By Chris Zizzo


From Port Lines Hobbies

How does one wire two or three AF transformers so they are in phase with each other?

It will be helpful (although somewhat erroneous) to think of phasing as you might consider battery polarity, you know, + to + and - to - . In actuality, AC power switches between + and - 60 times a second, and phasing is simply a way to get your transformers to do it in unison rather than opposite each other.

First, phase your transformers two at a time. Then add a third, if desired.

Wire the base posts of two transformers together. Plug the units into a multi-outlet power strip and plug that into a wall outlet. Ignore, for the time being, the 7-15 volt variable posts. Hook a wire up to ONE of the 15 volt fixed voltage posts. Gently touch the free end of that wire to the 15 volt fixed voltage post on the other transformer. There should be little or no spark. If there is a bright blue spark (which may trip the onboard circuit breakers), then unplug EITHER transformer (but not both) from the power strip, and rotate the plug. Restore the transformers to operation by resetting any tripped breakers. Then repeat the procedure of lightly touching the 15 volt post of one transformer with a wire connected to the corresponding post on the other transformer. This time, there should be no spark. These two transformers are now phased.

If adding a third transformer, it is most important that you consider the first two units to be unchangeable. If a plug must be rotated, rotate the plug of only the third unit, so as to not change the phase relationship of the first two. In fact, the reason for the multi-outlet power strip is that you always maintain the correct phase relationships by keeping all the transformers plugged together, in phase. You can unplug the power strip from the wall, but it will not change the relative phase established between the multiple units.

Wire the base post of the third unit to the base post of either of the other two transformers, so that all three are now wired together. Take the free end of that 15 volt fixed post test lead and touch the fixed post of the new unit. If there is not much spark, you're all set. If there is a big spark, then rotate the power plug of the new unit, re-set the breakers and try again. Now, a wire touched to any two fixed voltage posts should be nearly spark free.

You can also use a multi-meter. In phase, fixed post to fixed post should be a volt or less. Out of phase, it should read as high as 30 volts.

In practical use, you would insulate track blocks with fiber pins on the 7-15 volt variable side, while keeping all your base post rails well connected. The phased transformers will keep the basepost jumper installed. This will allow smooth transitions from block to block with no reverse unit glitches.


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