Transformer wiring - Primary has 4 wire ends, secondary 2 ends

Discussion in 'Power Electronics' started by RogueRose, Oct 5, 2016.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    The model is 430-7101(3) and is from an APC UPS and there are 2 of these that run in series - Each has a 4 wire connection on the main board and the terminals on the mainboard look to be in parallel.

    I did a continuity test on the 4 wires and wire 1 & 3 and 2 & 4 signal as a single wire. Wire 2 (black) has a 15A 125v inline fuse and all wires are 16awg.

    Since this is a UPS, IDK which is considered primary as if it is being battery fed, then the larger gauge would be primary and step up the voltage.? But I didn't think DC could be stepped up like this, Could that be why there are 2 sets of wires on the high voltage side?

    I'm trying to find out what the output voltage is of the transformer and wanted to know what wires to use to test 120 AC. I was thinking that using 1 & 2 as + and 3 & 4 as - , but wanted t check if that would be correct (fusing concerned me)

    Actually after thinking about it, I think the 2 sets are for 120 and 240. When 120 is detected connector 2 and 3 are "shorted" to make a longer wire. Does that seem possible?

    transformer.jpg

    transformer2.jpg
     
    Last edited: Oct 5, 2016
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    If it is a transformer there would be different gauge windings.
    Can you see the windings ?
    Can you meashre the resistance of the windings ?

    I once got few of those from a 1.5KVA APC slim type UPS and they turned out to be just inductors....o_O
     
  3. RogueRose

    Thread Starter Member

    Oct 10, 2014
    235
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    The other side has 10awg windings

    I found this video which uses a similar transformer and it was from a similar UPS as this one. He has the 4 connector jumped in some way or it is the live wires connected to the outlet. It looks like he has connected 1 and 4. His transformer is larger than mine it seems.

    I tried hooking up 120 to connector 1 and 3 and it tripped a 15A Breaker immediately. 1 and 3 have continuity and 2 and 4 have continuity. So I thought running power through 1&3 or 2&4 would be the right thing. I'm looking for some other vids or posts of people testing units from these UPS's.

     
  4. tranzz4md

    Member

    Apr 10, 2015
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    Yes the two windings are primary and would be connected either in parallel or series depending upon the input voltage. (parallel for 120v, series for 240, for example).

    I doubt that those two Transformers are connected in series but it is possible. Typically they be connected parallel to each other each performing a different function in the unit. They are connected to the AC input line ahead of any rectifiers.

    If these are older and smaller units one Transformer could be for the input line ahead of the rectifier and the other could be for the output line after the inverter.
     
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  5. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    Thanks for the reply. It is a 2200VA unit and both transformers are identical if that matters.

    I found a schematic for this unit but the board is a 0735 and mine is a 0734 rev 5. They seemed to make many revisions a year...
     
  6. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    I took pics of the board (better pics) and it shows the 2 transformer connectors clearly. They seem to be in parallel and I'm trying to confirm the primary winding's APC_Trans_1.jpg APC_Board_Front.jpg APC_Board_Back.jpg .
     
  7. tranzz4md

    Member

    Apr 10, 2015
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    Well, I can't answer that without an understanding of what you mean by "primary", because the use of that term is pretty relative! Most people mean the higher voltage windings by primary, but some mean the windings connected to the feed side of the circuit-as opposed to the load side.

    Additionally, UPS designs do things with transformers that are very unusual, and I haven't really ever spent the time to work through their schematics to get a clear understanding of some of their games. They'd get rid of transformers if they could beat their inductive characteristics, and as R!F@@ implied, they sometimes use large, wound inductors.

    I thought I might give you some quick help, but let's see what some others have to say.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I have used 650Va APC UPS transformers for countless projects.
    One project was use 4 them for a power amp project. It works to this day but I say the darn thing is heavy. But it does provide plenty of power.

    I cannot help OP.
    He did not provide the resistance measurements I asked for.
    He did not provide a complete transformer picture. I need to see the whole unit.
    Plus it would be easier if OP has a auto transformer to do some tests.
     
  9. RogueRose

    Thread Starter Member

    Oct 10, 2014
    235
    6

    I waited on the resistance measurements because I thought there was something wrong with my meter. I tested on an identical other transformer and the measurements were the same so it seems the meter is correct.

    16awg side:
    White/Black .6 - .7 ohm (initially read 1.3 for a second then would jump between .5 and .8 then settled at .6 - .7 ohm)
    Blue/yellow ~.1 ohm - would bounce between 0 and .1 but reached .2 on initial connection

    10awg side
    White/Black - .1 ohm - stable


    Trans_top.jpg Trans_top2.jpg
     
  10. Rahulk70

    Member

    Dec 16, 2016
    236
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    Hi,
    I know this is an old post but seen quite of a lot of post about UPS transformers here. Thought I will share my experience. I salvaged one from a 700VA UPS. First of all, you can never find the details of these transformers with those useless labels on them, they are usually custom made for the particular manufacturer. Some of the things about UPS transformers:
    1. The LOW voltage side is the one with thicker wires, usually a 2 wire or centre tapped 3 wire.They have lower gauge thick wires for higher current capability.
    2. The HIGH voltage side has thinner windings for lower current.
    If you connect the thicker wire side to mains you blow up the fuse or the transformer.

    Yes, a UPS primary/secondary functions are reversed when it operates in the inverter mode but for the sake of identifying the leads quickly I've considered the transformer as part of battery charging circuit.

    How to determine the primary 120V input wires? There are two ways:

    1.This is the easiest way. Get a cheap 12VAC or 9VAC 500mA transformer and use the 12 or 9VAC to connect to the UPS transformer low voltage side(thicker winding with 3 wires, you can leave the centre wire.You have only two wires BLK/WHITE so its fine). You will get high voltage at the other side. Use a multimeter to measure the voltage across the four wires.Beware this will be higher voltage,70-100V if it's a 120V transformer(I assume your trans is 120V like mine) or 180-200V if it is a 220V transformer.

    2.The second method is to connect the transformer to another UPS outlet. UPS's have an electronic overload protection.You plug in the wrong way you will trip the UPS and save the transformer and you can still figure out. Also, use only a 500VA to 700VA UPS anything above it will damage the transformer by overheating the thick wires and melting the varnish/enamel insulation. Why UPS? because make a mistake on the mains and its BOOM!!!.

    Edit: ATTENTION: Do not PLUG the UPS into the MAINS and then do the second test. It should only be performed with the UPS unplugged from 120V/220V mains and UPS in test mode aka inverter mode or the UPS will be damaged instantly as R!f@@ has mentioned below.
     
    Last edited: Jun 6, 2017
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Check your memory buddy.
    Lower AWG means thicker wires.
    Higher AWG means thinner wires.

    Do not assume a UPS can withstand dead shorts on it's output.
    At times it will trip and at times the UPS itself will fail.

    Connecting mains require experience and care.
    One need to use proper CB.
     
  12. Rahulk70

    Member

    Dec 16, 2016
    236
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    Thanks mate for pointing out that error. I've corrected it. Of course if its one of those cheap Chinese UPS then it might damage the UPS. I tried mine on a 120 VAC 500VA APC BK500 and it worked perfectly fine. Since the lower voltage winding has lower AWG it will draw current like dead short so it will trip the UPS instantly, well unless you hold the test button deliberately(usually the power resistor and the 3 pin regulator IC will heat up and get damaged). But like you said its better to be safe than sorry later. I had got my UPS from a junkyard so it was okay for me. In any case, the first method is the safest.
     
  13. tranzz4md

    Member

    Apr 10, 2015
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    I've heard of others doing the "UPS" method and having good results, and then later on a different UPS smoking it. It's all about current limiting and "inrush" characteristics (when you make a "wrong" connection, or a faulty condition exists). DC testing of AC devices has always been of limited value, but awareness of the differences, and approximations of correct values and offsets/multipliers will help acquire good results.
     
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