ASK: Determining transformer's windings phase

[Jwillis]

Did some searching and found this method. Now you could apply this method if you have a Known second step down transformer of  240VAC- 24 VAC.This way we can keep the voltages low yet still induce a field to the unknown transformer.
Step 1--Mark the lines on first coil of unknown transformer primary H1 and H2 and H3 and H4 on second primary coil.
 
Step2--  Hook up 24VAC to H1 and H2 you should read around 24V On H3 and H4.

We are going to use additive or subtractive reasoning to determine polarity of second coil in relation to first coil.

Step3 Connect H3 to H2  and apply 24VAC to H1 and  (H2 + H3) measure voltage between H1 and H4.If measurement is additive (48VAC) the coil  is in phase. If it measure is subtractive (0 VAC) then the coils are out of phase .

This method can also be used to determine the polarity of secondary coils in relation to the primary

Although this video Is for determining secondary polarity it can be used to determine primary as well
Just induce a lower voltage AC voltage that is managable.



I tested this method with a 120Vac to 28 Vac transformer  to test a 120/240 Vac  to 15 volt Vac transformer and it does indeed work.

So all you need is a DMM and a known step down transformer.

[BravoV]

Haha, I was holding back on suggesting something like that!  He'd better make sure those clips are really high integrity, otherwise he's going to be searching his remote location for a mA fuse or Aluminium foil / copper nail 

P.S. A really clean turn-off would be advisable under those circumstances too.

Yep, he usually did the hard turn off at panel for such ad-hoc & ghetto measurement on AC motors.


Don't worry about the fuse replacement, he has this poster framed and hanged at his office ... 

[BravoV]

Hi BravoV

[1] Connect the primary windings any way that you like.

[2] Connect an incandescent bulb (40W to 100W) between the pair of primary windings and connect the mains across the bulb and the primary windings in series.

[3] Note the brightness of the bulb

[4] Reverse the connection of the primary windings and repeat [2] above.

[5] Note the brightness of the bulb.

The primary connections that gives the dimmest bulb are the correct connections for 230V.

Thanks, that is exactly the planned steps.

[Ian.M]

Yes the bulb method is the simplest reliable one, provided you can identify the primaries.   Also one should always check the bulb before and after testing.

Otherwise, if you aren't sure which are primaries, you need to inject  current limited low voltage  AC, and measure voltages, then connect selected windings in series and determine whether the voltages add or subtract to check phasing.  Jwillis suggested this method back in reply #25  above, but IMHO 24V is  too high a test voltage as many transformers have secondaries that are nominally 12V or even lower, so if you apply 24V to such a secondary, you risk saturation and even insulation breakdown of the primary + the as-yet unidentified primary is a HV hazard.    IMHO 6V to 8V RMS is a good range for the test voltage source.   Depending on its max output level, your bench signal generator may even be suitable, otherwise get a bell transformer, or an old heavy low voltage unregulated switchable output voltage wallwart you can crack open and mod for AC output and a 15R 5W resistor to put in series to limit the current.

Potted and toroidial transformers  with HV secondaries and no data are a PITA - it can be very difficult to determine which is the primary, and if you get it wrong, you may only have basic insulation between your choice of primary and some of the secondaries.  Carefully measuring capacitance between winding pairs can help determine their proximity, and thus provide some estimate of the likely insulation between them.

[basinstreetdesign]

Has anybody ever had this situation with the dual primaries wired in series but out of phase?  I have and the result is non-climactic.  With all secondaries open, if the primaries are wired out of phase their magnetic fields are in opposition and cancel within the core.  All secondaries then show next to zero voltage.  Except for magnetizing current, the turn-on transient is minimal.  Swapping the leads on one primary brings it right.  Testing this requires nothing more than a meter.

You've contradicted yourself there -- you're applying flux (voltage at frequency) to the sum primary windings; if the field in the core is forced to zero, it can only be that all windings will appear short circuited under that condition!

Since zero minus zero equals zero, the anti-series primaries will see no back EMF, and full mains current will flow (likely limited by the resistance and leakage of that winding, more than the mains supply itself).

(As it happens, this condition does not force the field to zero; secondary voltage is independent of primary connection when the primary is anti-series, and vice versa.  Simply, the amp-turns cancel out, making that winding be a lump of wire wrapped around the core, but otherwise an open circuit to the field.)

If you did in fact have this and nothing happened, then something else was wrong, like the primary was wired correctly but the secondary was opposite (+Vsec - Vsec = 0), or the fuse opened, or the circuit wasn't closed after all.  FYI.
Tim

OK, better late than never, I guess.  My profuse apologies for screwing this up.  I was trying to remember a time almost 4 decades ago when this happened.  What must have happened was that the primaries were good, and in parallel, but I had 2 secondaries in series with nothing coming out and must have had them in anti-phase.  No fuse went and there was no smoke/fire.

As for my second comment about using some of the low voltage secondaries wired in series, that was true.

Anyway, sorry about that (he said, bowing and scraping)...

[T3sl4co1l]

Four decades, you can be forgiven for remembering anything at all

Tim