Transformer Question

Discussion in 'General Electronics Chat' started by Overclocked2300, Jun 30, 2005.

  1. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    I have recently bought a transformer. The out puts are 12.1V @9A, 12.9V@2A, 12.9V@3.2A. My question is, can I connect all the outputs in parallel and get 12V out@14 A?

    Or would the 12.9 and 12.1V outputs fight each other? How would I know where the positive of the transformer is? (you know the dot shown in circuits)

    http://members.fesgaming.com/kaiba/images/transformer.jpg
     
  2. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1

    hi

    you can't connect the 12.1 to the 12.9. the 12.9s can be, however you must check the 12.9v output if they are really equal. if there is some variance in the output voltage, the output of higher value will carry the most load by trying to compensate for the difference. assuming that you will be drawing at least 80% current capacity the coil with the higher voltage output will hotter than the lower voltage value. this would cause premature failure of the hotter coil.

    as to your query where the positive is, there's none. have attach a schem on how it's connected.
     
  3. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    hmmm crap...so then both will need to go to seperate filters....well I have 6 28,000uf Caps in parallel, and 5 5,500uF Caps in parallel. I could split them up and use 3 28,000uf caps..and 2 5,500uf caps for one side and the same for the other. I would still get good regulation..but its going to a voltage regulator after that anyway. But another problem is that I need the outputs to be adjusted at the same time. I Could always load down the 12.9V to 12.1 and use a dual ganged pot so that they both give the same output.

    Wait, if All I need to do is drop .8V or even .7..cant I use a diode in place of R3? I'll take measurements tommrow since it is late.
     
  4. n9xv

    Senior Member

    Jan 18, 2005
    329
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    The dot indicates phasing.
     
  5. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    Ya I wanted to know where that is..Or it doesnt matter?

    EDIT: Voltages Have been Confirmed.

    These were taken under NO LOAD

    12.1V reads 12.9V
    12.9V Reads 13.6V
     
  6. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    ok..this is Odd I went and remeasured those voltages...and they vary. Line voltage is 112.5V rms. I get outputs any where from 12.95 to 13.04V on the 12.1V line, and anywhere from 13.55v to 13.88V on the 12.9V line...What gives? All voltages are without rectification or regulation and filtering. Ive tested it with a load (1k) and the voltages dont move for squat! Im guessing I will have to rectifiy the voltages and filter them?

    EDIT: I hooked up a rectifer, and some filter Caps. The caps take a long time to charge up. They dont even reach 12V. I thought in linear powersupplys they take almost no time charging up. I decreased the filter caps down to 1 5,500uF Cap. It takes about 5 seconds for it to reach 1V. As anyone experienced these problems?
     
  7. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi,

    based on your test measurement of the 12.1vac you would have theoritical bridge rectified output of 18.3v (unloaded). as to the 12.9vac it would have 19.6v. again all these outputs are based on your mainline measurement of 112v. if your line goes up to 120v the secondary will of course also go up.

    if you are going to regulate the output use a adjustable high current regulators so you can change the output voltage whatever level you want.

    it does not take that long for a cap to fully charge. your caps could be defective.

    then the claim on the transformer of +/-3% variance is not true.
     
  8. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    On post #5 those measurements were taken without rectification.

    How would I tell if the caps are defective? Or how would I test? Is it because I dont have a load across them?

    EDIT: Thanks mozikluv, that cap was dead..or I had the leads wrong..haha. If I could give u rep I would for that! Im going to go though and test the others out. Hopefully I'll have enough caps for some good regulation. As said in my other posts, I need atleast 10,000uF.
     
  9. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
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    Well I'll be a sonovagun...The big caps charge slowly...buuut I found that one of the smaller caps charge the same way. So out of curiosity, I let it charge up to 16.67V..and discharged it quickly with a screwdriver. The next Time I charged it It charged perfectly Fine.

    I did the same technique with one of the bigger caps. Works the same way except the one I tried it on was charged at 15.75 volts and had to charge up to 16.67V

    Maybe they are just old and the substance needs to re align itself or something.
     
  10. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    here's a simple guide for capacitance, for every ampere you'll need 2,500uf, so for your transfor you need 22,500uf. this would prevent your output from sagging once you start drawing large amount of current.

    if it can't fully charge, then you have a current leaking caps. the ESR is already high, so it won't endure once you start loading it with high current draw.

    an ESR meter can check your caps if it still reliable.

    moz
     
  11. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
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    Ok..another problem. I measure around 14.5V (after rectification) and when I hook a cap up I get 16.7V, but it increases up to 17V. I thought there could be something wrong with my voltmeter because sometimes it displays nothing at all except values. It usualy displays auto range...etc..
     
  12. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1

    variation in your reading at the secondary is the reflection of the variation of your mains. variations on the rectified & filtered output will vary between +/-10% - 15%. you must always consider this factor to arrive at your maximum output voltage. so if your secondary rated output is 12.9vac, at 15% max. variance that would be 14.8vac and the rectified & filtered output will be in the range of 20.9vdc maximum. for the cap voltage at a ratio of 1.5:1 that would be 35v. that will be your minimum cap voltage rating.

    moz
     
  13. vel

    New Member

    Apr 4, 2008
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    in 100 watts inverter which transformer was suitable(ie readly available transformer eg;12-0-12 3amp,230v)
     
  14. recca02

    Senior Member

    Apr 2, 2007
    1,211
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    Even if the voltages were to be same: for same voltages and frequency AFAIK the transformers are loaded equally..thus if three X'er are connected in parallel u'll need 14/3A capacity for each.

    There is perhaps a way out of this(not sure though-i'll need some brushing up), I think adding external resistance of specific values to each transformer might work.

    Resistance values will have to be calculated based on the current you want the transformer to handle which depends on its individual ratings..
     
  15. Audioguru

    New Member

    Dec 20, 2007
    9,411
    895
    12V times 3A (36W) alternates in each half of the center-tapped low voltage winding.
    The inverter uses about 20W to heat itself.
    Then the output power is only 16W when the little transformer is at its max power rating.

    You need a transformer rated at 120VA for a 100W inverter's output.
     
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