Salmon Egg wrote:

In article
,
DaveC wrote:

Imagine you are asked to install a used buck-boost transformer. Imagine you
could normally do this in a few minutes. Except if the leads were cut short
such that identifying characters on the leads' insulation were missing.

Identifying 2 leads belonging to any one winding is straightforward ohm meter
work. Maybe use of a ESR meter might help separate the X windings from the H
windings?. But identifying which specific winding is which and which end is
which--not so straightforward. For me.

How would you go about identifying the windings? Maybe use a Variac to input
voltage to each of the windings then measure the output of the others? What
outputs should I expect at, for example, the H3/H4 winding with a voltage on
H1/H2 winding? How to identify backward connection of a winding?

Are the two H windings identical? The two X windings?

Suggestions welcome.

This is a 208 - 230 (ie, 12 & 24 v buck-boost voltage) single-phase
autotransformer in N. America.

Thanks.

I am intrigued by this post and the replies. The post has little useful
information and the replies are based on assumption that that may have
little connection to reality. From the description, I have no idea if
there really is an auto transformer, completely separate windings, or a
combination of both. Also I have no idea what a description "H3/H4
winding" means. I refuse to guess. Try to understand this communication
is in writing and not telepathic.

1. An ohmmeter can separate one set of connected windings from other
such sets. If there are taps, you might even find the ends of the
windings and and the order of the taps.

2. Put all these winding sets in series.

3. Using your Variac, energize one winding (without saturating).

4. From voltage measurements you should be able to find the turn ratios
amongst the various windings.

5. You should also be able to locate which ends of a winding are in
phase or out of phase with the ends of your excited winding.

In the future, realize that good communication requires good grammar and
little ambiguity.


There is no ambiguity. A typical datasheet will tell you that 'X' is a
high voltage lead, and that 'H' is a low voltage lead.

If you'd ever installed one you would know that they have two
primaries and two secondaries, all four isolated. For 120, you parallel
the primaries in phase. The secondaries are connected in series with the
load. The phase affects the addition to or subtraction from the line
voltage. It isn't rocket science. I recently installed one on a pipe
bender at a factory, right after the company had moved to a larger
building.

That machine had two problems. It was built for 240 volts, and they
had 208. The other problem was that the so called industrial electrician
they hired wired it for 120 V because he was too damned lazy to go back
to the shop and get the right breaker. A boost transformer and the right
breaker had it working better than it had at their old location, where
it had been on a 208 volt circuit.


For your transformer, all you need is an ohm meter to identify each
winding, and an AC voltmeter to figure out the phasing of each winding.


The logical steps a


1: Identify the pairs of the thin leads with an ohm meter. These are
the primaries.

2: Identify the pairs of the thick leads with an Ohm meter. These are
the Secondaries.

(BTW, I would put a cable tie around each pair of leads, near the
transformer to keep track of each pair in case you need to reuse it in
the suture.)

3: For 208, connect the two sets of primary wires in series. If you
have 12 volts on the outputs, they are in phase. If not, reverse one set
of the primary leads.

4: Connect a pair of the secondary leads in series. If you get 24
volts, you can use it for 24 volts. If you get zero, connect the
remaining two leads together will give you 12 volts. Just keep in mind
that you only get half the current at 24 volts.


Page 93 of this PDF shows the primaries wired for 120 or 240 and the
secondaries in series or parallel to give 12 or 24 volts boost or buck

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja& ved=0CFwQFjAP&url=http%3A%2F%2Fwww.hammondpowersol utions.com%2Ffiles%2FHPS_Catalog_BuckBoost_Section 2.pdf&ei=nr_8Uri1A_fNsQT11YAY&usg=AFQjCNEyTy77_co5 ZMOQii2jkEUDw8W1Cw&sig2=-VF-Fyg1XsdHDckcm9EIjw

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