heavy duty bench supply

Discussion in 'General Electronics Chat' started by electronis whiz, Dec 24, 2012.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    i was resently given a big 2200VA UPS. ended up was like 10+ yrs old and conroler board was fried. got a pair of tronsformers from it thatst weigh about 20 lbs the i am reversing them so that instead of lov voltage to 120 i want 120 to 12. the low voltage side has 2 10AWG wires. i conected to a bridge rectifier and filter cap for DC, i'm considering seting up in paralell for more A, but like the 2nd on a seprate switch. is there anything to be woried about just letting the other one sit with no primary power to it, other than a bit extra heat, and the 120V outputput that it would make. also what do you think i can get out of just 1 transformer in terms of A?
    also seen some bench supplys with sires/ paralel selection switches, may consider doing that, but don't know how they do that. tryed to figure out for anothe project and couldn't fiugre out.
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    I assume you want to connect these transformers together to get 120VAc in and 12vAc out,
    http://www.google.co.uk/imgres?q=tr...w=184&start=0&ndsp=27&ved=1t:429,r:3,s:0,i:97

    if that is the case then you can either parallel them together but the secondary side will have to be connected IN-PHASE or you can use separate bridge rectifiers, then parallel the outputs. As for the current you will have to measure the load with an ammeter.
     
    Last edited: Dec 24, 2012
  3. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Hello Electronis whiz ! Re: My listing in " flea market " for ' large transformers' - page 2
    I have several of these, culled from Minuteman UPS units, and yes, they make one grand base for a hi-amp 24v power supply with those # 8 leads.
    Cursory hookup shows that using what would be the primary, the large leads put up 32v unrectified, ergo the 24v estimate. I even have some 140 Amp pigtail rectifiers to play with......

    IF I am interpreting the coils rightly -- Normally, the #8 leads, are backfed by the inverter driven off the battery, to feed the outlets on the UPS. One thing I'm not exactly sure of, is will the " primary " which is normally the UPS inverted output, handle the load drawn by the rectified #8's. Since these things are not cheap to buy or ship anywhere --- 30 pounds a pop, I do not want to waste them---

    Any info you have discovered about them we could compare notes on would be super.
     
    Last edited: Dec 24, 2012
  4. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
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    intersting thing on mine my system was a 48V system with the pair of low voltage leads in series, but upon testing they put out more like 14V. i thought about trying an amp meter, but my DMM only goes up to 2 A. but some old anolog ones may work. if their not in phase what will happen? planing on putting in 2 switches one main and another to activate 1 or bothe transformers. i put the biggest rectifier i had in it. a big square aprox 2X 2 in and screwed down to the metal case to heatsink it. should that be ok for oth or should i look for a biger one?
     
  5. PackratKing

    Well-Known Member

    Jul 13, 2008
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    called for help with some questions along the line of what you are asking, and "Don Q" sent me this. :

    There's a little confusion of primary/secondary input/output, but here is some general info that you may have to invert/modify if I misunderstood your intent.

    If it has a single primary, and it is not already center-tapped, it will not be possible to 're-tie' the coils to give a center-tapped coil on what the transformer labels the primary, at any voltage.

    **** Start here ***

    It is possible to 'back-drive' transformers, i.e. using the secondary as the primary and vice-versa. The secondaries having equal ohms does not necessarily mean that they have the same number of turns. You can determine this by simply running it and measuring voltages.

    I would strongly suggest using some lower AC voltage while testing, just for the safety aspect of it. Using a 12VAC wall-wort type power supply (or some equally low current AC supply) will show the same ratios, but at a survivable 'oops' potential. This won't be able to drive any load, so don't apply one except for a multimeter/scope yet.

    If the secondary windings have the same output voltage, you should then either go by the phasing info available for the xformer, or determine it yourself with a scope, or by series connecting separate windings. If they are in phase, the AC voltage will add, if they are out of phase the voltages will subtract. This is the point where the 12VAC comes in handy. Depending on the 'grounding between coils', connecting in series may create a short. This is manageable with a low-current 12 VAC input, but frighting and dangerous connected directly to the line.

    There are a number of possible combinations available depending on what you find, the easiest would be with two 120V coils in series on the secondary side, backdriving what used to be the non-center-tapped primary but is now used as the output. This is for 240VAC input, 120VAC output.

    The third secondary could be used as another output, depending again on that grounding thing. Figure it out at 12VAC, then try it with a fused 120V. Best would be to parallel, in-phase, with the other 'output' to allow twice the current, at half the voltage of the input (watts in=watts out).

    Then, regardless of how you wind up wired, don't go above the current rating of any of the individual windings. Ground all cases, fuse all inputs/outputs, keep your hands in your pockets, and all the other usual precautions when working with line voltages.
     
  6. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
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    i have done tests on these as folows. 1 did ohm test worked showed 0 ohms. also verifyed between the all the leads and the frame with only ohms showing for a winding. so asked a frind about it and he put it on a transformer tester. then pluged it in and got 14-18V out. the transformer has 2 large 8-10# leads that were in sires betwwen them. on the other side there are smaller like 16-14# leads. i folowed the wires to how they were set up on the PCB through relays, fuses, etc to the line in. put the plug on those leads we pluged it in tested voltage off large lead. it also had another winding i tested that with same input setup and got the same voltage as the large wires, but just taped them off.
     
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