Identifying buck-boost transformer windings?

Question

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

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.

etpm · Accepted Answer

I have the wiring diagrams in .pdf for Square D buck/boost xmfrs. The X wires are the heavy wires and the H wires the thin wires. X1 and X2 are the ends of one winding. X2 and X3 the ends of another winding. The other windings are similar. Anyway, if you send me an email I'll send you the .pdf of the wiring manual. Then you will be able to figure out how to wire the thing. It should be easy enough, just measure the output in one random configuration and you will be able to tell what's what by looking at the manual. Eric

DaveC · Answer

Have a wiring diag:   How to wire it isn't the question. Which wires are H1, H2, X1, X2, etc. is  the question.  Series light bulb or Variac (will use 120 mains for testing as that is the  only Variac I have...) seems the answer.  Remaining question: are H1/2 and H3/4 primary windings interchangeable? X1/2  and X3/4 windings interchangeable?  Thanks.

Spehro Pefhany · Answer

Say you have 8 wires. If you measure the resistance between any one wire and any of the remaining 7 wires, what do you get? There are 28 unique combinations (8 * 7/2):

Eg.

Wire to Wire R (Ohms) ?? A B A C A D A E A F A G A H B C B D B E B F B G B H C D C E C F C G C H D E D F D G D H E F E G E H F G F H G H

Best regards, Spehro Pefhany

Identifying buck-boost transformer windings?

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