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Old 16th January 2011, 03:50 AM   #1
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Default Is it possible to get 15v from 2x15v transformer?

Hi guys as above

I need 0-15v. However tranformer off the shelf are 15v-ct-15v

Is it possible to get the 15v out while using the full rating?

Can i connect the two 15v and take the 0v from the ct?

Thanks
Erwin
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Old 16th January 2011, 04:22 AM   #2
tomchr is offline tomchr  United States
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Ground the center tap and take 15 V from one of the two ends. Terminate the other end (i.e. cover the end with some heat shrink tubing or some electrical tape). If the secondary is rated for 100 mA you can get 100 mA out of it when wired that way.

Another thing you can do is to use a different rectifier. I assume you'll rectify the output of the transformer with a diode bridge. That will result in about 18~20 V DC. If you instead connect the center tap to ground and connect each end of the secondary to the anode of a diode you get full-wave rectification as well. The cathodes of the diodes go to the reservoir cap. Like this (from Wikipedia):
Click the image to open in full size.

~Tom
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Old 16th January 2011, 05:27 AM   #3
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Quote:
Originally Posted by tomchr View Post
Ground the center tap and take 15 V from one of the two ends. Terminate the other end (i.e. cover the end with some heat shrink tubing or some electrical tape). If the secondary is rated for 100 mA you can get 100 mA out of it when wired that way.

Another thing you can do is to use a different rectifier. I assume you'll rectify the output of the transformer with a diode bridge. That will result in about 18~20 V DC. If you instead connect the center tap to ground and connect each end of the secondary to the anode of a diode you get full-wave rectification as well. The cathodes of the diodes go to the reservoir cap. Like this (from Wikipedia):
Click the image to open in full size.

~Tom
thanks tom for the reply.

i need to connected it to the ready made psu board. hence option 2 is not viable.

so option 1 is way to go.. so only taking from one of the tap while leaving the other 15 volt would allow me to get the full rating of the transformer? that is nice to know.

as i was suggested by lokal seller to combine the two 15v taps and take the ground from CT.

just want to confirm

thanks
erwin
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Old 17th January 2011, 10:32 AM   #4
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by milen007 View Post
as i was suggested by lokal seller to combine the two 15v taps and take the ground from CT.
No !

connecting the two 15Vac ends is the same as connecting the secondaries out of phase.
That should blow the mains fuse almost instantly.

Use a bulb tester to check your work. Otherwise you may injure yourself or damage your equipment.

The only way to use both 15Vac tappings is the use of the two diode rectifier as in post2. It is only 2diodes. What's difficult about that?
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Old 17th January 2011, 11:27 AM   #5
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Erwin,

Many toroidal power supply transformers are supplied with two separate secondary windings, i.e. 0-15V/0-15V.
When so, there is no single CT, and you could wire the two secondary windings parallel to get the full power of the transformer.
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Old 18th January 2011, 04:31 AM   #6
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ahh got it.. thanks guys. just talk to the seller again. he said to cut the CT and wire it as a 2x15v. but guess i just order a toroidal with 2x15v

hi andrewT. do you mind show me the link on how to bulb test our work?
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Old 18th January 2011, 09:47 AM   #7
AndrewT is offline AndrewT  Scotland
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insert bulb tester in the search, or dim bulb test, or bulb ballast, google the same
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Old 18th January 2011, 11:07 AM   #8
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Hi Erwin,

just to clarify things: Does your transformer has any kind of wireing schematic diagram on it? And if so, does it look like picture 1 or more like picture 2?

Martin
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File Type: jpg Center Tapped.jpg (5.2 KB, 101 views)
File Type: jpg Dual Secondary.jpg (5.5 KB, 105 views)
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