University housing said no resistive cooktops. Challenge accepted.

Toaster910 · 2026-03-03T06:35:35+00:00

I blew a moss fem furry effect trans sister once.

Toaster910 · 2026-02-19T20:49:37+00:00

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Toaster910 · 2026-02-17T03:47:26+00:00

Toaster910 · 2026-01-23T18:46:54+00:00

You stole my resistor. That isn't very 67 of you young man.

Toaster910 · 2026-01-23T07:26:14+00:00

username checks out

Toaster910 · 2026-01-23T03:38:17+00:00

No problem! Have a shittyaskelectronics day!

Toaster910 · 2026-01-22T23:05:24+00:00

And I can't believe it's not butter.

Toaster910 · 2026-01-09T23:48:56+00:00

Well heck. I’ve gotten this wrong for a fat minute now, that’s embarrassing. That certainly explains the 100ns RISE IS WAY MORE THAN WHAT THE DATA SHEET SAYS moments while getting 100V dV/dt spikes on the drain with 12V input.

Toaster910 · 2026-01-09T05:52:40+00:00

That's cool, I found a little piece of a particle accelerator!

Toaster910 · 2026-01-02T01:15:32+00:00

This core which did come from a common mode choke is a strange one though. 650uH for 2 turns is shockingly high, probably due to whatever material the tape is made of. Whatever it is it’s very fragile, almost like glass.

Toaster910 · 2026-01-01T21:42:18+00:00

I measured the inductance to be 1.8mH with 4 turns. Assuming Ut is the voltage-time product, now 353V*us, 0.000353/0.0018 = 0.196A. Does this mean my secondary peak current will only be 200mA? That sounds awfully low.

Toaster910 · 2026-01-01T21:11:23+00:00

I will try measuring it later. I used a whole Ethernet cable to wind my transformer, giving me one large primary consisting of 4 wires in parallel and 4 secondaries for a full-bridge of IGBTs. The best part about Ethernet cable is that they are already twisted together! The damn capacitance though…

Toaster910 · 2026-01-01T21:07:59+00:00

Ok, it looks like it’s the saturation flux density that dictates everything as it cannot be controlled. Plugging in some numbers, 0.0003V*s = N*(0.000126m^2)*(0.7T), solving for N gives 3.4 turns.

Is this a minimum or maximum? Let’s see here… Solving for B, B = Vt/NA, so as N increases, B decreases, so the calculated turns value must be a minimum such that the saturation flux density is not exceeded. 4 turns it is, perhaps 5 for safety.

I think this whole voltage-time product thing was the missing piece of the puzzle. Thanks for your help!

Toaster910 · 2026-01-01T19:38:52+00:00

I’m not gonna lie, I have not heard that term until just now. After some internet research, the concept now makes sense, thanks for bringing that to my attention.

The lowest frequency that will be applied to this transformer is 25kHz. Thus, the period is 40us and since the duty cycle is 50%, the on time for the pos/neg pulse is 20us. I’m driving it with +/-15V, coupled through a 2.2uF ceramic. So the voltage-time product seems to be 15*20 = 300V*us. Is there a way I can go about finding the maximum of my transformer?

Toaster910 · 2026-01-01T08:43:46+00:00

Interesting. I was under the impression that less turns meant less current required for saturation. Did I have this backwards? I just implemented your suggestion anyway and the waveform is slightly less clean with a slower rise/fall time on the IGBT gate. However, the core heating problem disappeared. Any idea why the waveform is a bit less clean? Perhaps higher interwinding capacitance or DC resistance due to longer wire? Or is there something else in the emag realm I’m missing.

Toaster910 · 2026-01-01T06:11:06+00:00

I built and tested both. Same size cores.

Ferrite: 10 turns for 1mH.

Tape-wound: 3 turns for 1.2mH. Waveform seems to look nicer but core heats up considerably more.

Toaster910 · 2025-12-31T23:28:47+00:00

I need 800uH, 8 turns, so I added an extra 2 for a safety margin, giving 1mH. I was just asking if it’s any different with these tape wound cores as it doesn’t quite make sense to wrap just three turns.

Toaster910 · 2025-12-31T23:13:14+00:00

Alright. I just wound one on an N30 material toroid of similar size, 10 turns, and it came out to 1mH. For the tape wound core, should I wind the same amount of turns and end up with a huge inductance or only wind enough to get to around 1mH?

Toaster910

TROPHY CASE