Connecting a transformer

[madan1]

Good day.
Just a quick question - I have the following toroidal transformer:
PRI: 2x 0-115 Blue-Grey Violet-black
SEC: 12v Red-Black
SEC: 12v Yellow-Orange

How should I wire it to get 230 on Primary and 24-0-24 on SEC if it is even possible?

Will 220 to single PRI winding and then Red-black_yellow-Orange do the work, or probably 220 on both PRI in parallel?
Both SEC are rated to 6.7A, so I guess if I you double the V on PRI, the rated amperage should be divided by 2?
Also, does it matter which ends of the wirings of the SEC are used for zero reference? Is there a difference whether it will be Red-Black_Yellow-Orange, Black-Red_yellow-Orange, etc.?
Thanks in advance!

[sam_sam_sam]

There should be a dot on each winding to show you how to wire it

It is one dot on one primary winding a no dot on the second winding hook together for 220 and the same thing on the secondary winding as well for 24 volts

If you were doing 115 in parallel you would put the two dots together and the two that do not have dots together same thing for the secondary side for 12 volts with more current capacity

The dot represent the direction of the winding and phase of the transformer

[momaka]

You CANNOT put 230V through a winding intended for 110/115/120V AC, because it will overheat the winding (eventually) if not cause the transformer to saturate right away.
Put the two PRIMARY side windings in SERIES to get one whole primary winding for 220/230/240V.
However, careful attention must be paid to how these two are placed in series. If you don't put them in series the correct way, the two windings will cancel each other out and you get a near short-circuit on the primary, which = . To avoid doing that, use a 100W incandescent light bulb in series with the transformer's primary (after wiring the two primary winding in series.) If the bulb lights up and stays lit, you've wired them incorrectly. If the bulb doesn't light up, check the voltage at one of the 12V secondary windings - it should be correct at 12V AC.

That said, unfortunately, you cannot get 24-0-24 from two 12V windings. You can get either 12-0-12 or 0-24 with the two secondary windings in series.

Is this for an amplifier power circuit, by the way? If yes, you can still get reasonably close to the equivalent of a 24-0-24 winding if you wire the rectifier circuit as a voltage doubler.

[sam_sam_sam]

You CANNOT put 230V through a winding intended for 110/115/120V AC, because it will overheat the winding (eventually) if not cause the transformer to saturate right away.
Put the two PRIMARY side windings in SERIES to get one whole primary winding for 220/230/240V.
However, careful attention must be paid to how these two are placed in series. If you don't put them in series the correct way, the two windings will cancel each other out and you get a near short-circuit on the primary, which = . To avoid doing that, use a 100W incandescent light bulb in series with the transformer's primary (after wiring the two primary winding in series.) If the bulb lights up and stays lit, you've wired them incorrectly. If the bulb doesn't light up, check the voltage at one of the 12V secondary windings - it should be correct at 12V AC.

That said, unfortunately, you cannot get 24-0-24 from two 12V windings. You can get either 12-0-12 or 0-24 with the two secondary windings in series.

Is this for an amplifier power circuit, by the way? If yes, you can still get reasonably close to the equivalent of a 24-0-24 winding if you wire the rectifier circuit as a voltage doubler.

Thank you for pointing this out about using an incandescent light bulb to check weather or not you have the correct phasing for dual primary and secondary winding

[redwire]

madan1, dig for the transformer datasheet, it makes things easier. If you can't get it, then the only risk is the primary (phasing). If it is wrong you will burn the primary windings.
The common connection is either Grey to Violet, or Grey to Black. Secondary doesn't matter either you get 24V or 0V if they are cancelling each other.

You can use a (primary) current-limiter like a light bulb, or what I do is use a signal generator and put in say 5V sine wave 1kHz into a winding and measure ACV on the others.

[lotas]

Connection example...

[madan1]

Thanks for the replies.
Of course all tests will be done with a current limiter (tungsten filament bulb).

You CANNOT put 230V through a winding intended for 110/115/120V AC, because it will overheat the winding (eventually) if not cause the transformer to saturate right away.

What about if I connect the two 110 wirings in parallel (with both windings in the correct direction)? Shouldn't that spread the load across both windings?

use a 100W incandescent light bulb in series with the transformer's primary (after wiring the two primary winding in series.) If the bulb lights up and stays lit, you've wired them incorrectly. If the bulb doesn't light up, check the voltage at one of the 12V secondary windings - it should be correct at 12V AC.

Isn't 100 watts too much? By the way, any idea what is the idle current of a toroidal transformer.. I mean with disconnected secondary side?

Is this for an amplifier power circuit, by the way? If yes, you can still get reasonably close to the equivalent of a 24-0-24 winding if you wire the rectifier circuit as a voltage doubler.

Some day, maybe.. At the moment I need 15+VAC ( >+/-17.5Vdc) to test a sound mixer and this transformer is available. Thank you for pointing out the voltage doubler, definitely will check it out.

madan1, dig for the transformer datasheet, it makes things easier. If you can't get it, then the only risk is the primary (phasing). If it is wrong you will burn the primary windings.
The common connection is either Grey to Violet, or Grey to Black.

Well, given my experience with finding any datasheets about transformers (usually smps ones) I'm really surprised there is at least something about that one - https://sg.rs-online.com/web/p/toroi...ormers/2575130 Still, there is nothing about phasing the primary or the secondary. The closest thing to schematic is a visualization of the windings, but I have no idea if this is just for visualization purposes or indeed shows how the windings were placed on the core. From what I've seen, the winding machine uses a double wire so that both primaries/secondaries have the same characteristics. Physically the beginning of coil_pri_1 is on the same place on the core as the beginning of coil_pri_2, but on the datasheet schematics it more looks like the primary is a single wire, which was cut in the middle.

There should be a dot on each winding to show you how to wire it

It is one dot on one primary winding a no dot on the second winding hook together for 220 and the same thing on the secondary winding as well for 24 volts

If you were doing 115 in parallel you would put the two dots together and the two that do not have dots together same thing for the secondary side for 12 volts with more current capacity

The dot represent the direction of the winding and phase of the transformer

Unfortunately, there are no dots.. neither on the wires, nor on the transformer.





P.S. OK, got a second look at the datasheet, I guess on the primary side "110" means LIVE and 0 is neutral.
So phased parallel - Live_1----Live_2 and Neutral_1----Neutral_2 and phased serial - Live_1-----Neutral_2.

[momaka]

What about if I connect the two 110 wirings in parallel (with both windings in the correct direction)? Shouldn't that spread the load across both windings?

In case of putting both 110V windings in parallel: yes, each primary winding will then handle about half of the total load on the output. However, with the 110V windings in parallel and connected to 220V AC line, each 110V winding will still see the full 220V AC line across it... which is not good.

Windings are meant only for AC up to their stated voltage (and at worst case, up to +15% max usually). That's because each winding has a certain impedance under 50/60 Hz - i.e. an "AC resistance", in simpler words. When you raise the AC voltage to 2x its nominal rated value, the dissipation of the winding may increase by up to 4 times its nominal value (i.e. if the transformer is consuming only 10W @ 110V/115V AC connected to its 110V windings, then connecting 220V AC may increase that dissipation to 40 Watts, causing the core and/or wire to overheat.) Also with twice the voltage on the winding, this will increase the magnetic flux within the core... and if the winding tries to push the core flux too far, the core might experience "saturation", causing a collapse in the impedance of the primary winding(s), making them appear like a short-circuit (and thus quickly melt or blow up the fuse.)

So those are the reasons the voltage should not be increased past the rated voltage (too much or for too long.)

Isn't 100 watts too much?

Usually, no, though it does depend a little on the transformer size.
If it's a "puny" transformer under 10-15 VA, you can size down the bulb to 40-60 Watts. But for anything larger, 100W would be my "start" bulb... and more for larger transformers.
An average-sized audio amp transformer tends to consume between 8 to 15 Watts of power with nothing connected on the output. So to make sure the output voltages don't drop too much, the idea is to go with a series bulb Wattage that is at least 10x this "no-load" power draw.

By the way, any idea what is the idle current of a toroidal transformer.. I mean with disconnected secondary side?

Depends on the size of the core... but probably in the ballpark mentioned above, or maybe a bit less if it's better-made one with more and larger copper for the windings.

Some day, maybe.. At the moment I need 15+VAC ( >+/-17.5Vdc) to test a sound mixer and this transformer is available. Thank you for pointing out the voltage doubler, definitely will check it out.

It's very simple, this voltage doubler: with the output windings of the transformer connected in series (for 0-12-24V AC), connect the "0" to the common +/- point of the two caps in the power supply (usually this would be the circuit's GROUND). Then, connect the "24" pin to one or both of the AC legs of the bridge rectifier for that circuit's power supply. On the positive cycle of the wave, you will be getting rectified 24V AC (about 33.5V DC) going to the "upper" cap. And on the negative cycle of the AC wave, you'll be getting rectified 24V AC (about -33.5V DC) going to the "lower" cap. Not sure if that will be too much for your circuit, but just letting you know ahead of time so you can check the voltage rating of your capacitors before trying this out. I did the same for a subwoofer I was fixing and it worked "fine" (minus the fact that the output transistors driving the sub were too small and thus heating up quite a bit under heavy output... thus I ended up replacing my voltage-doubling transformer with 2x 20V laptop adapters wired in series to get +/-20V... but that's a story for another day/topic.)