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Old 21st January 2005, 04:08 PM   #1
tmblack is offline tmblack  United Kingdom
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Default Winding Your Own Transformers

Has anyone tried to wind their own power transformers?
I'm considering a 120V to 50VCT transfomer @5A.
I have some EI cores of M4 steel, 1.5" center tougue and 5" long.

Anyone know the proper method to do this?

Regards,

Tom
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Old 21st January 2005, 04:48 PM   #2
sss is offline sss  Israel
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few tips
first u gotta find a core that can handle that power (500VA) and got enough space for the windings
most of the time u can use a core taken from 500VA (or more)transformer
also its much easier if u allready got the primmary coil (suited for 120V)
if u got all of the above , winding the secondaries wount be a problem
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Old 21st January 2005, 05:53 PM   #3
tmblack is offline tmblack  United Kingdom
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I already have the core as mentioned above. Not sure how to calculate the maximum VA rating for it but it but I can stack up the laminations(it does have to be square).

I just threw a number for the current but 5Ax50V should only be 250VA, not much for its size.

Tom
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Old 21st January 2005, 06:19 PM   #4
sss is offline sss  Israel
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50V @5A ct = 500VA(each secondary 250VA)
or maybe u meam 25-0-25
an oversized core is not so good, u will use longer wires=higher output resistance
if u got no primary coil u gotta calculate the number of turns for 120V operation , i dont remember the formula for this
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Old 21st January 2005, 11:59 PM   #5
Stocker is offline Stocker  United States
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Somebody wants you to do this... I found this earlier today...
Roll your own power transformers

Do let us know how it turns out!
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Old 22nd January 2005, 01:42 AM   #6
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here;s an article from a magazine which went bust about a decade ago:
http://www.tech-diy.com/rewinding_transformers.htm
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Old 22nd January 2005, 02:35 AM   #7
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*Sch3mat1c wonders where Geek is

Lesse, http://geek.scorpiorising.ca/windingtransformers.html seems to be the one.

Your core sounds about right. You want to use a core somewhat oversized so you don't run out of room when you're almost done with the windup. Too large a core is just a waste of good core material.

Don't worry about resistance. A good transformer will barely get warm. For 5A, you'll want around 16-18AWG copper wire.

Tim
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Old 22nd January 2005, 02:53 AM   #8
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Quote:
Originally posted by sss
50V @5A ct = 500VA(each secondary 250VA)
or maybe u meam 25-0-25
CT always means the full voltage winding is split, so 25-0-25 would be accurate. However, given power factor of a capacitor input filter, a 500VA (i.e., 10A RMS) rating may be advisable.

Quote:
if u got no primary coil u gotta calculate the number of turns for 120V operation , i dont remember the formula for this
A book I have gives it as E = F * H * N * A * 4.44 x 10^-8, with E in volts, F in Hz, H in "lines of flux per square inch" (1 tesla ~= 60,000 lines; a good value is 50-80k), N is turns and A in square inches (cross section of the center of the core, which the turns are wrapped around). With some algebra you can find whichever you need.

Looks like you'll need about 300-350 turns for the primary.

Tim
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Old 22nd January 2005, 06:53 AM   #9
tmblack is offline tmblack  United Kingdom
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Gentlemen,

thank you for the assistance. I'll try my best to get something done.

Tom
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Old 10th April 2010, 08:02 AM   #10
AJT is offline AJT  Philippines
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Quote:
Originally Posted by tmblack View Post
Has anyone tried to wind their own power transformers?
I'm considering a 120V to 50VCT transfomer @5A.
I have some EI cores of M4 steel, 1.5" center tougue and 5" long.

Anyone know the proper method to do this?

Regards,

Tom
50v @5amps is 250Va, but primary VA needs to be around 350va.....looks like a 1.5 inch center leg stacked to 2.5 inches height is good.

primary turns of about 280 of ga #19 using grain oriented silicon steel, more if not using goss...

secondary turns of 120 #14 split into 2 coils of 60 turns each...wired in series to get the center tap.

you have to find out your coil buildup and adjust turns or wire size to fit into the window of your EI cores.

if you can get hold of a bobbin, then scramble winding is easier to do... you only need to worry about primary and secondary coil insulations.....
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