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?
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.
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.
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.
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.
Toroid transformers will easily handle 1000 Hz, and possibly as high as =
15=20 kHz, as I have demonstrated. When you go up in frequency, you can also = go up=20 in voltage (and wattage) by a proportional amount. So you could use a=20
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 = IGBTs=20 at 1 kHz into the secondary. The primary should be a 2200 VAC square = wave=20 which you can easily rectify and filter to get the 2500 VDC you want. = You=20 could also use a center tapped version and use a push-pull drive. I'm = doing=20 that with a PIC16F684.
The 1 kHz reduces the filtering requirements.
You might have problems with an ordinary line voltage rated toroid or = other=20 type transformer when running at 3000V. The insulation might be rated at =
4kV=20 if it's a very good transformer, but that is just a surge breakdown = rating=20 and not designed to be continuous. You may need to make the transformer=20 using high voltage wire. At 1 kHz you can probably get 5 volts/turn, so=20 you'd need several hundred turns (as is typical of small 220V power = toroid=20 primaries).
A better idea might be a microwave oven transformer. Maybe two in = parallel=20 if they are identical. Or two in series if you can use a +/-1500V = supply.
You might look at this website for high voltage stuff. But mostly they = have=20 lower power sources like 10-50 mA. They do sell 5 kVA "pole Pigs" that = are=20
14.4 kV, but they are about $700. However, surplus supply shops and eBay =
might have something.
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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.
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.
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 )
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.
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.
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.
My experience has been more with toroids and variable transformers=20 (powerstats), which have thin tape wound laminations and are rated up to =
1=20 kHz or even 2 kHz.
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at%20cat.pdf=20 (8MB)
I made a transformer from a powerstat and it worked up to 15 kHz, = although I=20 didn't try to get much power from it. However, I will soon test it at = about=20
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 = OK=20 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 = (COSMO=20
4143-1-20) and I tried both a ferrite core (Lodestone E75-52) and a = powdered=20 iron core (Lodestone 9477016002), with a frequency of 57.6 kHz. The = ferrite=20 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 = need=20 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, = the=20 voltage isolation and safe spacing made that risky, and I did not have=20 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 thick=20 insulating tape. So I still think a tape wound toroid design may be=20 worthwhile. And for the amount of power and high voltage involved, it = may be=20 safer to use a transformer designed for the purpose. I found some 4160V = to=20
120/240V 1kVA to 5 kVA transformers on eBay for under $100, and they = might=20 be ideal. Even a "potential transformer", normally used for metering=20 purposes, might be able to provide the needed power if run at a higher=20 frequency. At least the insulation ratings are designed for it.
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.
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
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.
It is also possible that there was a little gap in the ferrite E cores. = When=20 I took it apart to replace it with the powdered iron I had used for the=20 other transformer, it seemed that there may have been a bit of = insulating=20 tape pinched between the E core mating surfaces. I'm working on another=20 project now, but when I return to that one I can try the ferrite cores=20 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 = the=20 board I can use a PIC that has built-in PWM, or I could use a separate=20 device to drive the transformer. I'm using an L298 module (which is way=20 overkill, and I'm only using half). So maybe I'll try an IRS2453D which = is a=20 self-oscillating full bridge driver that costs only about $1.35 and can=20 drive some small MOSFETs. I don't need regulation. I have a 12V supply = and I=20 just want about 8-12 VDC on the secondary for the gate drive circuitry.
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.
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,
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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:
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(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
Yes, actually I got the types reversed. What I have in the working unit = is=20 Fair-Rite 9477016002, which is a type 77 ferrite. It was the powdered = iron=20 core that was ringing and unable to work well. Thanks for the heads-up! = This=20 was a project I had started last year, got the samples, and then put = aside=20 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
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[snip - but saved for future reference]
The closest DC-DC converter I could find that might meet my needs was = fro=20 Traco Power, but although it was rated for 4000 volt breakdown, it was = not=20 rated for 480 VAC mains isolation.
traditional
Yes, someone had noticed that previously, but I am using Windows Live = Mail=20 for my newsreader, and although it is set to plain text, it uses the = quoted=20 printable, and also it no longer performs the automatic word wrap and=20 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 also=20 handle email as well as news.
I have no idea how difficult it may be to handle the quoted printable. = My=20 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.
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