Serie connect two 115v transformers for 230v mains??

[mg73]

I have a PSU for bipolar +-24v and it has two internal Triad 115V transformers(not two windings on same transformer).
The transformers are parallell connected internal to the 115v mains plug.

Would it work to internal serie connect the transformer and use it for 230v mains?

 

[sodderboy]

Is this a commercial PSU, DIY kit, or pile o' collected bits?
Mike

 

[mg73]

Photos

 

[JohnRoberts]

I have a PSU for bipolar +-24v and it has two internal Triad 115V transformers(not two windings on same transformer).
The transformers are parallell connected internal to the 115v mains plug.

Would it work to internal serie connect the transformer and use it for 230v mains?

Yes and no.... the primary voltage would be OK, but another consideration is that 230V mains are generally 50Hz. If the 115VAC windings are designed for 60Hz they may be marginal.

[edit- maybe try it (carefully) and see if it works /edit]

JR

 

[mg73]

Flickinger

 

[mg73]

Yes and no.... the primary voltage would be OK, but another consideration is that 230V mains are generally 50Hz. If the 115VAC windings are designed for 60Hz they may be marginal.

[edit- maybe try it (carefully) and see if it works /edit]

JR

Thanks JR,
According to Triad's datasheet the transformer can handle 50/60Hz

I tried it with a Variac(variable AC volt unit) slowly increasing up to 230v and it worked fine
A bit uneven on the transformers 111 on one and 119 on the other
but no problem dialing in +-24v on each side with the trimpots.
But haven't tried it with load yet.

But not sure i it's any dangerous l scenarios could occur
and if that would damage anything.
For ex if one side of the secondary's load gets lost
could voltage exceed 24v on the other side then
or if one transformer gets shorted on the primary side

 

[ccaudle]

But haven't tried it with load yet.

The load is reflected back to the transformer input, and the effective impedance of the transformer primaries will determine the balance of how the 230V is divided between the two primaries. You might get something like a higher load on the output of the second transformer causes an increase in voltage on the output of the first transformer.

 

[cyrano]

Years ago, the local army surplus had loads of 110V transformers. I used those in series several times. As long as they have equal power ratings and the draw on them is more or less the same, it's not a problem.

The only time the smoke came out, was on a DIY symmetrical DC supply, cause I often used only the positive side. While testing a DC motor, both transformers went up in smoke.

 

[abbey road d enfer]

I have a PSU for bipolar +-24v and it has two internal Triad 115V transformers(not two windings on same transformer).
The transformers are parallell connected internal to the 115v mains plug.

Would it work to internal serie connect the transformer and use it for 230v mains?

That would be more or less correct if the current draw is identical on both polarities.
I would be somewhat concerned with start-up. If one side starts earlier than the other, voltage could be wrongly shared.

 

[Matt Syson]

Ensuring current/power sharing of the AC side (and hence the voltages seen on each primary) of these transformers will be near impossible for many of the reasons mentioned above. The 50/60Hz difference is mostly an issue when cheapskate American (60Hz) gear is used on a 50Hz supply. A fair number of American bits of gear buzz mechanically and prospectively more 'ripple' on the DC supply because there is not enough iron in the core (and reservoir capacitors may be undervalued when used at 50Hz). Functioning is different to functioning 'perfectly'.

 

[abbey road d enfer]

Ensuring current/power sharing of the AC side (and hence the voltages seen on each primary) of these transformers will be near impossible for many of the reasons mentioned above.

So posts #6 and #8 are fictions?

 

[Hubbub]

If you are going to use two transformers with primaries in series and want to avoid the magic smoke you should 1) make sure the transformers are built identical, and 2) connect the secondaries in parallel, phased properly. If you skip #1 or #2 then there is NO guarantee of either transformer having a proper voltage on the primary or secondary. Your regulator may go up in smoke, your transformer may go up in smoke, or your equipment may go up in smoke - taking something really expensive with it.

 

[JohnRoberts]

Here is a little DIY high voltage transformer shenanigans. I needed to make some insulation leakage measurements at 500V but did not have an easy supply. I did have a pile of 120/20 VAC transformers. I wired one transformer in the forward direction. Then I connected several 20V secondaries all in parallel with the first. The now floating 120V primaries got wired in series, 4 of them made the expected 480VAC.... Kids don't try this at home.

Even when doing bench shenanigans I used a 1/4A fuse.

JR

 

[radardoug]

If you are going to use two transformers with primaries in series and want to avoid the magic smoke you should 1) make sure the transformers are built identical, and 2) connect the secondaries in parallel, phased properly. If you skip #1 or #2 then there is NO guarantee of either transformer having a proper voltage on the primary or secondary. Your regulator may go up in smoke, your transformer may go up in smoke, or your equipment may go up in smoke - taking something really expensive with it.

LIKE HE SAID!!!! Do it right or dont do it.

 

[abbey road d enfer]

Of course, making the xfmrs talk to each other is safer than relying on equality.

 

[abbey road d enfer]

View attachment 110506

Here is a little DIY high voltage transformer shenanigans. I needed to make some insulation leakage measurements at 500V but did not have an easy supply. I did have a pile of 120/20 VAC transformers. I wired one transformer in the forward direction. Then I connected several 20V secondaries all in parallel with the first. The now floating 120V primaries got wired in series, 4 of them made the expected 480VAC.... Kids don't try this at home.

Even when doing bench shenanigans I used a 1/4A fuse.

JR

Of course, making the xfmrs talk to each other is safer than relying on equality.