) are equal to 1 Gauss ( B ). But if you use a ferromagnetic core, the intensity ( B ) is magnified based on the size and permeability of the core. Here is where I get stumped, how do you solve for B? I've been plugging around the inter tubes for a while now and have found 6 different ways to solve for B. Can anyone give me a simple explainable formula for calculating Gauss in my electromagnets? Here are the specs of one of my magnets if that helps.
2.5" x .5" soft iron core
719' of 22 Awg magnet wire
At = 2328
Applied Voltage = 12
Ω = 11.6
Amps = 1.04
Thank you for any help!
Matt
Hi,
B is calculated from H by the simple formula:
B=ua*H
where
ua is the absolute permeability.
We are usually interested in the relative (incremental) permeabilty ur, which is:
dB=ur*dH
where
dB is the change in B and
dH is the change in H.
The trick is knowing what the permeability of a given core is.
To find this out, you have to consult the BH curve for the given
core, but often that's a little hard to understand too because
there is hysteresis. You can get an idea what the core is doing
however by looking at the BH curve so if you have that data
you are one step ahead.
If you dont have that data and you want to know something
about the permeability, you have to do some measurements
which arent that straightforward.
Energizing the core with a DC level with an AC riding on top of
it helps, because then you can calculate the inductance for
each level of DC you apply, then calculate the BH for that point
using a formula for inductance.
This test requires swinging the DC supply current from say 0 to
some maximum and doing the calculation for say 10 points
in between.
Just to show how unusual these measurements can turn out,
near 0.00A DC the core might show very low ur, then as the
DC rises the ur hits some maximum, then starts to fall again,
until the coil starts to look like an air core again with very
little ur.
Here's a formula for V knowing other things:
V = 4.44 BNAf x 10^(-8) {rms, and B in gauss, A in square cm, f in Hertz, N is number of turns, sine wave}
and this can be solved for B, so knowing H and knowing B you can
solve for ur with:
B=ur*H
at the various points.
Good luck.
Here's a pic of a typical BH curve...
**broken link removed**