Was reading about buck converters and the amps that are to flow through it. Say you wanted to build a 15 amp buck, I have looked all over the internet for large inductors and only found little ones 1 to 3 amps, where are the big ones. I seen some 20 amp bucks on ebay, but the inductor looked like the 1 to 3 amp ones I see everywhere. So where are buck converters that deliver high current getting the big inductors. Thank you

 

The inductor physical size depends upon the inductance and the current.
How much inductance do you want?
The higher the operating frequency, the lower the inductance required for a given output current, which is why modern switching regulators operate at a high frequency.
For example, here's a few inductors rated from 15A to 20A.

 

There are plenty of off the shelf inductors suitable for tens of amperes, but inductances are generally low, making them suitable for converters with low volt-second product across the inductor (i.e. high frequency and/or low output voltage). Many of the nice ones, in terms of characteristics, are surface mount. If you need more than a few microhenries, the off-the-shelf choices become much more limited. Procuring suitable cores and wire and winding your own then likely becomes necessary. I have a preference for toroids because of their desirable self-shielding and good cooling properties, but they are harder to wind than other forms. There are companies that specialize in winding transformers and inductors if you need a custom part in volume.

Coilcraft offers a pretty good range of standard inductor products.
I've used lots of Micrometals cores and some from Magnetics, Inc. The latter's KoolMu is a nice improvement over powdered iron at a more affordable price than molybdenum permalloy powder (MPP), which is an excellent but very expensive core material.

 

LTspice

 

Good for the few kilowatt range are kinescope-type TV receiver or kinescope type PC monitor ferrite cores. Windings may create anyone even in kitchen on the knee. But those cores badly habit over some 20 kHz.
Better are India 1x1x4 inch parallelpiped-style ferrite cores, cost very small (about dollar per piece) but keeps 0,36 Teslas (!) and 100 kHz. They allow to glue togther practically any kind of S and Q thus the hundreds of kilowatts or even megawatt is no the stopper. The bad side that some 2 to 6 months are lead-in time.

 

Thanks all, always a good source of hard to get info.

 

https://www.amazon.com/SUPERNIGHT-Switching-Universal-Regulated-Transformer/dp/B01LATMSGS