another inverter project

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Joined: 09/08/2007
Location: Australia
Posts: 3338
Posted: 12:13am 21 Jan 2020      

Nick, I found some of those ferrite U cores in my junk drawer. And a couple of them already had 22 turn windings on them !

So I fitted up one U core with 22 turns and another U core without any turns and measured 2.16mH with zero air gap.  My ferrite data book only has inductance figures for one U core and one I bar in combination of 6.2uH for one turn.

6.2uH x 22 x 22 = 3.0mH  Two U cores have a lot longer magnetic path than a U and an I, and will produce much less inductance, so 2.16mH is probably about right.

Anyhow, tried a 15mm gap and measured 110uH with just the one 22 turn winding plus one bare core.

My data book only has Hanna curves for 20mm square cores and 30mm square cores, not the 25mm square cores.  But even the much larger 30mm cores might be right on the limit to get to 120 amps at 50uH before saturation.

If I draw a line between the two curves and assume that might be something like a 25mm square core set, then I squared L of 250mJ with a 5mm gap might be about the limit which may end up at about 71 amps saturation for 50uH.

The data book is probably a bit conservative, but its going to saturate well before 120 amps even with a 15mm gap.

Only way to know for sure would be to build a choke testing rig.

Cheers, Tony.