Differences between transformers

[b00ker]

I'm trying to put together a linear power supply for a TPA3255 board. I ordered a transformer from a company who shall remain nameless. It's 500VA and 34V transformer. They have two at these specs. One simply has 2x outputs at 7.4A (according to their specs). The other one has 2x 34V at 5.8A, 2x 12V at 2A, and 2x 18V at 2A.

I wanted the former (I only want the 34V out), they sent me the latter.

I sent them a message and they replied saying that both transformers are the same Spec, that I should just cut off the extra output wires on the one I received.

According to their specs, the latter transformer can output fewer amps at 34V. Is this assuming some kind of load on the lower voltage outputs? Should I just bite the bullet and use the one they sent me, or should I make them take this one back and get the one I intended to order.

Thanks a bunch

 

[tomelex]

I'm trying to put together a linear power supply for a TPA3255 board. I ordered a transformer from a company who shall remain nameless. It's 500VA and 34V transformer. They have two at these specs. One simply has 2x outputs at 7.4A (according to their specs). The other one has 2x 34V at 5.8A, 2x 12V at 2A, and 2x 18V at 2A.

I wanted the former (I only want the 34V out), they sent me the latter.

I sent them a message and they replied saying that both transformers are the same Spec, that I should just cut off the extra output wires on the one I received.

According to their specs, the latter transformer can output fewer amps at 34V. Is this assuming some kind of load on the lower voltage outputs? Should I just bite the bullet and use the one they sent me, or should I make them take this one back and get the one I intended to order.

Thanks a bunch

If you sent me the wrong transformer, then send me the correct one, own up to your mistake. End of story IMO.

 

[solderdude]

The power rating of a transformer is given at their nominal load.

400W @ 34 + 24 @12V + 72W @18V =496W
the other is 503W

As you won't be drawing power from the 12 and 18V windings all 'magnetic' power will be available for the 34V windings.
So 496 W @ 34V so 2x 7.3A.

 

[Raindog123]

There is also such a thing as transformer linearity related to primary-secondary coil alignment. (Long time ago, I had to manually wind transformers for high accuracy dA/dV measurements in a physics experiment using modulation technique.)

But in the author‘s case without additional details or measurement, it is hard to claim that one transformer is superior to the other. And, as we‘re talking about a power - ultimately a rectified DC power - transformer and not a coupling one, it should not matter much.

 

[b00ker]

This is all great, thanks everyone. I think I have the info I need to figure out what to do now.