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Old 27th May 2011, 08:45 AM   #21
sekhar is offline sekhar  India
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guys i did the pain staking calculation ................ from the book luka referred me to .......

calculation:-

skin depth = 6.62/ root of frequency = .0.0209cm
wire diameter = 2 X skin depth = 0.209 X 2 = 0.48cm ~ 26SWG.
bare wire diameter Aw = 3.14D^2/4 = 0.00137
I/P power Pin = Po/n = 400/0.95 = 421W
Ipk = pin X 1.414 /Vin(min) = 421 X 1.414 / 90 = 6.61A
Ripple current = 0.2Ipk = 1.323 A
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Old 27th May 2011, 08:58 AM   #22
sekhar is offline sekhar  India
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max duty cycle Dmax = (Vo - (Vin X 1.414))/Vo = 0.68

Inductance L = (Vin(min) X 1.414)Dmax/ ripple current X frequency = .000685H
energy Required Eng = LIpk^2/2 = 0.0149 (watt-second).
electrical cofficient Ke= 0.145PoBm^2/10000 = .0003625.
core geometry coefficient Kg = (Eng)^2/ Ke X a = 0.615{cm^5}
ok here is a slight problem the Kg value suggets me use a bigger core say ETD49 or so wat happens if I use a smaller core say ETD34.

Last edited by sekhar; 27th May 2011 at 09:20 AM.
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Old 27th May 2011, 09:05 AM   #23
sekhar is offline sekhar  India
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lets proceed with ETD34 .....................

current density J =2(Eng)(10000)/Bin X Ap X Ku =1233A/cm^2

this also seems very high...........
neways lets proceed.............
Irms = Ipk/1.414 = 4.67A
bare wire area Aw(n) = 4.67/1233 = .00394 cm^2.
number of strands Sn = Aw(n)/ area of 26SWG wie = 3.07 ~ 3
number of turns = Wa X Ku /Sn X (area of 26SWG wire) = 129.
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Old 27th May 2011, 09:11 AM   #24
sekhar is offline sekhar  India
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calculate air gap Lg = (0.4 X 3.14 X N^2 X Ae)/L X 100000000 = 0.2971cm or 117mils...
fringe flux F =(1 + (Lg/root of Ae)ln(2G/Lg)) = 1.692.... little mistake due to log ......

new number of turns = root of{(Lg X L)/0.4 X 3.14 X Ae X F X (10^-8)} = 99.36 ~ 99
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Old 27th May 2011, 09:20 AM   #25
sekhar is offline sekhar  India
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cal Bpk = F[{(0.4 X 3.14 X N X Ipk(10^-4)}/Lg] = 0.468

new resistance per cm = 1345/Sn = 448.33

winding resistance R = (MLT) N 448.33 (10^-6) = 0.315E
copper loss Pcu = Irms^2 X R = 6.86W.
Regulation a = Pcu/Po =1.717%
Ac flux density Bac = 0.02768T
core loss Pfc=0.018W
total loss =Pcu +Pfc = 6.878W
Temperature Rise = Tr = 82.35C


these things dont seem to be in place ...................

tell me if i had some mistakes...........

regards
sekhar
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Old 27th May 2011, 01:40 PM   #26
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...ermh..., I guess you did not mean 0.48cm, but 0.48mm...

Anyway, please note that the skin effect as calculated in your formulas is valid for a single wire in free space only. Practically this calculation does still fit in single layer windings, and more or less in two layer windings. But not for a massive bunch of conductors.
You will need to consider the proximity effect, which is the extended consequence from the skin effect, when going for multiple conductors.
The skin effect only takes into account the self induced effects of one wire.
The proximity effect additionally takes into account the fields which are caused by the other conductors close by. You may search the web for graphs, which indicate Rac/Rdc for typical winding arrangements depending on frequency.
Furtheron you are neglecting the eddy current losses, which are caused in the winding by the fringing field of the core. Sorry, I do not have a practical calculation model on hand, without finite elements.
You can be sure that you will have more losses than your calculation indicates.

What happens if you chose an etd34 instead of etd49?
More losses than with an etd 49, and consequently much more temperature rise than with an etd49.

New calculation of turns:
Forget it.
a) Your wild formula with a mixture of factors and units seems to be intended for pure AC flux situations with pos an neg flux. But your PFC will have only one flux polarity in the core, no sign reversal. ==> Giving you a factor-two-error for the number of turns.
a) Simplified fringing field calculations tend to indicate an accuracy, which is simply not there.
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Old 27th May 2011, 02:50 PM   #27
sekhar is offline sekhar  India
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Quote:
Originally Posted by ChocoHolic View Post
...ermh..., I guess you did not mean 0.48cm, but 0.48mm...

Anyway, please note that the skin effect as calculated in your formulas is valid for a single wire in free space only. Practically this calculation does still fit in single layer windings, and more or less in two layer windings. But not for a massive bunch of conductors.
You will need to consider the proximity effect, which is the extended consequence from the skin effect, when going for multiple conductors.
The skin effect only takes into account the self induced effects of one wire.
The proximity effect additionally takes into account the fields which are caused by the other conductors close by. You may search the web for graphs, which indicate Rac/Rdc for typical winding arrangements depending on frequency.
Furtheron you are neglecting the eddy current losses, which are caused in the winding by the fringing field of the core. Sorry, I do not have a practical calculation model on hand, without finite elements.
You can be sure that you will have more losses than your calculation indicates.

What happens if you chose an etd34 instead of etd49?
More losses than with an etd 49, and consequently much more temperature rise than with an etd49.

New calculation of turns:
Forget it.
a) Your wild formula with a mixture of factors and units seems to be intended for pure AC flux situations with pos an neg flux. But your PFC will have only one flux polarity in the core, no sign reversal. ==> Giving you a factor-two-error for the number of turns.
a) Simplified fringing field calculations tend to indicate an accuracy, which is simply not there.
i know that that things r nt as they should be .......... but with the given amount of knowledge............ that i have i was able to put down this number with the help of luka........
So should i go forward with this design or should i sit back do some more studying.................

regards
sekhar
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Old 27th May 2011, 03:04 PM   #28
sekhar is offline sekhar  India
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@choholic
ok lets start the calculation all over again ........................ u tell me wat to do i will give all my input data, and lets see if can get this thing right atleast on paper......... then I will try making it ..............
and thanks again for pointing out my mistakes.................
and here is the schematic for the pfc

regards
sekhar
Attached Files
File Type: pdf pfc.pdf (21.6 KB, 70 views)
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Old 28th May 2011, 03:16 PM   #29
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Quote:
Originally Posted by sekhar View Post
@choholic
... u tell me wat to do i will give all my input data, and lets see if can get this thing right atleast on paper......... then I will try making it ..............
...means I a shall design your PFC, explain every step and then debug it for you...

Sorry, I am out of the game.
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Old 28th May 2011, 04:01 PM   #30
sekhar is offline sekhar  India
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Join Date: Jul 2009
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Quote:
Originally Posted by ChocoHolic View Post
...means I a shall design your PFC, explain every step and then debug it for you...

Sorry, I am out of the game.
i just wanted that u to help me ................ nothing that u have to take the entire burden on ur shoulder.............i will do everything just needed guidance.......neways thanks for help

regards
sekhar
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