[AMPS] How to find the Correct Phase for 240V Transformer Primary Windings ???

[Phil (VA3UX)]

Fairly easy Kurt.  Here's the procedure :

1.  With your multimeter in the Resistance mode, find the leads associated
with each winding.  Label the leads for one winding 'A' and 'B', and the
leads for the other winding 'C' and 'D'.

2. Connect leads 'B' and 'C'  together.

2. Apply an AC voltage to ONE of the windings; lets say you use the 'A' -
'B' winding. Use 120 volts or less.

3. Set your multimeter to measure AC volts. Use a range for 250 volts or
higher.
 Connect one lead of the multimeter  to lead 'A' .  We'll arbitrarily call
this the "Start" lead for that winding.

4. Touch the other lead of the multimeter to lead 'D' .

5. If the multimeter reads 240 volts (or twice whatever voltage you applied
to winding 'A' - 'B'), then lead 'C' is actually the "Start" lead of
winding 'C' - 'D'.  Lead 'D' is then the "Finish" lead for this winding.

6. If the multimeter reads Zero volts, then lead 'D' is the "Start" lead
for winding 'C' - 'D'.

7. You could then re-label your leads as "Start" and "Finish" for each
winding.  Or, you can keep the A-B  C-D labels, just make sure you label
them so that 'A' is the Start for one winding and 'C' is the Start for the
other winding.  'B' and 'D' are both Finish leads.

For series operation of the windings (230 - 240 V), the "Finish" of one
winding is connected to the "Start" of the other winding.  In the scheme
above, that would be 'B' and 'C' connected together (but NOT 'A' and 'D').
The two remaining leads - 'A' ( Start ) and 'D' (Finish) - would be
connected to the power supply (mains).

For parallel operation (115 - 120 volts), both Starts are connected
together, and both Finishes are connected together.

Make sure the leads for the secondary winding are totally open.  We don't
want accidental shorts during the test.

Be very careful since you're working with voltage that can be lethal.  I
prefer to power the windings through a dinky little 12V or 24V transformer
for the test.  It provides isolation from the mains and provides some
current limiting if I make a mistake (which means the flash isn't quite as
bright as it otherwise would be).

That's it.

Phil


At 10:59 PM 8/17/2000 EDT, you wrote:
>
>Hi Fellas, A question for you High Voltage Transformer Guru's. I have an 
>unlabeled transformer. I have found the primary windings. This transformer 
>can be powered by 120 or 240 volts. Heres the question. How can you tell the 
>phase of the windings in order to properly set up for 240 operation. I'm not 
>sure if this will help determine it but the pig tails of the windings are 
>Brown/Black and the other is Blue/Yellow. As always any help would be
greatly 
>appreciated...  Thanks, Kurt, K3KL...
>
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