XPost: sci.electronics.design, sci.electronics.equipment, sci.el   
   ctronics.repair   
   XPost: rec.crafts.metalworking, rec.woodworking   
   From: dhky@shaw.ca   
      
   On 11/02/2014 11:40 AM, 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   
   > which­­not 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.   
   >   
   -----------   
   It appears that you have 4 windings- 2 heavy and 2 lighter ones. For a   
   simple buck or boost transformer V +/dv you only need two windings so it   
   appears that the transformer can be used for 120V input or 240V input as   
   can the transformer whose diagram you sent.   
   The HV input winding(s) will have thinner conductors.   
   You can get a reasonable approximation of turns rations by measuring   
   resistances -roughly  proportional to ths square of the turns.You have 4   
   coils H1-H2 H3-H4 L1-L2 and L3-l4   
   Take one of the HV coils- label it H1-H2 and energize it at a low   
   voltage to start (always err on the low side) with H1 at the neutral   
   end. Measure the voltage across  all   coils  This will establish turns   
   ratios.  Don't label numerically but simply with  regard to voltage   
      
   The other thing is to establish polarity.   
   Now take one of the other coils and connect one end of it to the H2 or   
   high  terminal of the first coil (please de-energize while doing this).   
   Measure the total voltage from neutral to the free end- if it is more   
   than the H1-H2 applied voltage- it is boosting so  free end can be lab   
   with an even number H4, L2 or L4 and give the other end the   
   corresponding odd number.  If the voltage is less, it is bucking so give   
   it an odd number. Do this with each  of the  other coils -so  you will   
   end up with another measure of turns ratio but, more importantly, you   
   will have their polarity established with even numbers as the same   
   polarity and the  coils all numbered. Using this scheme, your diagram   
   would be in  a buck mode.   
   Now you can figure out the combinations available to you.   
   there are quite a few.   
      
      
      
   --   
   Don Kelly   
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   --- SoupGate-Win32 v1.05   
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