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Is inrush current limiter responsible for quieter power transformer?
Is inrush current limiter responsible for quieter power transformer?
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Old 21st May 2019, 02:53 PM   #51
Bonsai is offline Bonsai  Europe
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Old 21st May 2019, 02:54 PM   #52
scottjoplin is offline scottjoplin  Wales
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Old 22nd May 2019, 01:07 AM   #53
N101N is offline N101N
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bonsai,
you hit the nail on the head in post #49.
Core saturation, magnetization hysteresis (that is about velocity rather than flux density), poor construction. In any event, adding fixed resistors would be beneficial.

Last edited by N101N; 22nd May 2019 at 01:19 AM.
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Old 22nd May 2019, 10:49 AM   #54
Bonsai is offline Bonsai  Europe
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Yes. If you drop the mains input voltage, it definitely helps but of course you then have power losses in the resistor.
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Old 22nd May 2019, 12:17 PM   #55
Mark Johnson is offline Mark Johnson  United States
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Is inrush current limiter responsible for quieter power transformer?
I suppose US buyers of dual-voltage transformers with two primaries, have the option of cutting the magnetization in half (to get a big margin of safety against core saturation) through brute force: Don't connect the primaries in parallel. Connect the mains to one primary and don't use the other primary at all; just terminate it with something harmless like a 22K 1W resistor. You've reduced magnetization by 2X, which of course cuts the VA rating in half too. But the additional cost of a doubled-VA transformer is not huge; for example the delta is $21 when going from 200VA to 400VA.
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Old 22nd May 2019, 01:04 PM   #56
djoffe is offline djoffe  United States
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I may be thinking about this wrong, but I'm not sure your suggestion would help so much...It would increase the DCR, which moves in the direction of limiting peak currents. If a few ohms of Input current surge limiting stops the buzz, then this should also help...Maybe that's the effect you're pointing to...and in that case, I'd have to agree.

Still, the apparent inductance wouldn't change, since both primary windings are tightly coupled, so the magnetizing current (dominated by the inductance) really wouldn't change so much...

It might be a game of inches...where a few Ohms is enough....but I thought it worthwhile to split this particular hair...

comments invited....
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Old 22nd May 2019, 01:09 PM   #57
Bonsai is offline Bonsai  Europe
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The formula for flux density is

Bm = E/(4.44*f*N*A)

where


Bm = Max flux density in Tesla

E = RMS input voltage

F = Frequency in Hz

N = # of turns

A = is the core cross sectional area in metres^2

For a typical commercial mains transformer, the flux density is run at 1.8 Tesla.

So, if you increase the turns, the flux density goes down (but the copper losses go UP).

If you want real low flux density, you could wire the two 110 VAC primaries in series but specify the secondary voltage for double the voltage you actually require.

Disclaimer: I have NOT tried this.

Separately, you can see why commercial suppliers reduce the windings and run transformers at the max flux density - you minimize copper losses, amount of copper used and utilize fully the available area of the core. However, not too good for high quality audio of course.

Last edited by Bonsai; 22nd May 2019 at 01:16 PM.
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