Need an inductance calculator

[carbonzit]

I'm looking for an inductance calculator program (ideally free, of course). I downloaded Coil Maestro, but I don't think it does what I want it to do.

I want to be able to determine inductance (roughly, at least) given coil parameters (wire size, coil size and core material). Coil Maestro doesn't seem to have parameters for core material and seems to assume air-core coils.

Thanks in advance for the helpful reply.

 

[ericgibbs]

hi cz.
Look here, you have assume the ferrite characteristics.
What you really need is a LCF meter, a number of members have made a 16F628A based verison.

Online Calculator .:. Amidon Toroid Calculator (Ferrite)

 

[crutschow]

A google search turned up this.

Will that work for you?

 

[carbonzit]

A google search turned up this.

Will that work for you?

Maybe.

Actually, it probably will, but I have no idea what the permeability of my core material is.

If it's ferrite of an unknown type, what's the ranger here? a ballpark figure would be better than none at all (this is for the sake of finding a starting point for a simulation, not trying to build a super-accurate filter or anything).

I have two cores, actually: one is a ferrite bobbin that I cannibalized from a scanner control board (part of the motor driver circuit). The other is a little piece of ferrite I got by hitting a flat ferrite loop, the kind used to go around ribbon cables, with a hammer and cold chisel and eventually machining a piece just big enough to wind a little flyback transformer on.

 

[carbonzit]

hi cz.
Look here, you have assume the ferrite characteristics.
What you really need is a LCF meter, a number of members have made a 16F628A based verison.

Online Calculator .:. Amidon Toroid Calculator (Ferrite)

While a LCF meter would be a nice thing to have, at this point I'm just looking to ballpark inductances of transformer windings for a simulation.

Not sure that calculator you posted a link to will work. It's for toroids: will it work for non-toroids?

And while they give a drop-down list of core materials, I still have no idea what material my cores are. Plus their core sizes are also given as a list of (industry standard?) sizes (FT-27, FT-33, etc.). Do you know where I can find a reference to these sizes?

 

[crutschow]

The other is a little piece of ferrite I got by hitting a flat ferrite loop, the kind used to go around ribbon cables, with a hammer and cold chisel and eventually machining a piece just big enough to wind a little flyback transformer on.

If you use just a piece of ferrite and it doesn't form a magnetic loop then the inductance will be a lot less then if it forms such a loop. That is because the flux has to leave one end of the core, go into the air, and then loop around to the other end of the core. Thus the inductance will be somewhere between a closed-loop core and an air core. The inductance value of an open core is thus rather difficult to calculate for this reason.

 

[Brevor]

And while they give a drop-down list of core materials, I still have no idea what material my cores are. Plus their core sizes are also given as a list of (industry standard?) sizes (FT-27, FT-33, etc.). Do you know where I can find a reference to these sizes?

The FT numbers are Amidon part numbers, you should be able to find the specs on Amidon's web page.

 

[MrAl]

Hi,


Just a few notes on the construction which also depends on the intended end application.

For example, you have to be a little careful with home wound coils if they are to work with any dc current flowing though them because the dc current is capable of changing the inductance by a huge amount, sometimes as low as 1000 times lower than calculated without considering the dc current. With no air gap the core saturates quite easily and it's not easy to add an air gap in a toroid core that doesnt already have one. If it's a pot core then no problem though.
The wire diameter affects the coil too for RF applications.

You can measure the permeability of a core but the success of a procedure to do this depends on what kind of test equipment you own or can get your hands on at least temporarily. You might tell us what test equipment you have or can get.

 

[DerStrom8]

Hi, Carbonzit.
A while ago a friend of mine showed me this. It might be what you are looking for.
I hope this helps!
Der Strom

P.S. It's a download, but it has inductance, capacitance, 555 circuits, etc. It may be worth it

EDIT: Just looked at it again, myself, and realized the "inductance" part is only for the color codes. Sorry for the mistake.

 

[dougy83]

While a LCF meter would be a nice thing to have, at this point I'm just looking to ballpark inductances of transformer windings for a simulation.

If you have a DSO, you can get some rough inductance values by connecting the DSO, the inductor and a known value capacitor in parallel, then applying an impulse of a couple of volts to it to get it to ring - measure the period/frequency and get the inductance from: f = 1/(2*pi*sqrt(LC)) or L = 1/(C*(2*pi*f)^2)

Once you know the inductance for a given number of turns, you can use L = AL * N^2, where L is the inductance, AL is some constant specific to your given core & N is the number of turns to work out the inductance for other numbers of turns on the same core.

 

[JimB]

I have no idea what the permeability of my core material is.

Well, there's your problem!

Not all ferrites are created equal, there is a huge range of permeabilities, even more if you allow for the fact that the ferrite may actually be an iron powder.

Some ferrites work ok at high frequencies, some can only manage low frequencies.
Unless you make a lot of measurements, an unknown ferrite is just hard black shiny stuff.

JimB

 

[MrAl]

Hi again,

Yeah i was suggesting some measurements but i need to know what kind of test equipment he has.

 

[carbonzit]

All I have is a few multimeters. Not likely to get anything approaching "real" test equipment any time soon.

So it turns out I actually need (according to the LTspice simulation of another circuit) a transformer with 5 and 15mH windings. Can anyone give me at least a clue as to how I can construct this?

What I have to work with is a motley assortment of small ferrite bobbins. I believe by their size that they may have started life as 10mH inductors. I also have a couple small ferrite beads. Any chance I can get something close to the inductances I need with these materials?