magnetics question

Weight is almost linear with power, and inversely with frequency.

When I needed a 115V 400Hz for DO-160 aviation equipment development, I ordered a 100W amplifier set from Amplimo

Mains transformer (toroid 115/230V in), rectifier, capacitors, amplifier module, and an extra mains transformer (used in reverse) for the 115V output. Added a 400 Hz oscillator with a timer controlled gain control (4051 MUX with some resistors) to create the required brownout and dropout profiles. The customer was so amused they ordered some for their production and test line (until then, they used a gigantic motor + 400Hz dynamo in the basement to get 400 Hz).

Arie

I think so... for a given core, power scales linearly with frequency. A simple scribble with a 4-winding transformer suggests that.

Thanks

John

You have to be prepared for larger core losses due to the higher frequency if you use the same core material.

The higher frequency core materials are bulkier for the same power due to the smaller permeability.

I'd use a 400 Hz transformer.

Yes, which is exactly why switching PSU's are now the standard. The cost saving in iron (ferrite) and copper and capacitors, and all transport costs, far outweighs (pun intended) the cost of the semiconductors.

And why airplanes use 400 Hz - the tiny transformers I had designed in in the product were amusing, 8 times smaller than the usual 50 hz versions.

Arie

Which is why I used (Amplimo) toroids - they are good until several kHz.

Arie

On a sunny day (Wed, 06 Apr 2022 08:53:22 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in snipped-for-privacy@4ax.com:

When I wind some transformer I usulally look at the no load primary inductance so it is high eneough not to drain power, Then for that L and the given Core material I get number of turns Many of thsoe core sellers specify a core size for a given power. The load current, number of turns and wire diameter will give you weight of the coils. That weight is to be added to the core material for total 'mass' if that is what you mean.

Why not balanced with 2 transistors and a transformer 48 to 120 V ___________ T1 ______ ||( )||(

48 V +--- ||( 120 V ______)||( T2 ||(__________

Dunno how accurate it needs to be, replace the T1 T2 with thyristors, tune it with a big cap and make it self-oscillating? ___________ T1________________ ||( | )||( === 48 V +--- ||( 120 V _|______________)||( T2 ____ ||(__________ feedback ____) ||

Or use the almost all knowing google:

select 'images' for circuits.

Yes was storm here too

On a sunny day (Wed, 6 Apr 2022 18:24:49 +0200) it happened Arie de Muijnck snipped-for-privacy@ademu.com wrote in <t2kesh$3t5$ snipped-for-privacy@dont-email.me:

Yes, that is how I make 60 Hz here in 50 Hz land,

100 W audio amp 60 Hz from PC signal generator in 50 Hz mains transformer connected the other way around. Not very efficient, but nice sinewave and no harmonics. A simple raspberry followed by a low pass could drive that (raspi audio out is some PWM I think, sure has RF on it).

It's pretty easy to connect a $10-or-so I2S audio DAC board to a Pi, rather than using the on-board audio DAC. The ones I've been using (based on Ti/Burr-Brown PCM-series DAC chips) put out a pretty clean waveform - one can add a very simple low-pass to block noise up above a few hundred kHz if necessary.

I think you're living in the past. 60-400Hz magnetics are routinely shipped around the world for local cost reduction, making 'iron' transport costs irrelevent.

Only end-use weight and volume remain signifigant.

RL

Their regulation capability is far better than that of the more conventional PSUs.

But why 400 then? A typical scaling factor would be 10, so 500Hz should be expected. Instead, they have selected the odd value of 8. Backward compatibility with an arbitrarily selected frequency back in the medieval times?

Best regards, Piotr

Aircraft are moving away from the fixed 400Hz frequency to variable

360-800Hz.

"On the other hand, the innovation of power supply system in aircraft performance in the system of power supply: 360~800Hz large capacity variable frequency AC power system is using gradually instead of the constant frequency of 400Hz power supply on most of the aircraft[3,4]"

Interesting. Why not DC then? It is going to be consumed by a switcher of some sort anyway, be it a PSU or motor controller.

Best regards, Piotr

My Piper Malibu distributed power in DC. Various instruments either used DC as is, or changed it to 400Hz. I believe larger A/C generate 3-phase.

A possible reason for limiting the frequency may be skin effect. When you have to run power from the engines under the wings all over the plane, the losses could become serious.

does relays and switches used for ~400Hz AC need to be beefed up like for DC?

That's an interesting, and difficult, question. I'm assuming power transformer with unknown load on the secondary, there's current-transformer assumptions which are 'way different.

Firstly, you need the core not to saturate at rated input voltage and no load; that means the core material's B-H curve has to be considered to set core size. This is about the magnetic flux distribution in the area (cross-section) of its path.

Second, you need the primary and secondary wire resistances to be low enough for acceptable heat losses (usually, primary and secondary will have same loss, but that'll have steps at available gage sizes...) which means every core shape will have differing size according to the throat available for windings. Variacs will have different rules, because there's no separate primary and secondary wire gage, This affects the magnetic path length, not the area.

Third, you need the whole assembly to stay cool; we don't usually see heatsinks on transformers, but every pole pig IS certainly a kind of keep-it-cool problem, and for high frequency, core losses (and maybe even skin effect in conductors) will have to be considered even for small items.

With only the first item considered, cross sectional area is constant for peak current-turns at no load, so expect V /f proportional to area, thus weight roughly scale by f**(-1.5). It's a project that'll benefit from log-log and/or semilog graph paper.

can't it be more or less simplified to: if you take a suitable transformer and run it at 8 times the frequency you can also increase the voltage 8 times, and thus get 8 times the power

Probably to do with still using rotating converters and other synchronous things. 24000RPM is feasible in 1950s technology, but much more gets hard.

There are constant-frequency generators that always make 400 Hz. I don't know how they work.

360 (sometimes 250) to 800 Hz is "Wild power", what you can get from anywhere to stay alive. A ram air turbine is "the thing you never want to see used."

Yes, that's correct. I was thinking, though, of resizing the core which would shorten the wire length required, thus allow thinner wire with similar resistance; a redesign of the transformer for the higher frequency is different from using the same transformer. So, my scaling assumes a transformer reconfiguration in shape. It doesn't get into the correct way to do that wire re-dimensioning, because that includes dissipation of heat changing with size... and heat can be shed by conduction, or convection, with different power laws.