winding my own inductors

[Simon]

I'm thinking of winding my own inductors, I don't need anything too specific so accuracy is not critical. how do I calculate roughly the resulting inductance ? bearing in mind with or without cores

[Zero999]

There are plenty of formulae on Wikipedia.
http://en.wikipedia.org/wiki/Inductor#Inductance_formula

What, inductance, frequency?

Laminated iron is good at very low frequencies <3kHz.

Various iron powered cores are good for 3kHz to 30MHz, different materials are optimised for specific bands.

Air core is better for very high frequencies, >30MHz.

[Simon]

its just a rough power filter (yea again - you know what for) I've given up trying to buy them

[Zero999]

As I said on the other forum, there shouldn't be any need for a filter, the inductance in the coil will smooth out any fluctuation in current, adding a chock will increase the losses and gain you nothing.

[Simon]

a low pass LC filter will help reduce spikes as spikes are like high frequency (high speed) and the output will react slowly to the fast rising spikes on the input.

please see attached EWB simulation, the spikes have been killed off by a mere 1mH coil and a 10 uF condenser

[Zero999]

Your circuit doesn't look like that through.

There's an inductor with a certain series resistance in parallel with the capacitor.

https://www.eevblog.com/forum/index.php?action=dlattach;topic=73.0;attach=51;image

The voltage across the inductor is not important here, the magnetic field is proportional to the current which carries on flowing through the free-wheeling diode in between pulses.

Car alternators have used PWM to regulate the field current without a filter for years and they work perfectly.

Here are some datasheets for car alternator regulator ICs, notice how all of them use a simple transistor driver and free-wheeling diode and none have any filtering to the field current?

http://www.irf.com/product-info/datasheets/data/irvr101.pdf
http://www.st.com/stonline/products/literature/od/1368.pdf
http://www.datasheetcatalog.org/datasheet/CherrySemiconductor/mXtuwrw.pdf

If you want to It depends on what you're doing if you just building a regulator, then I'd recommend ditching the whole idea and just use a regulator IC.

[Simon]

this is meant as a supressor, see how the very fast spike is easily killed off and made into a gentle sine wave of much less amplitude by the filrer, the diode shorts out the negative side of this and I'll be adding a zener and TVS after the filter to totaly cut out anything over 18 V, the odea of the above simulation is to show the effect of an LC low pass filter on a fast impulse.

The output will remain as PWM although I'll be adding a resistor in paralel with the control mosfet to keep some current flowing, this may be in the form of the original resistor in the regulator

[Zero999]

You really need to post the entire circuit - I can't help you much without it.