Electronics > Beginners

Understanding Center Tapped Transformers

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queennikki1972:
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?

madires:
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).

iMo:
https://www.changpuak.ch/electronics/power_supply_design.php

mariush:
 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)


queennikki1972:
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

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