Thoughts on running 50/60 Hz SMPS on 400 Hz

I don't have any experience at 400Hz, but I'd be wary of any SMPS that had power factor correction or automatic-voltage-switching built-in.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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That, and the y-caps in there might throw you a curve. Bottomline the manufacturer of the power supply would have to be asked.

Most likely they would not endorse use in an aircraft anyhow. Possibly it would also require an STC blessed by the FAA -> $$$.

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Use another domain or send PM.

"Dave"

** So your idea of a " normal " SMPS is what ??

One that has no PFC circuit ?

That could become a big problem if not designed for a frequency 8 times higher than usual.

Also, 400 Hz and its harmonics are far more likely to become injected into places you don't want them by induction and capacitive coupling than 50 Hz.

Maybe you can rig up a temporary 400Hz (at 230 volt ?) supply - using an audio power amp and a mains transformer (operating in reverse) to see what happens with your particular gear.

...... Phil

Dave wrote in news:4852ab62@212.67.96.135:

A method that works with many switchmode power supplies: Build a rectifier/filter box to insert between the 400 Hz mains and the switcher. In other words, supply the switcher with DC. This generally works even with switchers that include PFC. It doesn't require much capacitance to filter

400 Hz. Paul Mathews

"Paul Mathews"

** DC mains supply was abandoned about 100 years ago - for darn good reasons.

Even then it was only 240V DC not 350 V DC !!!

IMO - the fire safety hazards and risk of accidental misconnection of transformer loads are too great to even contemplate this option.

..... Phil

"Phil Allison" wrote in news: snipped-for-privacy@mid.individual.net:

Yes, there are several important safety considerations I didn't mention. I had the idea that the OP was wanting to temporarily power some gear aboard an aircraft, as opposed to providing some kind of product or fixed installation. Paul Mathews

You are correct. Also, the aircraft will not be flying.

** That is a total red-herring.

Even building one 230AC to 350 volt DC supply adaptor is very dangerous - since the only practical way to do it is to use domestic 230 volts AC connectors at the output.

The fire risk is way too high.

..... Phil

Dave wrote in news:485434f5@212.67.96.135:

If you can verify that the equipment is powered by switchmode converters, with no internal auxiliary supplies powered by linear transformers, the DC approach can work safely. (This is done all the time in home-built electric vehicles, where there's a DC high voltage bus available from the traction battery bank.) There are serious safety concerns, of course, not least because DC fuse protection is required, since fuses designed for AC won't necessarily interrupt a DC arc. Also, the bridge rectifier input in the equipment will have only 2 of its rectifiers conducting with DC input.That means a higher average current in those rectifiers, partly cancelled out by the fact that there is no crest factor involved when you supply DC, so the rectifiers generally don't run much hotter. In any case, there is usually a high voltage DC bus inside the equipment, just upstream of the switching regulator. If it were me involved, I'd build and test a special kind of power cord for each piece of equipment, with proper connectors, fusing on both the 400 Hz and DC sides, and connectors at each end. Phil definitely has a point about the safety risks. Paul Mathews

-- "Too much", actually. The transformer in my Tek 475 has quite thin laminations. It's rated for 50-400Hz, of course. Eddy current losses go up with frequency.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Tim Williams" "David Starr"

** But not for a given transformer and fixed primary voltage.

Raising the input frequency by a factor of 8 reduces the core magnetisation by a similar ratio - so core losses remain much the same or even reduce.

...... Phil

Eddy current losses are proportional to square of frequency and square of magnetic flux. (At frequencies low enough for this to not get complicated much by skin effect, stray inductances, whatever)

However, volts per turn is proportionate with magnetic flux and frequency. That means eddy current loss is proportional to square of volts per turn, unaffected by frequency.

Hysteresis losses are actually improved by using a higher frequency. Those are *roughly* proportionate with square of magnetic flux but only linear with frequency - so with constant volts per turn, this loss is roughly inverse proportional to frequency.

(Hysteresis losses have messy nonlinearities, and the above is an oversimplification.)

The usual problem with operating 50/60 Hz iron core transformers at 400 Hz is that leakage inductance in the transformer sometimes causes output voltage to be less (with load) at 400 Hz.

- Don Klipstein ( snipped-for-privacy@misty.com)

Hmm, I'll believe that, but then, if that's the case, why ARE the laminations thinner in my scope's transformer? Why use thin laminations at any frequency if it factors out?

Tim

-- Deep Friar: a very philosophical monk. Website:

"Tim Williams"

** Fuckwit TOP POSTER !!!!!

** Wanna think that last bit of drivel through again ??

..... Phil

Making laminations thinner is done to reduce eddy current loss. With that loss (and source of heat) being about the same at 50, 60 and 400 Hz, making the laminations thinner makes things better at all of these frequencies.

I suspect the laminations are thinner either as part of the transformer being a better one, or to counter increased core loss by using lower cost core material or skimping turns/volt. This is to make a cheap transformer less bad, or to make a good one better. Less heat from the transformer may be something sorely needed in something as compact as many modern oscilloscopes.

Someone I have worked with tells me that a pretty good quality core material with fairly reasonable (not bargain basement) cost is "29M6". That comes in laminations thinner than those in the usual fare from low bid contract manufacturers.

- Don Klipstein ( snipped-for-privacy@misty.com)