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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I have been reading every document related to ferrite transformers (again) as steve connor suggested, however i still have trouble understanding the complexities of transformer design.
first, I will use ferrite because I need AC. Second, as I increase Frequency i must Decrease my delta B right? Third, my datasheets saturation B [Absolute value], and my Delta B are different right, Delta B should be smaller at high freq then at a lower freq? right?
Thus the heating becomes the limiting factor right? not the saturation.
Next, how can I calculate max power after my design is complete? (when I say calculate, I mean Predict like +- 30%, does not need to be perfect). My goal is like 1kw to 1.5 kw or so...
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Patrick wrote ...
Second, as I increase Frequency i must Decrease my delta B right?
Not necessarily. It depends where you are on the curves, what your design goals are, and how much loss you can tolerate.
wrote ...
Third, my datasheets saturation B [Absolute value], and my Delta B are different right, Delta B should be smaller at high freq then at a lower freq? right?
Firstly I think it's less confusing to speak in terms of peak B - it's understood that you're dealing with AC and that the flux will generally swing equally in both directions.
Second, I assume you're familiar with the "universal EMF equation" or whatever you want to call it, which relates most of the parameters of interest. For sine waves, it's:
E = 4.44 * f * N * Ac * B
where E = volts rms, f = frequency in Hz, Ac = core area in square meters, and B = peak flux density in Tesla.
For example, if your core cross-sectional area is 1 square inch (6.45E-4 m^2), then, if you drive it at, say, 25 kHz at 10 Vrms per turn, your peak flux density B will be about 0.14 T.
From the manufacturer's data on the core, you should be able to roughly determine the core loss at 25 kHz and 0.14 T; is the loss acceptable?
Then, given the wire size you'll be using to accommodate the current you need, check to see if it looks like you'll have enough winding area to fit the number of turns (of course you also have to account for insulation).
Now maybe you don't have enough room for the windings and insulation under these drive conditions, and core losses are very low, so go back and change the numbers a little bit - how about 30 kHz and 0.2T? Now you're at about 17 Vrms/turn, will that work?
It's an iterative process.
wrote ...
Thus the heating becomes the limiting factor right? not the saturation.
Generally speaking, yes.
wrote ...
Next, how can I calculate max power after my design is complete? (when I say calculate, I mean Predict like +- 30%, does not need to be perfect). My goal is like 1kw to 1.5 kw or so...
Any help is appreciated.
Well basically the power throughput of the transformer will be determined simply by the volts-per-turn drive level (which as per the above depends on F and B), and the number of turns you can fit into your winding area (and of course the number of turns depends on the size of the wire you're using, which depends on the current; the amount of insulation; and the area available for the windings). 1 to 1.5 kw should be no problem at all.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ooooo, yes i see , ah crap im late for physics 2A ill be back later...
Ok im back let me make some calculations....
Ok, im using a PWM square wave, so my derivation of EMF should be:
Bmax = Vpk * 10^8 / 4N * Ac * F in Gauss.
right?
Ok, Ive done some math, but still have questions: First, does power throughput vary with frequency directly or incidently? (I would like the highest power at lowest frequency possible.) Second, at my desired Bpk my Oersteds are high but still on the B-H curve: so does Oersteds matter or not? I do see that as Teslas and Oersteds go up I lose more power in the core and through clamping snubbers. is heating and loss the only concern for H? I can tolerate a lot of heat loss as I am using an oil-Pump-Radiator design for super duper high power, efficiency can come later.
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Question About Ferrite, delta B, and Frequency....
