Power Supply configuration

Discussion in 'The Projects Forum' started by peter_morley, Mar 31, 2011.

  1. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    I made a crude a schematic below of what I have done so far. I'm not 100% sure about the transformer pins but anyways it has two leads for the primary coil. The primary inputs being positive and negative current. The secondary coil has 4 outputs, 2 red lines and 2 green lines. I assumed the red lines are the output current of the transformer and the green lines as ground. Well the problem is with this set up my transformer and rectifier get hot. Not sure what I'm doing wrong. please let me know if i am setting it up incorrectly.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Hi Peter,
    Well, you connected two of the same colors together, so that's basically doubling the current but cutting the voltage in half.

    However, you connected both the reds to the AC input of the bridge which is OK, but you connected the two greens to the negative side of the bridge. This means that during each 1/2 cycle, one of the lower two diodes in the bridge is shorting from a green to a red.

    Have a look at this:

    [​IMG]

    I have a red and a green connected together in the middle, but they are not connected to the bridge. I've also added a 1,000uF filter cap. This should give you the most output voltage your transformer and bridge is capable of for light loads.

    Note the way I have the bridge oriented is different than your schematic. I simply prefer to have all of the cathodes "pointing" towards the right, as that will be the + output. Yours is actually more correct, as the + is on the top and - on the bottom.
     
  3. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    I have it setup the way I believe you intended me to set it up without the capacitor. Now as you said the current did drop by about a half and the voltage pretty much stayed the same. But now its heating up really quickly so I feel like something is still wrong.
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Please do not try it like that again: the way you have connected it is not safe, because you have shorted out one of the secondary windings.

    This will result in the transformer taking a very large current. You can expect it to burn out very quickly this way - it may even catch fire.

    Look more carefully at SgtWookie's schematic - can't you see the difference?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Peter,
    You'll need to use your multimeter set to Ohms to figure out which of the secondary side wires are connected to each other.

    You have two red wires, and two green wires. At this point, I am not certain if two reds are a winding and two greens are the other winding, or if there is one red and one green per winding.

    You must NOT have power connected to the transformer while you are measuring the secondary windings using the Ohms scale.

    Make certain to re-set your meter to AC volts after you are done measuring the windings. Otherwise, you may accidentally damage the meter or blow the meter's fuse if you attempt to measure voltage with it set to Ohms.
     
  6. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    I looked at it again and I'm not quite sure how else to connect red and green together in any other way. Should I connect my two reds together and my two greens and then hook it up that way...but I think that would just give me twice the current. Is that the only problem? Does everything else look alright like the way my rectifier is hooked up.

    I tested for ohms and got no resistance on all of them (while unplugged). What am I looking for I thought coils had inductance?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Disconnect the transformer secondary wires (reds and greens) from the bridge and each other.
    Label the red and green wires using pieces of masking tape, like:
    Red-1
    Red-2
    Grn-1
    Grn-2

    Then set the meter to measure AC volts; 20v or 50v range, plug in the primary side to power, and measure and RECORD the voltages between:
    1) Red1 and Red2
    2) Red1 and Grn1
    3) Red1 and Grn2
    4) Red2 and Grn1
    5) Red2 and Grn2
    6) Grn1 and Grn2
    That is all of the possible combinations of connections.
    Once you have taken the voltage measurements, let us know what you read.
     
    Last edited: Mar 31, 2011
  8. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    I'm not getting any voltage drop for the 6 pairs I tested. Does this mean that they are just sources of alternating current? So I'm assuming that green is not ground. I tried to figure out which red and green couples are paired but I think it doesn't matter because one is sending a positive current the other negative (polarity change). When taking the voltage drops from each line R1,R2,G1,G2 to primary ground I got an ac voltage drop of around 13 for each one. Does this information help?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    You don't measure any voltage across any combination of the red and green wires?

    What is the manufacturer name and part number of the transformer?
    Did you get a datasheet or information sheet with it?
     
  10. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    Its from a guitar amplifier and the identification numbers read like this
    S L M E
    070-60002-100-0
    HK57H-124 C
    I tried finding this on the internet and came up with nothing.
     
  11. peter_morley

    Thread Starter Member

    Mar 12, 2011
    179
    0
    Under my latest assumption (my assumptions are usually awful) of red and green being supply current I hooked up R1 and G2 to the AC rectifier terminals. Then hooked my red multimeter lead to + and then I hooked up my black multimeter lead and wall outlet ground (primary) to the - terminal on the rectifier. I measured in DC voltage a constant 5 volts. Diode has a voltage drop about 1 V i think so maybe 6V out of secondary. I measure 0 current though which doesn't make sense. Both rectifier and transformer are completely cool no overheating. Another thing to note is that after I turn off my switch I still have 0.4 voltage drop across the + and - terminals of rectifier. If I unplug the power chord from the wall the voltage goes back to 0. So my transformer is drawing power even though the DPST is off?
     
    Last edited: Mar 31, 2011
  12. SgtWookie

    Expert

    Jul 17, 2007
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    I found the part number in a UL certification listing. Link:
    http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073754382&sequence=1
    Text:
    Output 15 watts or more or 42.4 volts (peak) or more. Transformer, Cat. Nos. <snip> HK57H-102B, -103, -104, -108 thru -124,

    Manufacturer:
    DAR PLUS ELECTRONIC CO LTD E123107
    19 ALLEY 21, LANE 20 DASHING RD
    LUCHU HSIANG, TAOYUAN HSIEN 338 TAIWAN

    Manufacturer's website:
    http://www.darplus.com.cn/english/light.htm
    There is an E-mail link at the bottom of the page for technical support.
    Your part number is HK57H-124 C.

    You may very well have burned up some windings operating the transformer when it was shorted by the incorrectly wired bridge rectifier.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Well, with no capacitor in there, all you're reading is VERY rippled DC.
    The rectifier bridge won't have much of a drop across the diodes until there is a load. Then it's 0.7v to 1.2v or so per diode depending on the load current and bridge current rating; so you'd have 1.4v to 2.4v drop across the bridge.

    Utoh. Did you try to measure current directly, with no load? That's a good way to fry your meter, or blow the fuse.

    Sounds like your DPST switch is partially shorting. You should get a replacement.
     
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