Odd result when phasing transformers: ZW-L and Postwar ZW

 Did you measure "hot to hot" on both transformers?.

It's  looks  like  one of transformers is out of phase now. Can't explain why.

I would  check  the nuertal connections

If you  put the two  positive together you double  the voltage. That  explains why light  is very  bright. 

Yes, hot to hot as described by Mike R. and Marty E.  If they are out of phase, why wasn't it corrected when I switched the plug 180 degrees on the PW ZW?  I'm stumped.

You're supposed to connect the bulb between the two A terminals with the U terminals connected together but not to the bulb lead. One lead on A of the ZW-L and one lead on the A of the ZW.

What this does if the transformers are phased alike is the bulb rides up and down with the ac voltage the same on each side of the bulb. So it will be dim or out. If the transformers were not in phase, then the one side of the bulb would be at positive half cycle and the other side of the bulb would be at negative half cycle, so it would be very bright.

Oh, I see I confused the issue.  I actually tested it two different ways.  Hot-to-hot as described by Marty E. and Hot to common as described by Mike R.  Same outcome.

The ZW-L needs to have a significant load - I would recommend a 2-3 amp test load on both transformers and try it again, and use an analog VOM. The ZW-L is a switching power supply, altering the duration and shape of the waveform instead of the amplitude.

Using an oscilloscope would be the easy way to phase the two, another easy way would be to use a VOM/meter(analog for simplicity), using your same method, but with both transformers at full throttle - 37-39 volts NOT in phase, 0-5 volts IN phase.

It's both the same.  

Try this:  First, set each ZW A-U voltage at 16V (measured with your meter).  Then connect the U terminals from each ZW together.  Now measure A to A with your meter.  If it is close to 32 volts you are out of phase.  Close to 0 volts and you are good.  

The reason I said set both to 16V first (and measure it) is to eliminate the possibility of one of the A-U outputs being bad.  You could do the same thing on the B-U, C-U or D-U terminals as well.  Just make sure what ever pair you use that the voltages are set the same on both ZW's.

Tony

ToledoEd posted:

 Set the A handle on both to 16v, plugged them in, turned on the power strip and connected one yard light lead to the A terminal on the ZW-L  and the other lead to the ZW's common.

 

Your second connection should have been to the ZW's A post NOT the common. Then if in phase the bulb would have been dim or off.

Steve

Mikes presentation of phasing transformers is confusing I think. He does a thing with three transformers showing they are all in phase by lighting a bulb while all the transformers are connected in parallel. Since they are in phase, they don't fault and you can connect a bulb between A of the first one to common and light the bulb. If they were not in phase, I don't know what would happen since two of them are electronically protected to fault to zero volts while the small third transformer is probably protected inside by a fuse or a breaker. Not helpful, I think.

The correct phasing test is what Marty said and what others said on this thread. Connect the commons (U terminals) together and a bulb across A to A. With the transformers set to the same voltage, if the bulb lights brightly, they are not in phase, if the bulb is dim or out, they are in phase. Simple.

As recently as last week, there was a discussion about phasing two transformers. There is a discussion, on average, about this every 3 months or so. Checking the archives will allow you to see the best answers. Here is what I wrote on the subject a few days ago:

"Connect the two posts that you intend to use as a common, with a piece of wire. For instance, a "U" on each transformer.

Set the outputs of each transformer at the same voltage.  Use the meter leads to do this. The color doesn't matter.  Go, for example, from the A to the U post, first on one transformer, then the other, to check their output voltages. Get them as close as possible to the same voltage.  Use, for instance, 12 Volts.

Set the meter scale at 0-50 Volts A.C. or some similar range. Use one lead on one "A" post and the other lead on the other "A" post.   You are trying to determine if the difference between the output voltages is near zero (transformers in phase) or if it is the sum of the two voltages you set in step 1, (24 Volts.)

If you get zero, you're all set. If you get the sum, reverse one plug in the wall. Mark the plugs to allow repeated success, or plug them permanently into a plug strip, secure them with tape, and use the male end of the plug strip in the wall.

There have been hundreds of messages, YouTubes and other lessons posted on this subject.  Try the archives of this forum."

cjack posted:

You're supposed to connect the bulb between the two A terminals with the U terminals connected together but not to the bulb lead. One lead on A of the ZW-L and one lead on the A of the ZW.

What this does if the transformers are phased alike is the bulb rides up and down with the ac voltage the same on each side of the bulb. So it will be dim or out. If the transformers were not in phase, then the one side of the bulb would be at positive half cycle and the other side of the bulb would be at negative half cycle, so it would be very bright.

I attached the PWZW U terminal to the ZW-L U terminal. Then I attached the leads of a bug to the A terminal of each.  The light was bright irrespective of the position of PWZW plug.  I also touched the leads of a voltmeter to the A terminals. Voltage was exactly as it was set on each transformer, 14v or so.  I hope I didn't confuse the issue.

Thanks for helping.

ADCX Rob posted:

The ZW-L needs to have a significant load - I would recommend a 2-3 amp test load on both transformers and try it again, and use an analog VOM. The ZW-L is a switching power supply, altering the duration and shape of the waveform instead of the amplitude.

Using an oscilloscope would be the easy way to phase the two, another easy way would be to use a VOM/meter(analog for simplicity), using your same method, but with both transformers at full throttle - 37-39 volts NOT in phase, 0-5 volts IN phase.

Thanks, I'll try that.  Sorry about the bold, don't mean to shout but my cursor got captured in the quote..  Argh.