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What are the steps to work out the coupling coefficient of this coil transformer as I would like to plug these values into a spice model and in this regard I need a "K" value for the transformers coupling coefficient....
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
You can calculate it very precisely from the geometry with the Inca program: You can also measure the inductance of the two coils connected in series, that shall result in L1+L2+2*M. With M, the mutual inductance, calculate k=M/sqrt(L1*L2).
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Calculating the coupling would need finite element analysis software but you can measure primary and secondary inductances and mutual inductance and from that you can calculate the coupling coeficient. k = Lmutual/sqrt(Lpri x Lsec)
If you don't have an inductance meter (most of us don't) then you can use resonance with a capacitor to calculate the inductances.
Registered Member #1571
Joined: Wed Jul 02 2008, 03:26AM
Location: Bendigo Victoria Australia
Posts: 44
Thanks guys for your direction,
I have a couple of questions relating to Inca...
1. What do the Segments/turn relate to?
2. It tells me that the wire for the secondary is to big... the coil is built and I used 0.5mm wire. I have used a height of 0.05 or 50mm and I pput 26 layers of 80 turns.. its telling me that I need to use a wire width of 0.00003 rather than 0.0005... what settings am I screwing up here...
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
For a set of two coupled coils L1 and L2, you could use the following formula:
k = (1 - L1*/L1**)^1/2
where L1* is the inductance measured at the terminals of coil L1 with coil L2 shorted, and L1** is the inductance measured at the terminals of coil L1 with coil L2 open. (Of course the designations L1 and L2 could be interchanged).
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
si2030 wrote ...
I have a couple of questions relating to Inca...
1. What do the Segments/turn relate to?
If the program has to do a numerical analysis to calculate something, it divides each turn of the coils in this number of discrete segments. Increase if you want absurd precision, but for most calculations this is not used.
2. It tells me that the wire for the secondary is to big... the coil is built and I used 0.5mm wire. I have used a height of 0.05 or 50mm and I pput 26 layers of 80 turns.. its telling me that I need to use a wire width of 0.00003 rather than 0.0005... what settings am I screwing up here...
The program only supports single-layer coils (something to update...). If the windings are thin you can cheat and just use the recommended thickness for an equivalent single-layer coil with the average radius. M will be calculated correctly.
3. what does the base elevation refer to?
Elevation of the base of the coil relative to the base of the reference. Click in "view" to see.
4. Finally what do Segs/turn for L refer to?
The same of the first question, but for inductances, that are more difficult to calculate precisely and require more segments.
Registered Member #1571
Joined: Wed Jul 02 2008, 03:26AM
Location: Bendigo Victoria Australia
Posts: 44
Hi Antonio,
I have one more question and it may be that I have screwed up but I am getting an odd result for the primary inductance when measured. The settings I used were 20 turns, a height of 0.05M or 50mm. a Min Radius of 0.185M or 185mm with the max Radius equal to 0.185M or 185mm. Base elevation of 0 and a wire diameter of 0.0021M or 2.1mm.
The program provides an inductance of 0.24 to 0.26mH.
However when I use my peak inductance tester I get 35 micro henries....
So is the inductance tester so wrong? it did measure the secondary at 2 Henries where the calculated value was around 2.1 Henries...
Why should it measure such a different value and which is right..
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
35 uH is surely too low for these dimensions. Verify if the coil looks as the drawing made by the program. If the dimensions are correct, the coil may have a short-circuit, or you measured the inductance with the coil over a metal plate, or with a metal core.
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How to work out the coupling coefficient of an air coil
