Ferrite toroids cores DIY
But here a doubt arises. How do you calculate core saturation? I understand that this by means of a proven industrial process, with exact proportions and determined purity in the raw material, can be estimated.
Has anyone made ferrite cores? how do you know when saturation occurs (heat is bad)? how often have you worked them?
In my country I do not have the possibility to buy transformers or ferrite cores, so I have to try to manufacture it myself.
I need to make some SMPS power supplies and I don't have the transformers.
Someone has some formula or way to make them? maybe it's better than how I'm doing it.
A detailed discussion of ferrite material properties and manufacturing process can be found in Snellings classical book Soft Ferrites, Properties and Applications. Available as reprint or at archive.org
I followed an internet article about homemade inductors. I cut up steel wool into slivers, then mixed them with silicone adhesive, then packed the slurry into a short length of soda straw. I wound it a couple hundred times with copper wire. I think it's about 200 uH from its behavior in circuits.
As for saturation current, I'm pretty sure it's very low. Compared to soft iron, steel has worse permeability / retentivity / coercivity. Watching the oscilloscope waveforms, I recall seeing current ramp up during the first part of the cycle, then a vertical drop just as the second half of the cycle begins the ramp down. I think the vertical drop indicates the inductor generates less Amperes than the amount that went into it. In other words, saturation loss.
I suppose saturation would improve if I started with a larger slurry of steel slivers, but I cannot be certain how far magnetic flux penetrates through my inductor. Perhaps it has to do with the length-vs-diameter of the soda straw. Or distribution of wire turns. Etc.