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Volts-per-turn vs Frequency, Inductance, and no load / full load current

I have a toroid core that I previously wound based on my idea for using =

600=20 Hz or 1kHz or so to get higher power. The core is about 1.6" deep and = 3.4"=20 diameter with a 2" diameter hole. This is probably the 80 VA core from=20
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kits.htm,=20 which is rated at 0.12V/turn. I wound it with about 100 turns of #18 AWG = as=20 a secondary, and two windings of 8 turns each of #10 AWG as a primary. = If=20 volts/turn is proportional to frequency, this should be 2 volts/turn at = 1000=20 Hz, so I should be able to apply 16 VAC to the primary in a push-pull=20 configuration, using a 12 volt supply. And I should be able to get 150 = VAC=20 out.

I measured the inductance of each primary coil as 180 uH, and the = secondary=20 is 3.2 mH. I did a simulation with a FWB rectifier and 680 uF filter=20 capacitor, and I got 19 to 27 amps in each MOSFET during the ON cycle, = and=20

1.57A at 157V into the 100 ohm load, for 246 watts. The input power is = 250=20 watts, for 98.6% efficiency (probably unrealistic). So far, so good.

Now I disconnect the secondary, and my input is 120 watts. This is 40 = watts=20 in each of the primary coils which I have designated as 10 uOhms = resistance.=20 The MOSFETs (IRF2903ZS) dissipate only 165 mW. The 12V source is = supplying=20

11 A RMS and it has a 2 mOhm resistance, so that's not where the extra = 40=20 watts is coming from. The current through the source varies between +20=20 and -8 amps on one cycle and 6.2 to -24A on the other.

My question is if this is a normal magnetizing current for such a=20 transformer. When I change the parameters to what the transformer = probably=20 would have at its original rating of 120 VAC, 60 Hz, with 0.12 V/turn, I = get=20

3.2 H, and the magnetization current is about 166 mA RMS. The expected=20 current at its 80 VA design is 80/120 or 667 mA, about 4 times the no = load=20 value.

And my modified transformer should be 1.33 kVA with a primary current of =

111=20 amps, which is ten times the magnetizing current.

Magnetic theory is not my strong point. Are these figures about right? = Is=20 this a reasonable design for a 1 kVA DC-DC converter? I like the fact = that=20 the MOSFETs run so cool. Size and weight are not a huge factor. The iron =

core toroid should be much more rugged than a ferrite design, and may be =

similar in cost, especially for small quantities. And the electronics = should=20 be very simple. A 500 watt DC-DC converter costs about $250, and two of = them=20 would be 2.4 x 1 x 4.6 inches, and weigh about 0.5 kG or 1 .1 pound. But = at=20 best it's 90% efficient so it would need to dissipate 100 watts of = power.=20 Mine would be about 10 times larger and heavier, but cost about 1/5 that = of=20 the Lambda converter:

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If and when I finish a practical design and build and test this beast, = there=20 are unknown factors that may come into play, such as losses at the = higher=20 frequency. But AFAIK toroids like this can be used up to 2 kHz. = According to=20 the following engineering bulletin=20

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Staco variable=20 transformers can be used up to 2000 Hz with little or no derating. But = of=20 course that does not imply a higher power output, so that may be = misleading=20 or not directly applicable. However, I have seen data elsewhere that = says=20 the usual (or somewhat thinner) nickel-steel laminations can be used at=20 least to 400 Hz and even over 1000 Hz.

Following is my LTSpice circuit:

Paul

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =

12V-160V.asc = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

Version 4 SHEET 1 880 680 WIRE 304 128 224 128 WIRE 320 128 304 128 WIRE 432 128 384 128 WIRE 496 128 432 128 WIRE 560 128 496 128 WIRE 592 128 560 128 WIRE 96 144 -160 144 WIRE 224 192 224 128 WIRE 320 208 272 208 WIRE 432 208 432 128 WIRE 432 208 384 208 WIRE 592 208 592 128 WIRE 496 224 496 128 WIRE -496 240 -576 240 WIRE 96 240 96 224 WIRE 96 240 -496 240 WIRE 96 256 96 240 WIRE 272 272 272 208 WIRE 272 272 224 272 WIRE 320 272 272 272 WIRE 416 272 384 272 WIRE -320 288 -384 288 WIRE -80 288 -256 288 WIRE -384 304 -384 288 WIRE -256 336 -256 288 WIRE 96 336 0 336 WIRE -496 368 -496 240 WIRE 304 368 304 128 WIRE 320 368 304 368 WIRE 416 368 416 272 WIRE 416 368 384 368 WIRE 496 368 496 288 WIRE 496 368 416 368 WIRE 592 368 592 288 WIRE 592 368 496 368 WIRE -160 384 -160 144 WIRE 0 384 0 336 WIRE -576 416 -576 240 WIRE 592 432 592 368 WIRE -320 464 -320 288 WIRE -208 464 -320 464 WIRE -80 464 -80 288 WIRE -48 464 -80 464 WIRE -576 528 -576 480 WIRE -496 528 -496 448 WIRE -496 528 -576 528 WIRE -384 528 -384 384 WIRE -384 528 -496 528 WIRE -256 528 -256 416 WIRE -256 528 -384 528 WIRE -160 528 -160 480 WIRE -160 528 -256 528 WIRE -80 528 -160 528 WIRE 0 528 0 480 WIRE 0 528 -80 528 WIRE -80 608 -80 528 FLAG -80 608 0 FLAG 592 432 0 FLAG 560 128 Vout SYMBOL ind2 80 128 R0 SYMATTR InstName L1 SYMATTR Value 180=B5 SYMATTR Type ind SYMATTR SpiceLine Rser=3D10u SYMBOL ind2 80 240 R0 SYMATTR InstName L2 SYMATTR Value 180=B5 SYMATTR Type ind SYMATTR SpiceLine Rser=3D10u SYMBOL ind2 240 176 M0 SYMATTR InstName L3 SYMATTR Value 32m SYMATTR Type ind SYMATTR SpiceLine Rser=3D200u SYMBOL nmos -208 384 R0 WINDOW 3 56 102 Left 2 SYMATTR InstName M1 SYMATTR Value IRF2903ZS SYMBOL nmos -48 384 R0 WINDOW 3 56 102 Left 2 SYMATTR InstName M2 SYMATTR Value IRF2903ZS SYMBOL voltage -496 352 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 132 Left 2 SYMATTR SpiceLine Rser=3D2m SYMATTR InstName V1 SYMATTR Value 12 SYMBOL diode 384 288 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value MUR460 SYMBOL diode 320 224 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value MUR460 SYMBOL polcap 480 224 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 560=B5 SYMATTR InstName C1 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D600 Irms=3D2.9 Rser=3D0.018 Lser=3D0 SYMBOL res 576 192 R0 SYMATTR InstName R1 SYMATTR Value 100 SYMBOL voltage -384 288 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -43 57 Left 2 WINDOW 3 -192 268 Left 2 SYMATTR SpiceLine Rser=3D50m SYMATTR Value PULSE(0 10 250u 10n 10n 495u 1000u 100) SYMATTR InstName V2 SYMBOL voltage -256 320 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -43 57 Left 2 WINDOW 3 -322 268 Left 2 SYMATTR SpiceLine Rser=3D50m SYMATTR Value PULSE(0 10 750.5u 10n 10n 495u 1000u 100) SYMATTR InstName V3 SYMBOL diode 320 144 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL diode 384 384 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D4 SYMATTR Value MUR460 SYMBOL polcap -592 416 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 2200=B5 SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D25 Irms=3D2.9 Rser=3D10m Lser=3D0 TEXT 72 384 Left 2 !K1 L1 L2 L3 1 TEXT -584 624 Left 2 !.tran 0 200m 0 1u startup TEXT 160 440 Left 2 ;Primary 2x8 turns 2V/turn at 1000 Hz TEXT 160 472 Left 2 ;25 A peak magnetizing current for 180u 1kHz TEXT 160 496 Left 2 ;27 A peak current at 100 ohm load=20

Reply to
P E Schoen
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I hope you mean 120VA! From your LTSpice example I get only a couple of watts at no load.

Cheers, John

Reply to
John S

Ok, so it has a 1.6 x 0.7" cross section, or 723 mm^2. At Bmax = 1.2T, that's 867uWb/t maximum flux.

8 turns gets you 6937uWb flux, which is 30.8V RMS sine at 1kHz. If you're driving it with a square wave, that becomes 27.7V peak. If you're driving it in push-pull, the total across 16 turns is 55.5V, etc.

The magnetic path length is roughly 215mm. At a typical average permeability of 10k, you'll have an inductivity of 42uH/t^2, or 2.7mH primary inductance.

Steel is very nonlinear, so you might expect the average value to be as high as four times that, and the initial value to be perhaps only a tenth -- that you measured 180uH suggests your initial permeability is around 670, which is reasonable.

When it comes to transformers, all you need to check are:

  1. If the average permeability is over 1000 or so, magnetizing current will simply be too small to care about. Don't even measure or calculate inductance, because as you can see, it varies like crazy. A transformer may bear superficial resemblance to an inductor, but it serves a very different purpose -- power conversion, not energy storage.
  2. Make sure that you have enough turns and core area, so that the flux density remains below saturation at the highest voltage and lowest frequency you'll be running at. This is calculated: N = Vrms / (4.44 * F * Bmax * Ae) where N is the number of turns, Vrms is the RMS sine wave voltage applied to those turns, F is frequency, Bmax is saturation flux density (usually 1.2T for steel), and Ae is the cross sectional area of the core.

You can calculate inductance as an exercise, but like I said, it's not representative of actual results: L = N^2 * mu_0 * mu * Ae / l_e where mu_0 is the permeability of free space (~= 0.001256 uH/mm), mu is the permeability of the core material, and l_e is the magnetic path length. Without the N^2, this is A_L, the inductivity of the core.

If an air gap is present (typical of E-I choke designs; obviously, difficult to arrange for stripwound toroids), the path length changes. Specifically, compared to air, the core has an equivalent path length of l_e / mu, which clearly becomes negligible when mu is thousands. So, for an air gap of just a few tenths of a milimeter, the airgap dominates the inductance, inductance drops, and energy storage goes up -- because the saturation flux remains approximately constant, while the inductance drops linearly (for small gaps), and current at saturation rises linearly. Energy goes as current squared, so energy rises linearly also, which makes sense because air is a good way to store magnetic energy.

If you wish to perform a simulation to determine what voltage and frequency you can run, you need a nonlinear core model. The simplest way is a voltage integrator feeding diodes, feeding back the diode current as terminal current. Because the diode voltage is phase shifted by the integration, a resistance in parallel with the diodes looks inductive at the terminals; a capacitor in parallel with the diodes looks resistive at the terminals. In this way, eddy currents can also be modeled.

If you just want to get the required parameters (volts/turn or whatever), you're better off doing it analytically with the simple ratio I provided above. SPICE doesn't solve your problems for you, it just tells you how wrong your guess is...

In short, no. Initial permeability is way off, that's all.

Not really.

The MOSFETs run just as cool in a properly designed ~100kHz circuit, and the ferrite core will be cheaper, smaller and run cooler. (Typical ETD25ish core will do well over 250W at ~100kHz, and might cost $10 from most suppliers, not $50.)

The ferrite may be brittle, but if you dropped that big toroid on a concrete floor, the sharp corners of the core would bite right through the windings. The smaller package means it's easier to put inside a chassis which deflects blows, or it could be potted without excessive expense (still, potting compound isn't cheap!).

The electronics will be exactly as simple either way if you don't mind a design without any ruggedization. I haven't looked at your LTSpice circuit but I'm guessing it's little more than a chopper. What happens if someone shorts the output? Excessive input voltage? Reverse input voltage? How about EMI/RFI performance -- snubbing, filtering, common mode noise?

A current mode controller isn't too difficult to design and build (or get an OTS chip to do it), but all the protection and filtering gets tedious. Pretty soon you have a bucket of $1 parts that, for whatever reason, costs about,

...About that!

The efficiency could be higher, but that's not bad as conversion goes.

Tim

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

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  • Yes, 98.6% does sound a bit low.

  • Input standby power to the transformer (ie: NO load on transformer) should be a few watts at most.

===================== Snipped for brevity

Reply to
Robert Baer

Duh :)

When I deleted the connection from the secondary to the diodes, the node =

numbers shifted. I changed the schematic by adding labels to the = important=20 nodes. Now it makes a lot more sense!

Thanks,

Paul=20

Reply to
P E Schoen

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About 8 turns per (RMS) volt, which is rule of thumb for "cooking" transformer iron, with 60Hz sinusoidal excitation. Probably won't be any good at 600, let alone 1000Hz.

Square wave makes things worse. The iron won't be suitable for your application. You need thin (.003") mumetal or ferrite.

Running your simulation, I see 1600 amps peak in the FETs, and the primary, under load. That won't reflect real life.

VA in one direction equals VA in the other direction. TANSTAAFL.

I won't argue with that ;-)

You need a better transformer model, including the characteristics of the iron. There's an ideal transformer model that comes with LTspice, that you can adapt by shunting the primary with a hysteretic model inductor (RTFM).

In a nutshell:

Your model is not adequate.

Your iron isn't up to the job.

Use ferrite. Something like Epcos E cores in N97 material, or a toroid in N49.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)
Reply to
Fred Abse

Yes, BTDT. I now label the important nodes that I want to track. Once labelled, they don't change.

Reply to
John S

That was down to the goddamn Greek mu. There was one I hadn't spotted (C1). They don't travel well on Usenet. Apart from inrush, current now looks sensible.

You really need to check the "convert Greek mu" in Netlist options for stuff posted to Usenet.

I still don't think it will work as expected at 600/1000 with that iron.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)
Reply to
Fred Abse

transformer_kits.htm,

Losses at higher frequencies is probably going to be key, yes.

Eddy current losses go up with frequency for a given core conductance (or lamination thickness). Your core is made both to work at 60Hz and to be convenient to wind, so you may luck out on the eddy current losses if they needed thinner laminations just to make it mechanically convenient to wind.

Hysteresis losses at a given flux density pretty much go as a constant energy per cycle -- and you're intending to cycle 10 or 20 times faster, which is going to push those losses up dramatically. Again, you might luck out if they were low to start with -- but will you?

I just don't see the wisdom of using some random surplus transformer core that's designed for 60Hz usage when you could obtain a purpose-designed E- core and use it at a much higher frequency. You're going to spend a lot of time puttering around with this, and you're almost guaranteed that you're not going to get 10x the power handling out of the thing with a

10x increase in frequency. 
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply to
Tim Wescott

"Fred Abse" wrote in message=20 news: snipped-for-privacy@invalid.invalid...

I didn't know about that. It is now checked.

iron.

I agree that this may not be a very practical design. I made a new = circuit=20 which limits the MOSFET current to about 90 amps, but now instead of = having=20

1000 amps inrush, I have about 1000 watts. I used a 30 ohm load to get = 750=20 watts output.

So I added an inductor (470 mH) to the output, which reduces the power = to=20 acceptable levels during startup, but it also adds weight, size, and = cost.=20 The current limit transistors might not be needed in this case.

I also tried it with an extreme overload of one ohm. The power in each=20 MOSFET becomes 416 watts. Not good. And the output current is 6.7 amps=20 rather than the normal 4.5. So I really need better overcurrent and = short=20 circuit protection.

The high start-up current is due to the output capacitor. So I added a=20 current limiting resistor and discharge diode, which seems to work=20 acceptably.

Maybe I will still build the basic design and try it using the toroid, = just=20 to see how well (or not) it works. The current limit transistors are not =

really needed if I limit the capacitor charge current. So that will = simplify=20 the circuit and still keep things in a safe range. I can try a light = load=20 first, then go for the maximum. I have some 2000 watt heaters 220V which = are=20 about 26 ohms, so that will give me close to the 750 watt target. I = think=20 I'll enclose it in a steel box in case anything explodes.

Then, I change the transformer to one using ferrite. I bought some big E =

cores and bobbins some time ago. They are something like 3" square, and=20 probably good for several kW. I'll probably design it for 160 / 320 VDC = and=20

12 VDC input so I can use a single battery to get enough voltage for the = DC=20 bus in my 2 HP 240V 3 phase motor drive. I just want to see how well the =

combination runs a 1.5 HP motor. And it may be handy to have a portable=20 three phase source.

Thanks,

Paul

(Here's the modified circuit: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

Version 4 SHEET 1 896 680 WIRE -96 80 -144 80 WIRE 128 80 -96 80 WIRE 304 128 224 128 WIRE 320 128 304 128 WIRE 416 128 384 128 WIRE 560 128 496 128 WIRE 592 128 560 128 WIRE 224 160 224 128 WIRE -592 176 -672 176 WIRE -544 176 -592 176 WIRE -256 176 -544 176 WIRE 16 176 -256 176 WIRE 128 176 128 160 WIRE 128 176 16 176 WIRE 128 192 128 176 WIRE 496 192 496 128 WIRE 320 208 272 208 WIRE 416 208 416 128 WIRE 416 208 384 208 WIRE 592 208 592 128 WIRE -352 224 -368 224 WIRE -64 224 -272 224 WIRE 16 240 16 176 WIRE -432 256 -496 256 WIRE 496 256 448 256 WIRE -368 272 -368 224 WIRE -256 272 -256 176 WIRE 128 272 112 272 WIRE -144 288 -144 80 WIRE 112 288 112 272 WIRE 224 288 224 240 WIRE 272 288 272 208 WIRE 272 288 224 288 WIRE 320 288 272 288 WIRE 416 288 384 288 WIRE 496 288 496 256 WIRE -496 304 -496 256 WIRE 448 304 448 256 WIRE -64 336 -64 224 WIRE 48 336 -64 336 WIRE -592 368 -592 176 WIRE -432 368 -432 256 WIRE -192 368 -400 368 WIRE 48 368 48 336 WIRE 64 368 48 368 WIRE 304 368 304 128 WIRE 320 368 304 368 WIRE 416 368 416 288 WIRE 416 368 384 368 WIRE 448 368 416 368 WIRE 496 368 448 368 WIRE 592 368 592 288 WIRE 592 368 496 368 WIRE 704 368 592 368 WIRE 160 384 112 384 WIRE 704 400 704 368 WIRE -672 416 -672 176 WIRE -256 416 -256 352 WIRE -240 416 -256 416 WIRE -144 416 -144 384 WIRE -144 416 -160 416 WIRE 16 416 16 320 WIRE 32 416 16 416 WIRE 160 416 160 384 WIRE 160 416 112 416 WIRE -144 432 -144 416 WIRE -400 448 -400 368 WIRE -400 448 -432 448 WIRE -256 448 -256 416 WIRE 16 448 16 416 WIRE 16 448 0 448 WIRE 160 448 160 416 WIRE -672 528 -672 480 WIRE -592 528 -592 448 WIRE -592 528 -672 528 WIRE -496 528 -496 384 WIRE -496 528 -592 528 WIRE -368 528 -368 352 WIRE -368 528 -496 528 WIRE -320 528 -320 496 WIRE -320 528 -368 528 WIRE -144 528 -144 512 WIRE -144 528 -320 528 WIRE -64 528 -64 496 WIRE -64 528 -144 528 WIRE 48 528 -64 528 WIRE 160 528 48 528 WIRE 48 592 48 528 FLAG 48 592 0 FLAG 704 400 0 FLAG 560 128 Vout FLAG -544 176 in FLAG -96 80 dr1 FLAG 112 272 dr2 SYMBOL ind2 112 64 R0 SYMATTR InstName L1 SYMATTR Value 180u SYMATTR Type ind SYMATTR SpiceLine Rser=3D10u SYMBOL ind2 112 176 R0 SYMATTR InstName L2 SYMATTR Value 180u SYMATTR Type ind SYMATTR SpiceLine Rser=3D10u SYMBOL ind2 240 144 M0 WINDOW 0 -19 22 Left 2 WINDOW 3 -46 46 Left 2 SYMATTR InstName L3 SYMATTR Value 32m SYMATTR Type ind SYMATTR SpiceLine Rser=3D200u SYMBOL nmos -192 288 R0 WINDOW 3 53 65 Left 2 SYMATTR Value IRF2903ZS SYMATTR InstName M1 SYMBOL nmos 64 288 R0 WINDOW 3 56 67 Left 2 WINDOW 0 59 38 Left 2 SYMATTR Value IRF2903ZS SYMATTR InstName M2 SYMBOL voltage -592 352 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 132 Left 2 SYMATTR SpiceLine Rser=3D2m SYMATTR InstName V1 SYMATTR Value 12 SYMBOL diode 384 304 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value MUR460 SYMBOL diode 320 224 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value MUR460 SYMBOL polcap 480 192 R0 WINDOW 3 32 56 Left 2 SYMATTR Value 470u SYMATTR InstName C1 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D600 Irms=3D2.9 Rser=3D0.018 Lser=3D0 SYMBOL res 576 192 R0 SYMATTR InstName R1 SYMATTR Value 30 SYMBOL voltage -496 288 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -43 57 Left 2 WINDOW 3 -194 303 Left 2 SYMATTR SpiceLine Rser=3D50m SYMATTR Value PULSE(0 10 250u 10n 10n 450u 1000u 100) SYMATTR InstName V2 SYMBOL voltage -368 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -48 62 Left 2 WINDOW 3 -322 296 Left 2 SYMATTR SpiceLine Rser=3D50m SYMATTR Value PULSE(0 10 762u 10n 10n 450u 1000u 100) SYMATTR InstName V3 SYMBOL diode 320 144 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL diode 384 384 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D4 SYMATTR Value MUR460 SYMBOL polcap -688 416 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 10u SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D25 Irms=3D2.9 Rser=3D100m Lser=3D0 SYMBOL res -160 416 R0 SYMATTR InstName R2 SYMATTR Value 2.5m SYMBOL res 144 432 R0 SYMATTR InstName R3 SYMATTR Value 2.5m SYMBOL res -256 208 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 100 SYMBOL res -416 464 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R5 SYMATTR Value 100 SYMBOL npn -256 400 M0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL npn 0 400 M0 WINDOW 3 -43 97 Left 2 SYMATTR Value 2N3904 SYMATTR InstName Q2 SYMBOL res -144 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 100 SYMBOL res -240 368 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R7 SYMATTR Value 2k SYMBOL res 128 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 100 SYMBOL res 32 336 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R9 SYMATTR Value 2k SYMBOL ind 400 144 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L4 SYMATTR Value 1n SYMBOL res 480 272 R0 SYMATTR InstName R10 SYMATTR Value 30 SYMBOL diode 432 368 M180 WINDOW 0 24 64 Left 2 WINDOW 3 7 -24 Left 2 SYMATTR InstName D5 SYMATTR Value MUR460 TEXT 144 304 Left 2 !K1 L1 L2 L3 1 TEXT -584 624 Left 2 !.tran 0 200m 0 1u startup TEXT 320 456 Left 2 ;Primary 2x8 turns 2V/turn at 1000 Hz TEXT 320 528 Left 2 ;25 A peak magnetizing current for 180u 1kHz TEXT 336 560 Left 2 ;77 A peak current at 30 ohm load TEXT 320 496 Left 2 ;Secondary 100 turns 2V/turn at 1000 Hz=20

Reply to
P E Schoen

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What is the 12Vdc supply? The best vehicle battery I've seen barely does 300 to 500A into a dead short. That calculates to more like 20m, not 2m Rseries. Especially at start up inrush currents.

Reply to
Robert Macy

Yes, that is more reasonable. And for my prototype I plan to use a = booster=20 battery and connection through a cigarette lighter jack so the contact=20 resistance and the wires will probably have enough resistance (and=20 inductance) to limit the surges to under 100A. Also, the output filter=20 capacitor will probably have higher ESR than what is in the simulation=20 model. With real components, I would expect less current surges.

My current limiting scheme is fatally flawed because it puts the MOSFETs =

into a linear mode which burns a lot of power. As a simple improvement, = I=20 wonder if a 556 dual timer could be set up with a 200 mV threshold and =

50A=20 100mV shunts (2 milliohm) so that the MOSFET would be turned off = completely=20 when 100 amps is reached. But it would need to be latched on until the = drive=20 reverses. This could probably be done by connecting the trigger to the = gate=20 drive signal. But then maybe I should do it all with a PIC, or a PWM=20 controller like an SG3526.

Mostly I just want to see just what the performance of the toroid will = be at=20

1kHz. So I just need a 12V square wave good for about 50A. A 600 watt=20 amplifier? Or maybe it would be better to reverse drive the transformer. = I=20 could use my VF motor drive to get 400 Hz, but that's PWM, with a 15 kHz =

carrier.

What I may want to look at are spot welding transformers. From what I = can=20 tell, they use a toroid and 1000 Hz, and a 32 kVA (20% duty cycle) unit = is=20

19kG, so a 1kVA continuous version would probably be less than 5kG:
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nical-data
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transformers

I do not think these are ferrite. They might be powdered iron, but I = think=20 they are tape wound toroids. Here are some that are rated at 50-2500 Hz, = and=20 from 5 to 5000 kVA!

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Here is some information on some types of steel laminations used for = various=20 frequency ranges:

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Even the C-97 power transformer laminations (14 mil) are shown as good = up to=20 about 800 Hz. And the C-95 (5 mil) are good up to 7 kHz for power=20 applications.

Here is some information on typical toroid transformers=20

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where it shows core loss to be = about 1%=20 of VA rating at 60 Hz. I might expect it to be perhaps no more than 20% = at=20

1kHz then. The E-I transformer was about 20% core loss, so clearly not=20 usable at even 300 Hz.

This seems useful:

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For the toroid transformer I have, the no-load core loss at 60 Hz is = about=20

0.5%, so I think it will be good at 1000 Hz:
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And here are some steel core materials good up to 50 kHz:

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Paul

Reply to
P E Schoen

"P E Schoen" wrote in message news:jih0rq$m19$ snipped-for-privacy@dont-email.me...

OK, I made a circuit as described with two 555 timers. It seems to work=20 well, and the current limit is such that it folds back to only a few = watts=20 with an overload (I used 1 ohm). I may need to provide a more stable=20 reference voltage than the 12V supply, however. The CV for the timer is=20 about 200 mV, which gives a threshold of 200 mV or 100 amps on the 100mV =

50A=20 shunts. But I don't know if a real 555 will work at such a low voltage. = The=20 schematic for the threshold comparator shows two diode drops to the = common=20 resistor. The CMOS version may have a comparator that includes ground. = Some=20 schematics show both PNP and NPN transistors.

Paul

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D

Version 4 SHEET 1 896 680 WIRE -432 0 -1088 0 WIRE -672 32 -1056 32 WIRE -96 80 -144 80 WIRE 128 80 -96 80 WIRE -992 112 -1024 112 WIRE -672 112 -672 32 WIRE -672 112 -768 112 WIRE 304 128 224 128 WIRE 320 128 304 128 WIRE 416 128 384 128 WIRE 496 128 416 128 WIRE 560 128 496 128 WIRE 592 128 560 128 WIRE -400 144 -720 144 WIRE 224 160 224 128 WIRE -1088 176 -1088 0 WIRE -992 176 -1088 176 WIRE -720 176 -720 144 WIRE -720 176 -768 176 WIRE -672 176 -672 112 WIRE -592 176 -672 176 WIRE -544 176 -592 176 WIRE 128 176 128 160 WIRE 128 176 -544 176 WIRE 128 192 128 176 WIRE 496 192 496 128 WIRE 320 208 272 208 WIRE 416 208 416 128 WIRE 416 208 384 208 WIRE 592 208 592 128 WIRE -112 224 -320 224 WIRE -16 224 -32 224 WIRE -256 240 -768 240 WIRE -432 256 -432 0 WIRE -432 256 -496 256 WIRE 496 256 464 256 WIRE -320 272 -320 224 WIRE 128 272 112 272 WIRE 464 272 464 256 WIRE -144 288 -144 80 WIRE 112 288 112 272 WIRE 224 288 224 240 WIRE 272 288 272 208 WIRE 272 288 224 288 WIRE 320 288 272 288 WIRE 416 288 384 288 WIRE -1056 304 -1056 32 WIRE -992 304 -1056 304 WIRE -704 304 -768 304 WIRE -496 304 -496 256 WIRE -16 336 -16 224 WIRE 48 336 -16 336 WIRE -1216 352 -1264 352 WIRE -1168 352 -1216 352 WIRE -704 352 -704 304 WIRE -704 352 -1168 352 WIRE -592 368 -592 176 WIRE -432 368 -432 256 WIRE -400 368 -400 144 WIRE -192 368 -400 368 WIRE 48 368 48 336 WIRE 64 368 48 368 WIRE 304 368 304 128 WIRE 320 368 304 368 WIRE 416 368 416 288 WIRE 416 368 384 368 WIRE 464 368 464 336 WIRE 464 368 416 368 WIRE 496 368 496 336 WIRE 496 368 464 368 WIRE 592 368 592 288 WIRE 592 368 496 368 WIRE 704 368 592 368 WIRE 160 384 112 384 WIRE -1024 400 -1024 112 WIRE -992 400 -1024 400 WIRE -672 400 -672 176 WIRE -672 400 -768 400 WIRE 704 400 704 368 WIRE -672 416 -672 400 WIRE -256 416 -256 240 WIRE -240 416 -256 416 WIRE -144 416 -144 384 WIRE -144 416 -160 416 WIRE 32 416 16 416 WIRE 160 416 160 384 WIRE 160 416 112 416 WIRE -144 432 -144 416 WIRE -400 448 -400 368 WIRE -400 448 -432 448 WIRE 160 448 160 416 WIRE -1264 464 -1264 352 WIRE -1168 464 -1168 352 WIRE -992 464 -1088 464 WIRE -688 464 -768 464 WIRE -720 528 -768 528 WIRE -672 528 -672 480 WIRE -592 528 -592 448 WIRE -592 528 -672 528 WIRE -496 528 -496 384 WIRE -496 528 -592 528 WIRE -320 528 -320 352 WIRE -320 528 -496 528 WIRE -144 528 -144 512 WIRE -144 528 -320 528 WIRE 48 528 -144 528 WIRE 160 528 48 528 WIRE -688 544 -688 464 WIRE -16 544 -16 336 WIRE -16 544 -688 544 WIRE -720 560 -720 528 WIRE 16 560 16 416 WIRE 16 560 -720 560 WIRE -1056 592 -1056 304 WIRE -992 592 -1056 592 WIRE -704 592 -704 352 WIRE -704 592 -768 592 WIRE 48 592 48 528 WIRE -1264 640 -1264 528 WIRE -1168 640 -1168 544 WIRE -1168 640 -1264 640 WIRE -1024 640 -1024 400 WIRE -1024 640 -1168 640 WIRE -672 640 -672 528 WIRE -672 640 -1024 640 WIRE -1088 672 -1088 464 WIRE -112 672 -112 224 WIRE -112 672 -1088 672 FLAG 48 592 0 FLAG 704 400 0 FLAG 560 128 Vout FLAG -544 176 in FLAG -96 80 dr1 FLAG 112 272 dr2 FLAG -1216 352 CV SYMBOL ind2 112 64 R0 SYMATTR InstName L1 SYMATTR Value 180u SYMATTR Type ind SYMATTR SpiceLine Rser=3D10u SYMBOL ind2 112 176 R0 SYMATTR InstName L2 SYMATTR Value 180u SYMATTR Type ind SYMATTR SpiceLine Rser=3D10u SYMBOL ind2 240 144 M0 WINDOW 0 -19 22 Left 2 WINDOW 3 -46 46 Left 2 SYMATTR InstName L3 SYMATTR Value 32m SYMATTR Type ind SYMATTR SpiceLine Rser=3D200u SYMBOL nmos -192 288 R0 WINDOW 3 53 65 Left 2 SYMATTR Value IRF2903ZS SYMATTR InstName M1 SYMBOL nmos 64 288 R0 WINDOW 3 56 67 Left 2 WINDOW 0 59 38 Left 2 SYMATTR Value IRF2903ZS SYMATTR InstName M2 SYMBOL voltage -592 352 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 132 Left 2 SYMATTR SpiceLine Rser=3D20m SYMATTR InstName V1 SYMATTR Value 12 SYMBOL diode 384 304 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value MUR460 SYMBOL diode 320 224 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value MUR460 SYMBOL polcap 480 192 R0 WINDOW 3 32 56 Left 2 SYMATTR Value 470u SYMATTR InstName C1 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D200 Irms=3D50 Rser=3D0.05 Lser=3D0 SYMBOL res 576 192 R0 SYMATTR InstName R1 SYMATTR Value 30 SYMBOL voltage -496 288 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -43 57 Left 2 WINDOW 3 -194 303 Left 2 SYMATTR Value PULSE(0 10 250u 10n 10n 450u 1000u 100) SYMATTR InstName V2 SYMBOL voltage -320 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -48 62 Left 2 WINDOW 3 -322 296 Left 2 SYMATTR Value PULSE(0 10 762u 10n 10n 450u 1000u 100) SYMATTR InstName V3 SYMBOL diode 320 144 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL diode 384 384 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D4 SYMATTR Value MUR460 SYMBOL polcap -688 416 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 10u SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D25 Irms=3D2.9 Rser=3D100m Lser=3D0 SYMBOL res -160 416 R0 SYMATTR InstName R2 SYMATTR Value 2m SYMBOL res 144 432 R0 SYMATTR InstName R3 SYMATTR Value 2m SYMBOL res -16 208 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 100 SYMBOL res -416 464 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R5 SYMATTR Value 100 SYMBOL res -144 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 100 SYMBOL res 128 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 100 SYMBOL Misc\\NE555 -880 208 R0 SYMATTR InstName U1 SYMBOL Misc\\NE555 -880 496 R0 SYMATTR InstName U2 SYMBOL res -1152 560 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R7 SYMATTR Value 50 SYMBOL polcap -1280 464 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 10u SYMATTR InstName C3 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D25 Irms=3D2.9 Rser=3D100m Lser=3D0 SYMBOL res 480 240 R0 SYMATTR InstName R9 SYMATTR Value 30 SYMBOL diode 448 336 M180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D5 SYMATTR Value MUR460 TEXT 144 304 Left 2 !K1 L1 L2 L3 1 TEXT -584 624 Left 2 !.tran 0 200m 0 1u startup TEXT 320 456 Left 2 ;Primary 2x8 turns 2V/turn at 1000 Hz TEXT 320 528 Left 2 ;25 A peak magnetizing current for 180u 1kHz TEXT 336 560 Left 2 ;110 A peak current limit TEXT 320 496 Left 2 ;Secondary 100 turns 2V/turn at 1000 Hz

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P E Schoen

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