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Old 23rd November 2011, 08:54 AM   #31
AndrewT is offline AndrewT  Scotland
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swgs awgs inches, millimetres, drill numbers, drill letters.
I used to have the five column table hung on the wall behind my lathe.

this one shows swg awg mm
Imperial Standard Wire Gauge to American Wire Gauge Comparison Table
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Old 23rd November 2011, 10:08 AM   #32
AJT is offline AJT  Philippines
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Quote:
that winding machine is a DIY tool?
so cool
yes, i made wooden mandrels to help me in making coils....
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Old 23rd November 2011, 10:11 AM   #33
AJT is offline AJT  Philippines
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Quote:
please give me your secret formula?
there is no secret formula, trust me.......it is just plain hard work, but i enjoy it....
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Old 23rd November 2011, 11:02 AM   #34
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Default What about this toroid?

I hope this one is more interesting to discuss
but I still waiting someone to tell me the approximate VA for no 1 & 2?

Anyone can give me new formula for this trafo, please?

few years ago I made it,
it's okay or bad trafo

even the formula to make this trafo, I don't know
Maybe better if any suggestion to testing to know it is good or not
I don't have an AC A-meter
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Last edited by JOHN BALI; 23rd November 2011 at 11:06 AM.
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Old 23rd November 2011, 01:53 PM   #35
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Great thread !

I don't recall this being answered, but how is the equation A = sqrt(W) / K derived ? This has been the one design parameter about transformers that has always eluded me; how does the VA rating correspond to core size.
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Old 23rd November 2011, 08:55 PM   #36
AJT is offline AJT  Philippines
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Quote:
I still waiting someone to tell me the approximate VA for no 1 & 2?
and i am waiting for you to give the core dimensions, core area is you can please....hard to tell from the photos....

i do not give credence to any label on the traffo alone.......
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Old 23rd November 2011, 08:58 PM   #37
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The gross over simplification of A= sqrt(w)/k is simply that: a rough fit for small transformers. Although, interestingly enough, watts = core area in (cm^2)^2 works out for a 50 kva pad mount transformer, a bit on the conservative side though, predicting 40kva.

Last edited by johansen; 23rd November 2011 at 09:27 PM.
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Old 23rd November 2011, 09:02 PM   #38
AJT is offline AJT  Philippines
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Quote:
how does the VA rating correspond to core size
IMHO, temperature rise is one single biggest factor......

for the same size of core, you might spec it at say, 100watts at 50*C temp rise, while another might spec it at 50watts 20*C temp rise....

i always go back to this site for refreshers, powertranschokes
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Old 23rd November 2011, 09:32 PM   #39
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Quote:
Originally Posted by Tony View Post
IMHO, temperature rise is one single biggest factor
It is, and the reason is that volume follows the cube, surface area the square. You have to reduce the power loss, or reduce the current density. At some point, you simply can't make a transformer any bigger, iron loss alone would melt the core. I believe they top out at about 1 KVA per kilogram for near gigawatt capacity.. A 50 kva pad mount transformer is typically 360 VA per kilogram, and 98.5+% efficient. A 1 kva transformer might be 200 va/kilogram, and only 95% efficient, even if you used the same iron.
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Old 23rd November 2011, 09:42 PM   #40
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Quote:
Originally Posted by Tony View Post
IMHO, temperature rise is one single biggest factor......
A low B transformer will stay cool, but also stray fields will be minimal (two coil c-core transformers have already an advantage over EI), and the transformer will be more quiet; all these factors are somehow interrelated.
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