[Amps] Transformers in parallel

[craxd]

Well,

If they are the exact transformer, same number of turns in both primary 
and secondary, and the same amount of iron, they can be ran 
parallel-parallel or series-parallel. If one is off just a small amount 
from the other, one will draw more current than the other. I've seen 
them hooked to the rectifiers two different ways. One, both transformers 
secondaries are connected in parallel and then hooked to the rectifier. 
The other, two separate rectifier supplies made and up both connected at 
the filters through resistors.

This last one proposes some problems however. This makes a mis match on 
each set of rectifiers. Most of the time, each rectifier set will have 
its own filter. Then off each filter, a "balancing resistor" is used. 
These the two resistors are connected together off of each supply. The 
resistors tend to level out or balance any current differences between 
the two. This method is done a lot in other power circuits both in tubes 
and semis.

The first way, with both secondary windings connected in parallel, has 
any mismatch behind the rectifiers. This keeps the rectifiers and 
filters from having different currents in them. What then happens is 
that one transformer will heat up more than the other (in the above 
circuit, it will too, but the whole supply circuit with it). If it's a 
small mismatch, this dissipation wont be very much.

One last note. The windings must be connected in phase with one another. 
This means the start of one winding connected to the start of another, 
and both ends of the windings connected together. If they're connected 
out of phase, with two equal voltage coils, one will cancel the other 
the same as a short. Some of the leads are color coded for this but most 
are not. Theres some simple tests to determine the phasing in several texts.

All in all, it's much easier just to connect both secondaries parallel, 
and have one rectifier/filter assembly.

Will Matney


Hello

Could the primary and secondary windings of two identical transformers be wired in parallel to double the current rating?

Or would it be better to rectify and filter seperately and then wire both in parallel.

Looking to make a 2600V 3 amp DC supply with two identical 1.5 amp transformers.

Thanks

KC4MNE