The reply from ERich sums it up well. The explanation of swapping the
primary leads of one transformer will be easier than jumpering the heavy
gauge secondary leads.

The main factor of knowing when the secondaries are phased properly for this
application, is because the secondary conductors will be heavy gauge
conductors, and this could pose a physical parts layout problem
(particularly if you've already chosen an enclosure for your project).
The phasing factor is a result of the direction that the windings are wound
around the core. Since it's undetermined (because the primaries were
existing windings and usually covered), although it's not really important
since you're working with two xfmr cores and you'll be adding your own
secondaries.

The phase can be checked by winding a few turns of any small conductor on
the cores. Two secondary leads from separate xfmrs are connected and two are
left separated. When the test confirms that you've got the leads connected
correctly, you'll want to wind your secondaries in the same direction as the
test windings, and you'll want the four primary windings to retain the same
relationship to being paired together.

If you dont have your secondary windings wound yet..
A low voltage test light will light (6 to 12V) when connected across the
open leads when the windings are not correctly connected or out-of-phase for
the application you want. This is the unwanted maximum current condition
that ERich mentioned.
This lamp test will show how the the xfmrs are phased. You would probably
want your secondary windings to be wound for your convenience, in that the
leads can be attached in parallel to the soldering unit's output cables or
terminals, without any leads needing to be much longer than the other set.

You can bond the xfmr frames to the unit's safety earth ground in the event
of a component failure.

WB
.................

"Eric R Snow" wrote in message
news
Bill,
I know the windings need to be phased. I've never done this but I
gather all that needs to be done is to measure the voltage out. It
should be the same when two are connected in paralell. If less, then
one is out of phase. I don't know any other way to tell if my home
wound windings are connected correctly. I do know that there are phase
dots on some xmfrs that I have on the shelf.
Eric