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I bought 2 center tapped transformers because I need to make 30V 2A center tapped transformer equivalent and I couldn't find anything with a 120V input.

So I got a 18V 2A center tapped transformer and a 12V 2A center tapped transformer.

How can I connect the secondary together so I get a 30V 2A center tapped transformer equivalent?

Mahendra Gunawardena
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kaminsky59
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    Not without breaking apart the windings and un-centertap one of them. – winny Feb 25 '18 at 21:47
  • Would two 15v transformers have given you 30v with a centre tap - why pick two odd ones?? – Solar Mike Feb 25 '18 at 21:50
  • Remember to derate VA rating 30% if you plan on a bridge cap load so you may want 90VA or consider a COTS SMPS, when you buy your next power source. – Tony Stewart EE75 Feb 25 '18 at 21:58
  • You COULD do it if either of those transformers had a split secondary (2 isolated 0-12V windings) instead of centre tapped. –  Feb 25 '18 at 21:59
  • https://www.digikey.ca/products/en/transformers/power-transformers/164?k=&pkeyword=&pv1617=115&FV=9300451%2C930045b%2C930046d%2C9300478%2C930047b%2C930047d%2C930049e%2C93004b5%2C93004c7%2C93004d1%2C93004db%2C93004e8%2C93004f5%2C9300547%2C9300573%2C9300654%2C93006bf%2Cffe000a4%2C19440073%2C19440037&quantity=0&ColumnSort=0&page=1&stock=1&pageSize=25 – Tony Stewart EE75 Feb 25 '18 at 22:01
  • Now that you know the difficulties and are stuck with these two transformers for now, maybe we should ask: "For what purpose do you need the 30 V @ 2 A, center-tapped transformer?" – jonk Feb 25 '18 at 22:10
  • I am working on building this 19v dual rail power supply. http://www.siliconchip.com.au/Issue/2010/June – kaminsky59 Feb 25 '18 at 22:38

2 Answers2

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Basically you can't. If you connect the secondaries of your transformers in series, you will get 30V across them but the common connection will not be a center tap since one side will be at 18V and the other at 12V. If you got 2 of the 18V transformers, you would get a center tapped 36V transformer by connecting the secondaries in series. Two of the 12v transformers connected in series will give you a 24V center tapped transformer. You really need 2 15V transformers and they don't have to be center tapped. When you connect them in series, the common point becomes the center tap of the 30V transformer.

Barry
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  • Related to the question, in my case i have 2 SMPS with 24V 5AMP , what wire connections are needed in order to get 24-0-24 5AMP at output ? Do they have to be in parallel ? if so then what will be the center tap point ? – Vikrant Mar 18 '20 at 18:53
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It's easy. Give both a bridge rectifier - they give you a DC output. Connect them in series.

Michel Keijzers
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John Tube
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