Dual output transformer vs centre tapped transformer?

[Robbie010]

Hi all,

Can someone please tell me whether a dual output transformer is the same as a centre tapped transformer?

I have project amplifier that currently has a 300VA 24-0-24 centre tapped transformer per channel and I was looking to swap them out for modern toroidal transformers. Within my limited budget I have found one on eBay but it is listed as 2x 24v output not centre tapped??

Thanks.

[Paul Rose]

Not strictly same, but should be just as good.  You can make a center tap out of dual output, but not the other way around.

Connect the 2 secondaries in series, use the connection point as the center tap.  You have to get the phase right.   If you get it right, you will get 48 across the two outputs that are not connected.  Otherwise you will get almost nothing.

[Brumby]

Two separate secondaries allows for much greater flexibility.  If you are ever faced with a decision to purchase a transformer with dual secondaries or a centre-tapped secondary (with the same voltage and current specifications) - my advice is to always get the one with dual secondaries.  This allows you to run with (a) two isolated circuits (b) paralleled for greater current or (c) in series for higher voltage with centre-tap as a bonus.

With a centre-tap secondary, the options (a) and (b) are not possible.

To use dual secondaries in a centre-tap configuration:

Connect the 2 secondaries in series, use the connection point as the center tap.  You have to get the phase right.   If you get it right, you will get 48 across the two outputs that are not connected.  Otherwise you will get almost nothing.

[GeoffreyF]

Depends on how they are wound.   Toroidal transformers are not especially "modern".  They are also different.   If you are replacing something in an existing circuit, I suggest that you replace it with something pretty close to the same *OR* understand that circuit very deeply so that you know what you are doing.

Different transformers are different in a lot of different ways.  You could do further damage to the system that you have if you happen to choose a part that is different in the wrong way.

[Richard Crowley]

A center-tapped is just a single winding with a tap in the middle. It gives you no option how you can use it.

OTOH, a dual winding with the proper two wires connected together performs exactly the same as a center-tapped winding.  BUT it also gives you the option of connecting the windings in parallel for "half" the voltage, but double the current.

Disclaimer: This applies to "ordinary" cases at low frequencies (power mains, audio, etc.)  When you start getting into esoteric applications, RF, etc. it is a different discussion where stray capacitance starts to have an effect.

Replacing a center-tapped transformer with a dual winding transformer of equivalent voltage and current should be a slam-dunk.  Don't over-think it.

[Jwillis]

Although highly unlikely but not improbable. the two secondaries may not be wired as expected. So don't freak out if you get 0 or near 0 volts instead of the  expected 24 or 48 volts.
It just may be that one secondary is out of phase with the other. Just change the way you've wired it on the secondary to correct the issue.