Author Topic: Understanding Center Tapped Transformers  (Read 3196 times)

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Offline queennikki1972Topic starter

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Understanding Center Tapped Transformers
« on: April 27, 2019, 02:24:52 pm »
I tried to search for a thread on this before posting.

I have a few questions regarding center tap transformers. Very amateur questions..

First,

If you have a center tapped transformer of say 12v-0-12v and is labeled 12v (2.5amp) - 0 - 12v (2.5 amp) and sold as a 5amp transformer 30VA total, does this mean you can acquire max of 24v at 2.5 amps across the two outside wires across the bridge rectifier before the regulation circuits?

Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline madires

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Re: Understanding Center Tapped Transformers
« Reply #1 on: April 27, 2019, 03:04:54 pm »
Such a transformer would deliver (12V + 12V) * 2.5A = 60VA. For 5A you would need a transformer with two separate 12V @ 2.5A windings which you could parallel. Adding a bridge rectifier plus filter cap changes AC into DC and also changes the values. The 24V AC becomes nearly 34V DC (V_RMS * sqr(2)) and the current 1.7A (I_RMS / sqr(2)). These are the theoretical values, the real ones will be lower (voltage drop of diodes, ripple and so on).
 
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Online iMo

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Readers discretion is advised..
 
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Offline mariush

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Re: Understanding Center Tapped Transformers
« Reply #3 on: April 27, 2019, 03:21:34 pm »
 Your 12v - 0 - 12v 2.5A -  can be used as a 24v 2.5A transformer ... you simple leave the center tap pin/wire disconnected, unused.

Some transformers have a center tap which can be separated, to create two separate secondary windings. In this configuration, you can wire the secondary windings in parallel to get double the current, but half the voltage - so you get a transformer that outputs 12v AC at 5A.

If the center tap can not be separated, you can still get higher current but low voltage but not using a bridge rectifier, see below  :

(i'll edit this message further in a few minutes)


 
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Offline queennikki1972Topic starter

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Re: Understanding Center Tapped Transformers
« Reply #4 on: April 27, 2019, 09:36:25 pm »
I understand that it would be 24v at 2.5 from the paragraph above, but I wonder why they advertise it as 5 amp.

https://www.ebay.com/itm/12V-CT-5A-Power-Transformer-6-3V-0-6-3V/321565034079?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline queennikki1972Topic starter

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Re: Understanding Center Tapped Transformers
« Reply #5 on: April 27, 2019, 09:39:54 pm »
Sorry i posted link to a 6.3-0-6.3 by accident
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline ifrenide

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Re: Understanding Center Tapped Transformers
« Reply #6 on: April 27, 2019, 09:51:53 pm »
the only reason they advertise it as 5A to indicate the total current that this transformer draw but its confusing little bit they tell you a truth but not the practical use of this 5A  :-DD
 

Offline mariush

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Re: Understanding Center Tapped Transformers
« Reply #7 on: April 27, 2019, 09:54:44 pm »
Well, look at the picture, you can see the label on the transformer .... the ebay guy probably just went with the text printed on transformer... 6v 5A = 30VA ... simple math.

FYI 25$ for a transformer is not a very good price.
You have distributors like Digikey or Mouser... here's for example Digikey : https://www.digikey.com/products/en/transformers/power-transformers/164

Here's all transformers 20VA or higher, with 6v..9v secondary windings : https://www.digikey.com/short/pz7n5z

A 36VA model is ~11$ plus shipping : https://www.digikey.com/product-detail/en/triad-magnetics/F12-2850-C2/237-1565-ND/3986340

Here's all transformers 20VA or higher, with 10v..15v secondary windings : https://www.digikey.com/short/pz7nr3
Cheapest 30VA model is 10$, and an 80VA model is less than 20$ : https://www.digikey.com/product-detail/en/triad-magnetics/VPS24-3300-B/VPS24-3300-B-ND/4746278


 

Offline queennikki1972Topic starter

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Re: Understanding Center Tapped Transformers
« Reply #8 on: April 27, 2019, 10:28:09 pm »
Thank you..
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 


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