2.5KVA transformer on square wave 1000hz mains

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I just bought a 50/60 hz transformer rated 575VAC pri to 230VAC sec
rated at 2.5KVA on ebay. I remember reading some time ago that
transformer companies rated their transformers to 1000 hz.

I'm needing like a 3KVDC at about 1.5KVA semi regulated supply but
don't like to use lots of mfd's of filtering at higher voltages to get
there. For a 4X1 PA ima building.

So I figure getting there by bridge switching 4 IGBT's at 1000hz
square wave on a 130VDC supply to the 230VAC winding on the
transformer. AT square wave I figure 325 VAC output, from the 575VAC
side.

Running a 10 step ladder multiplier I get 3250VDC. On a half wave
multiplier I figure the last step being hit by 100 hz pulses.

So Am I just spinning my Wheels and stick with 60hz and lots of mfd's
with a autoformer configuration getting more VDC per step and going
with 5 steps? And no easy way of regulation?

73
de N8ZU somewhere in 8 land

Re: 2.5KVA transformer on square wave 1000hz mains
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That voltage is very optimistic. Cockcroft walton ladders even at 3
stages give you nowhere near the Vout you'd expect, even on 1mA out. A
10 stager outputting 1.5kVA would be like building a 100ft tower out
of marshmallows.


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I don't see much point using a 2:1 transformer, it doesn't gain much.
Not everyone agrees, but imho once the voltage you're working with
gets evil, isolation from mains becomes of little value, if the V is
ground referenced. 3kV ref ground or neutral is little different.

The most practical way to get 1.5kVA is direct from a transformer, no
multiplier. And the most practical 1.5kVA transformer is going to be a
switcher, not 50/60Hz.

Regulation is most easily obtained by switching the transformer feed
on and off as the required Vout is reached.


NT

Re: 2.5KVA transformer on square wave 1000hz mains
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Sorry, but there I have to disagree. I personally built a three-stage
Cockroft-Walton that delivered a solid 2kW plus. It could deliver a lot
more but the plates in my tubes would have been glowing white instead of
read.

In the end what matters in a Cockroft-Walton cascade is the size of the
diodes and the size of the caps. I stepped up from 230VAC to 900VDC and
it held that rail like a rock. IIRC I put around a dozen 470uF caps in
there. That whole area had about the volume of half a shoe box.


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If you have the $$$, sure. The other way would nowadays be a switcher.
That makes the transformer really small but you have to roll your own
which isn't for the faint of heart. Plus EMC will be very critical
because it seems this is for a ham radio station.


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The utility isn't going to like that :-)

--
Regards, Joerg

http://www.analogconsultants.com /

Re: 2.5KVA transformer on square wave 1000hz mains

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IIRC tape wound toroidial transformers are often good to 1000Hz,

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microwave oven transformers?


--
⚂⚃ 100% natural

---

Re: 2.5KVA transformer on square wave 1000hz mains
"raypsi"  wrote in message20%

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Toroid transformers will easily handle 1000 Hz, and possibly as high as =
1520%
kHz, as I have demonstrated. When you go up in frequency, you can also =
go up20%
in voltage (and wattage) by a proportional amount. So you could use a20%
150-300 VA toroid transformer with a 24 VAC secondary and 240 VAC =
primary.20%
Create a 300 VDC bus from the 220 VAC line, and then drive MOSFETs or =
IGBTs20%
at 1 kHz into the secondary. The primary should be a 2200 VAC square =
wave20%
which you can easily rectify and filter to get the 2500 VDC you want. =
You20%
could also use a center tapped version and use a push-pull drive. I'm =
doing20%
that with a PIC16F684.

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The 1 kHz reduces the filtering requirements.

You might have problems with an ordinary line voltage rated toroid or =
other20%
type transformer when running at 3000V. The insulation might be rated at =
4kV20%
if it's a very good transformer, but that is just a surge breakdown =
rating20%
and not designed to be continuous. You may need to make the transformer20%
using high voltage wire. At 1 kHz you can probably get 5 volts/turn, so20%
you'd need several hundred turns (as is typical of small 220V power =
toroid20%
primaries).

A better idea might be a microwave oven transformer. Maybe two in =
parallel20%
if they are identical. Or two in series if you can use a +/-1500V =
supply.

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You might look at this website for high voltage stuff. But mostly they =
have20%
lower power sources like 10-50 mA. They do sell 5 kVA "pole Pigs" that =
are20%
14.4 kV, but they are about $700. However, surplus supply shops and eBay =

might have something.
http://www.amazing1.com/transformers.htm

Good luck, and be careful. I'm almost ready to finish my DC-DC converter =

which should provide 300-350 VDC at 5 amps from 12V, 24V, or 36V =
batteries.

Paul20%


P E Schoen has gone INSANE !!!

"P E Schoen"  has gone INSANE  !!!
-----------------------------------------

Toroid transformers will easily handle 1000 Hz, and possibly as high as 15
kHz, as I have demonstrated. When you go up in frequency, you can also go up
in voltage (and wattage) by a proportional amount.


** That  UTTER  NONSENSE was PROVED wrong here months ago  !!

While SOME increase in power throughput is possible, it is nothing like
proportional at 20 times.


So you could use a
150-300 VA toroid transformer with a 24 VAC secondary and 240 VAC primary.
Create a 300 VDC bus from the 220 VAC line, and then drive MOSFETs or IGBTs
at 1 kHz into the secondary.

**  COMPLETE  INSANITY.

  The insulation would  FAIL  in seconds  !!!!!


The primary
 should be a 2200 VAC square wave ...

**  Sppplaatttttt  !!!!!


The 1 kHz reduces the filtering requirements.

** There is virtually NO  filtering needed with a rectified square wave.


You might have problems with an ordinary line voltage rated toroid or other
type transformer when running at 3000V.


** No fooling  ................


The insulation might be rated at 4kV if it's a very good transformer,


** FFS  - WANKER  !!!!

Even if that figure is quoted - it is for 1 minute and from primary
to secondary  ONLY  !!!!
-------------------------------------------


but that is just a surge breakdown rating
and not designed to be continuous. You may need to make the transformer
using high voltage wire.

**  REALLY  !!!

Hundreds of turns of test instrument lead  ????


A  better idea might be a microwave oven transformer. Maybe two in parallel
if they are identical.


** Call the guys in white suits with the straitjackets  -   NOW  !!

( rest of this puke's drivel snipped  - cos it was making me too nauseas )



.....    Phil





Re: P E Schoen has gone INSANE !!!

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And good afternoon to you, too!

Jamie



Re: 2.5KVA transformer on square wave 1000hz mains
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Even normal EI core transformers of good quality do. I have one from the
60's here that I use to test aerospace designs at 400Hz. 15kHz is a
stretch though even for a toroid. Must be a really expensive one :-)


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Careful with that "proportional amount". There comes a point where the
insulation parameters aren't good enough anymore and ... tzzzzt ... *POOF*


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Insulation can also age with prolonged exposure to voltages at the
design limit.


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Except they aren't rated continuous duty like Ray most likely needs.
They are often only rated to get a bowl of top ramen to cooking
temperature :-)

[...]

--
Regards, Joerg

http://www.analogconsultants.com /

Re: 2.5KVA transformer on square wave 1000hz mains
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   Driving the 230V winding at 1KHz will allow a much higher voltage;
maybe 600V or so; output will still be about 2.5 times higher.
Autoformer mode would give 3.5 times.

   Naturally, lower value capacitors are needed for filtering on the
secondary at the higher frequency.

   Continuous (sine?) drive allows standard diode voltage multiplier scheme.
   Driving with a pulse gives something like a pulse at the output,
meaning you might try a 50V-200V supply and a FET to switch, like a
flyback, giving maybe 1-2KV peak primary and autoformer mode 3.5 times
that (roughly).
   Regulate by varying the primary amplitude.


Re: 2.5KVA transformer on square wave 1000hz mains
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You do not remember correctly.  Why would a transformer company rate
their transformers to 1000 hz?    There are a lot of trade offs in
transformer design.  It makes no sense to design a transformer to work
at both 60 hz and 1000 hz.  To work well it 1000 hz, you need to use
thinner laminations.  Designing for 60 only will let you make a
transformer that costs less and can be sold for less money.

This is not to say that one can not use a 60 hz transformer at higher
frequencies.  It will just not work as well as one designed for the
higher frequencies.

                                                              Dan

Re: 2.5KVA transformer on square wave 1000hz mains
On Sun, 22 Apr 2012 08:58:29 -0700 (PDT), " snipped-for-privacy@krl.org"

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In the tube audio power amplifier output transformer days, I did not
detect much differences between 50/60 Hz mains transformers and 30Hz -
15 kHz audio output transformers. Of course, you had to use sufficient
inductance for the low end performance and possibly do some layout
rearrangements for minimal stray capacitances for the high end
performance. A 7-8 octave bandwidth was not be something extreme.

The 50/1000 Hz frequency ratio is just slightly more than 4 octaves,
so I would not expect too much problems.


Re: 2.5KVA transformer on square wave 1000hz mains

< snipped-for-privacy@downunder.com
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** Irrelevant to the issue here - since audio output transforms are rated
for or the SAME input power across the band.

    NOT power that increases with frequency  ~!!



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** The problem is when you drive the primary with 20 times more voltage than
rated.

  The laminated core gets damn hot.

  The primary insulation, layer to layer and even turn to turn, breaks down.

  Capice ??


....   Phil




Re: 2.5KVA transformer on square wave 1000hz mains

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Nope, certainly not.  The laminations in any power transformer
will perform quite badly at much over a couple hundred Hz.
The thickness of the laminations needs to be reduced approximately
linearly with increasing frequency o keep iron losses down.
You can compensate to some extent by reducing Bmax, but that will
work against what you are trying to do.  What you would really want
is a custom ferrite core transformer.  You should be able to
buy surplus E-core or C-core pieces and possibly parallel a few
of them to get sufficent cross section.  At 1 KHz, a 2.5 KVA
transformer will not be very large at all.  But, then why stop
at 1 KHz, you can go to tens of KHz and make it even smaller.

Jon

Re: 2.5KVA transformer on square wave 1000hz mains
"Jon Elson"  wrote in message20%

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My experience has been more with toroids and variable transformers20%
(powerstats), which have thin tape wound laminations and are rated up to =
120%
kHz or even 2 kHz.
http://www.danaherspecialtyproducts.com/uploadedFiles/Siteroot/Superior_E =
lectric/Products_and_Solutions/POWERSTATAE%_Variable_Transformers/powerst=
at%20cat.pdf20%
(8MB)

I made a transformer from a powerstat and it worked up to 15 kHz, =
although I20%
didn't try to get much power from it. However, I will soon test it at =
about20%
1500 watts at 1 kHz, and it's original rating was about 500 VA at 50/60 =
Hz.20%
I also tried a regular E-I transformer from a 650 VA UPS, and it worked =
OK20%
at about 500 Hz. Again, I did not try to get much power from it.

For another project, I wound a small transformer on a split bobbin =
(COSMO20%
4143-1-20) and I tried both a ferrite core (Lodestone E75-52) and a =
powdered20%
iron core (Lodestone 9477016002), with a frequency of 57.6 kHz. The =
ferrite20%
core did not produce as much power and exhibited a lot of high frequency =

ringing, but the powdered iron showed a very good square wave and worked =

much better. This is just for about 2 watts for SCR gate drives, but I =
need20%
a very reliable high voltage isolation especially when used on 480V =
mains.20%
So even though I could have used higher frequency and a smaller package, =
the20%
voltage isolation and safe spacing made that risky, and I did not have20%
severe size limitations.

Same with the OP's application, but in his case he needs the windings to =

withstand 5kV continuous. So a larger transformer may be better so as to =

handle wire with thicker insulation and/or layers separated with thick20%
insulating tape. So I still think a tape wound toroid design may be20%
worthwhile. And for the amount of power and high voltage involved, it =
may be20%
safer to use a transformer designed for the purpose. I found some 4160V =
to20%
120/240V 1kVA to 5 kVA transformers on eBay for under $100, and they =
might20%
be ideal. Even a "potential transformer", normally used for metering20%
purposes, might be able to provide the needed power if run at a higher20%
frequency. At least the insulation ratings are designed for it.

Paul20%


Re: 2.5KVA transformer on square wave 1000hz mains
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We get transformers and inductors from an industrial transformer
manufacturer (they regularly use copper pipe windings), they use iron up to
about 1kHz, ferrite beyond.  You might hope a 100kVA transformer at 600Hz
has some amount of compactness to it, but you'd be wrong -- it's still about
the size of a cube fridge.  And that's running it near saturation (Bmax ~
1.5T, I think), so the cooling pipes run through the core as well.

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Yuck.  Powdered iron has no redeeming value for transformers anywhere.  Its
inductivity is too low for good transformer action, and in applications
where low inductance is desirable (e.g., isolated flyback converter), the
losses are so high that you get more delta B from ferrite (though the
average B can be higher, saturation ~0.8T typically).

Most likely, the reason you saw less ringing is because the inductance was
lower and the core looks like a solid resistor, damping most anything.
Optimized drive does the same thing without the power loss.

Tim

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


Re: 2.5KVA transformer on square wave 1000hz mains

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It is also possible that there was a little gap in the ferrite E cores. =
When20%
I took it apart to replace it with the powdered iron I had used for the20%
other transformer, it seemed that there may have been a bit of =
insulating20%
tape pinched between the E core mating surfaces. I'm working on another20%
project now, but when I return to that one I can try the ferrite cores20%
again. I have both #26 and #52 material (which I used). Maybe the #26 is =

better?

I can't go much higher in frequency with my prototype design because I'm =

using a PIC18F2420 which does not have a PWM module. But when I redesign =
the20%
board I can use a PIC that has built-in PWM, or I could use a separate20%
device to drive the transformer. I'm using an L298 module (which is way20%
overkill, and I'm only using half). So maybe I'll try an IRS2453D which =
is a20%
self-oscillating full bridge driver that costs only about $1.35 and can20%
drive some small MOSFETs. I don't need regulation. I have a 12V supply =
and I20%
just want about 8-12 VDC on the secondary for the gate drive circuitry.

Thanks,

Paul20%


Re: 2.5KVA transformer on square wave 1000hz mains
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Yuck, eww!  #26 and 52 are powdered iron numbers, not ferrites.  Both are
"high permeability", which is only 75.  You really want >500 for a
transformer, and >10k for a good transformer (pulse transformers, CTs, small
signal isolation, etc.).

Common powdered iron toroids are yellow/white (#26), which is very lossy,
only good for low ripple smoothing chokes, or blue/green (#52), which is
about half the losses and same performance otherwise, which isn't really
saying much as it'll still cook off easily with much ripple.  These are
common on older motherboards, where the smaller cores can tolerate some
ripple at moderate frequencies, but even then they can get quite hot.

Typical numbers for ferrite include Fair-Rite #77 and #78, Ferroxcube 3C80,
3C90 and such, and Magnetics types R and P for power (mu ~ 2200), #43 for
high frequency (mu ~ 800, good up to ~MHz), 3F3 and 3F4 for high frequency
power (up to about 1MHz), etc.; 3E6 and such, Magnetics type W for high-mu,
etc.

Obviously, you only get the best effective permeability with minimum gap.
Line filter chokes actually go so far as to use not just toroids but also
rectangle and "digital figure 8" shapes, single piece no mating faces, for
absolute maximum permeability.  Such ferrites go up to 15k, even 20k
permeability: when it gets that high, it's a fragile thing, easily spoiled
by ambient bias fields and current imbalance, but when small signal levels
are all that matters (swallowing up a little RFI on the line), it does a
great job.

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Frequency isn't a big deal; I've done the same thing with a discrete
oscillator (what could be simpler than a two transistor multivibrator?), a
little current boost (more discrete switches..), and a common mode EMI
filter choke ran "sideways".  Such inductors have tons of leakage between
windings, but the price is right for the amount of isolation you get.
Independent of size, I've found most CM chokes are only good for a watt or
two: if you run at a higher frequency, you can supply more voltage, but the
higher frequency drops more voltage across the leakage inductance, making
the supply "squishier"; for some desired output stability (like 10%),
maximum load current goes down, as a result, power remains roughly constant.

I personally wouldn't use L298, because it's a slow bipolar device with lots
of voltage drop (about 2V total under typical load, IIRC).  Gate drive chips
are the best choice these days; same basic operation (it pulls up to the
supply, it pulls down to ground), some even have disable pins (tristating
the output), and many are available in multiple units per package (a quad
driver with disable is equivalent to a CMOS L298, sans ground return pins).

With such inductive loads (as the powdered iron cores), you might need
schottky clamp diodes on the outputs to use CMOS chips; all that magnetizing
current might otherwise induce latchup.  (Gate drivers rated for maybe 1A
output are probably good for 0.25A reverse current; design accordingly.)

Dual "complementary" packaged transistors are also handy.  Sometimes too
handy: I once made the mistake of doing this,
http://myweb.msoe.edu/williamstm/Images/EE409_PWM3.jpg
forgetting that discrete transistors don't have the same softness of
monolithic CMOS circuits!  Poor tantalum capacitor was probably sweating its
balls off, while the transistors pulled 10-20A peak currents out of it for
~50 nanoseconds each cycle.  (Solution: nix the cap, soften the supply rail
with series resistance and inductance.  Supply bypass is actually a BAD
thing sometimes, and it's important to see when!)

SO-8 MOSFETs and arrays of course come in many sizes, these just happened to
sink that much current under switching conditions.  Protip: SO-8s are more
common than DPAKs or other packages.  Bizarre when you'd rather have a
compact, heatsinkable SOT89 than a flimsy SO-8, but I guess that's just how
the market is.  I've gathered a lot of SO-8 dual FETs from hard drives,
probably what's "driving" the market, among others.

For many purposes, a plain 2N7002 + BSS84 pair wired as a dumb CMOS inverter
is equivalent to most smaller monolithic drivers (0.5-1A peak current), with
the advantage that they are discrete transistors and can be operated much
faster.

Anyway, as it's late and I'm rambling again, I'd suggest a flyback converter
instead.  Something with UC3843 perhaps, like so:
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/12-6_DC-DC_Converter.png
(UC3842 shown, because the supply is 18V; 3843 has a lower UVLO threshold,
allowing it to work on >8V supplies.)
The feedback winding can be local, in which case both output channels have
the same mediocre regulation; it can be placed on one output (via TL431 and
opto, in the common arrangement), in which case one output is perfectly
regulated and the other is mediocre.  (Note that, since flyback stores
energy, but it demands large ripple, gapped ferrite is preferred over
powdered iron in the transformer core.)

Or you can buy the whole thing in an e.g. RECOM isolated converter, albeit
for >$20/ea.



FYI, are you aware your message encoding is quoted-printable?  It makes it
very difficult to quote as I have to enter the ">" manually.  Also, the word
wrap is slightly off by my reckoning.  IIRC, traditional is ~76 characters,
yours might be set 77-78, which isn't bad, just looks funny after a few
layers of quoting.

Tim

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


Re: 2.5KVA transformer on square wave 1000hz mains

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Yes, actually I got the types reversed. What I have in the working unit =
is20%
Fair-Rite 9477016002, which is a type 77 ferrite. It was the powdered =
iron20%
core that was ringing and unable to work well. Thanks for the heads-up! =
This20%
was a project I had started last year, got the samples, and then put =
aside20%
for a couple months while I worked on something else. When I returned to =

this project I did not check the part numbers, and the packaging did not =

specify whether the cores were powdered iron or ferrite.

I just downloaded the Fair-Rite catalog, and that seems to be very =
helpful.20%
The powdered iron cores were from http://www.micrometals.com /.

[snip - but saved for future reference]

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The closest DC-DC converter I could find that might meet my needs was =
fro20%
Traco Power, but although it was rated for 4000 volt breakdown, it was =
not20%
rated for 480 VAC mains isolation.

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Yes, someone had noticed that previously, but I am using Windows Live =
Mail20%
for my newsreader, and although it is set to plain text, it uses the =
quoted20%
printable, and also it no longer performs the automatic word wrap and20%
quoting characters, so I also must add the ">" manually. I have used =
X-News,20%
but it's more convenient to use the same application as my default email =

client. Maybe I should get something better, especially if it will also20%
handle email as well as news.

I have no idea how difficult it may be to handle the quoted printable. =
My20%
posts look fine to me, of course, and they also seem OK when I have used =

X-news. I think there are add-ons for most newsreaders that handle it.

Thanks,

Paul20%


Re: 2.5KVA transformer on square wave 1000hz mains


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http://www.danaherspecialtyproducts.com/uploadedFiles/Siteroot/Superior_Electric/Products_and_Solutions/POWERSTAT ®_Variable_Transformers/powerstat%20cat.pdf
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Well, sure, if you keep the peak flux down, the dissipation will also be
reduced.  That kind of goes against the reason for raising the frequency,
but it does help reduce cap size.

Jon

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