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I could have sworn the voltage on the spreadsheet was 325Vish, has it been changed? That's the main reason my numbers are wrong.
Yes, sorry. I was mucking around to see how many more primary turns I'd need running a sine wave inverter. The peak DC voltage I can use is ~460V, so that'd make ~325VAC unless I'm driving it with a square wave.
Wastrel wrote ...
I have the feeling that the capacitor this is going to need will be huge, and the current requirement will make it expensive.
I've got hundreds of 450V 470-1000uF Nippon Chemi-Con capacitors of various types, so that's not an issue. It'll take 5000uF for 5%/20V ripple. To reduce ripple further, it might be cheaper to add another boost converter -> ~450V after the PFC boost stage, instead of trying to throw bulk capacitance at the problem.
Wastrel wrote ...
The energy wasted is quite flat and I think it's to do with how you are calculating copper used. Fixed diameter wire, single winding. I think if you wind more copper on the core the power wasted will drop. Tape for the primary for example. This may make it optimal to use a lower frequency than 400hz and radiate much less total heat.
More turns = less core losses, more copper losses. Larger diameter = less copper losses, more winding space used/more layers for a given number of turns. I've heard that designing for core losses ~= copper losses at full load is good, although I don't understand why.
I can't get a 50Hz design which'll actually fit in the winding window with reasonable losses. 200Hz works out okay, but losses are still higher for a given amount of copper than running at 400Hz unless I've screwed up the calculations. 1000Hz is even better, but I'm not sure if it's worth it due to needing more layers of mylar and increased switching losses.
Wastrel wrote ...
You know about interleaving primary and secondary windings, right? This will be harder given the secondary voltage.
Don't think this is possible with the materials I have available and the insulation requirements.
Wastrel wrote ...
I'm surprised splitting the cores isn't better, but then the main advantage would be to use more copper. I'd also consider hacksawing away some of the inner ring, which would cost you some area but open up the winding window a lot.
How did you calculate the cross sectional area of core you needed for 15kva? I know you are in the right ball park for 50Hz operation but I'm quite fuzzy on the actual maths for that. You may have much more metal than you need for 400Hz (are proportionally more hysteresis loss).
Calculated by mucking around with some calculations based on the same equations in the sheet. I don't have the working for that now.
Wastrel wrote ...
My transformer theory is weak as I said, I have done a lot of reading for a core of my own and I know enough to know I don't know what I'm talking about. Some things I think are generally true are that toroidal cores are good for low leakage of flux and can have a huge winding window compared to E cores, but that you pay a heavy price if you don't fill most of it with copper.
You're right about the low leakage. The winding window here is quite small due to the low ID.
Wastrel wrote ...
Something else I think is true is that for a resistive load your copper losses should be highest when the load draws full current, and the core losses should be highest when the load draws no current. This make sense to you?
Core losses are fixed, copper losses are vary with the square of the current. At full load I think they should be about equal.
Hi Newton, thanks for chiming in.
Newton Brawn wrote ...
Ross First let us know: Service factor: 1 for continuous service at full load, 0,5 for work 5 minutes in a period of 10 minutes, 0.2 for working 2 minutes in a period of 10 minutes.
Service factor = 1
Newton Brawn wrote ...
(Welding machines transformers are designed for .2~.5 service factor) Second : Do you have intention of add a small fan to cool the core ?
Yes, I was planning to use a 240mm fan.
Newton Brawn wrote ...
Third: Use all units as IS system. m for meter, kg for weight, T for tesla, V for volt A for amper Etc Do not play with gauss, oersted, gilberts, centimeter, inch, pound, once, inch etc etc Third: Define yours design parameters
I should have written design parameters in from the start, thanks for mentioning this. There's now a new link in the first post. I've probably missed some important parameters, sorry.
All the units in the sheets should be SI, although I've used C instead of K for temperature, and mm instead of m for wire gauge as those are more commonly used/easier to understand at a glance.
Sorry for the late replies, I've been busy studying for/sitting exams recently.
Registered Member #39190
Joined: Sat Oct 26 2013, 09:15AM
Location: Boise National Forest
Posts: 65
Ross Allan wrote ... Could have PFC stage boost to 565VDC instead, and then full bridge -> 400VAC sine wave. Don't think it's worth it, as the reduction in core losses will probably be less than the increase in switching losses.
But switching losses would be a lot easier to dissipate. Driving the transformer with a sinewave seems like a great idea.
Ross Allan wrote ... Could have PFC stage boost to 565VDC instead, and then full bridge -> 400VAC sine wave. Don't think it's worth it, as the reduction in core losses will probably be less than the increase in switching losses.
But switching losses would be a lot easier to dissipate. Driving the transformer with a sinewave seems like a great idea.
That's a good point.
Does anyone know a good place to get high copper weight PCBs manufactured in low/volume prototype? Looking for >= 8oz/ft^2 (280 μm).
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
From experience, winding one transformer using two cores will have less copper loss than two separate transformers, but I would wind two 5kV transformers rather than one 10kV transformer etc because;
The option of full voltage.current with secondaries in series can be re-wired as half the voltage at twice the current
or as 5-0-5 kV which is easier to insulate than 0 - 10 kV
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Toroidal Transformer Design
