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Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

Discussion in 'Power Electronics' started by bushtech, Oct 27, 2017.

  1. bushtech

    bushtech

    888
    139
    Sep 13, 2016
    WTH! Disconnected the secondaries, stuck in a new fuse, switched on and it blew immediately.

    Bridge rectifier?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It can't be the bridge rectifier, because with the secondary disconnected, all there is in the circuit is the transformer.

    I wonder if you have damaged it
     
    bushtech likes this.
  3. Audioguru

    Audioguru

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    Sep 24, 2016
    The transformer secondary or the extra windings around it that power the meter probably has a shorted turn.
    EDIT: Isn't the transformer a toroidal type? Then is its mounting method shorting its core?
     
    bushtech likes this.
  4. bushtech

    bushtech

    888
    139
    Sep 13, 2016
    Still have not found the problem.
    Resistance of the primary winding = 6.2Ω
    Resistance of secondary winding = 0.4Ω
    No continuity between primary and secondary windings
    Toroidal mounted with cable ties so no chance of shorting there.
    No continuity between winding for meter and and any of the transformer leads
     
  5. bushtech

    bushtech

    888
    139
    Sep 13, 2016
    Is there any way I can conclusively test this transformer?
     
  6. Audioguru

    Audioguru

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    Sep 24, 2016
    If the toroid has a piece of metal in it attaching it to something then the metal is a shorted turn around the toroid core.
    If the primary winding, the secondary winding or the winding you added to power your meter has one turn of wire shorted to a turn of wire beside it then the transformer is shorted and will draw a very high current.
    I do not know how you can find where this kind of problem is located.
     
  7. bushtech

    bushtech

    888
    139
    Sep 13, 2016
    Thanks Audioguru
    As I said the transformer is attached to the plastic box with cable ties so no metal anywhere. I am rather dubious that the meter winding is causing it but I suppose I can unwind that lot and retest.

    But I would like to find a way to test the transformer. Can I fire it up and check for continuity between primary and secondary windings? Not sure how continuity test on DMM works.

    Do those resistances of the windings look suspect in any way?
     
  8. Audioguru

    Audioguru

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    Sep 24, 2016
    Continuity between primary and secondary would be when they are shorted together. One ohm-meter probe on the unpowered primary wire and the other ohm-meter probe on the secondary wire and with no continuity then the meter will read infinite Ohms.

    I have never used a toroid transformer and I have never measured the windings resistances of any transformer. Maybe the datasheet for your transformer lists the resistances. Note that you must subtract the resistance of the meter leads.
     
    bushtech likes this.
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The traditional way of checking for a shorted turn is a "ring test".

    This essentially involves connecting a capacitor in parallel with the winding, inserting some energy, and watch it ring.

    The easiest way is to place a charged capacitor across the winding while watching it with an oscilloscope that gets triggered by the initial impulse.

    Then you need to interpret the results. You count the rings (oscillations) until their amplitude decreases below some fraction of the original impulse. The number of rings is proportional to the Q of the tuned circuit.

    A shorted turn drastically reduces the Q of an inductor.

    However, because you may not know what Q your expecting (it won't be very high for a mains transformer) the best thing to do is to compare two identical transformers. The next best thing to do is to add a shorted turn (easy for a toroidal transformer) and see what difference it makes. If it makes a huge difference, then you probably didn't have a shorted turn. If the difference is small, you may have.

    For more information, Google for "ring test inductor" and you'll have an plethora of hits to trawl through.

    Personally, I think your problem IS NOT a shorted turn. After being reminded that you're using a toroidal transformer, I think that you've just been bitten by the dreaded inrush current.

    There are lots of articles on the web. If you google "transformer inrush limiting" you may have enough reading for a lifetime. There is a thread on the eevblog forum that is good.

    My suggestion of a series resistor and a relay shorting it is described here as well as a number of other options.
     
    bushtech likes this.
  10. bushtech

    bushtech

    888
    139
    Sep 13, 2016
    Thank you for a great reply steve.

    Yeah, this power supply's original fuse survived countless turn ons, 2 disastrous shorts and lots of incorrect wiring and wrongly inserted components while attached to a series lamp.

    Yes, come a cross the famous blue ring tester being used often.

    Puzzled that 73's de Edd's thermistor didn't tame the beast.

    Moving forward I'll either use it with series lamp or insert a bigger fuse while all the time keeping an eye on it.
     
  11. bushtech

    bushtech

    888
    139
    Sep 13, 2016
    I'm starting to think that *steve*'s suggestion of a series resistor and a relay might be the way to go. But consulting Dr Google came up with stuff like this: http://sound.whsites.net/project39.htm which is way above my pay grade.Can somebody tell me how to do this (in words of one syllable) or point me to a simple design
    Any advice appreciated
     
  12. Audioguru

    Audioguru

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    Sep 24, 2016
    Everything I have made and my purchased TVs and sound systems do not have fuses.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Check this link.

    A resistor, a capacitor, and a relay will make an effective time delay (power it from your unregulated DC) and pick appropriate resistor(s) for inrush current limiting.

    You need to be careful that turning the power supply on while it is connected to a heavy load doesn't prevent the relay from pulling in (this will likely fry the current limiting resistors).
     
    bushtech likes this.
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Eeek!
     
  15. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir bushtech . . . . .

    I think that the simplest solution with that being a toroidal transformer and a potential very-very short and instantaneous initial surge of up to. 30 amps.
    Wisely you don't want a fast blowing, single wire link fuse , nor even the 3 bead modification which you are using now. (That type of which, I call a medium action fuse.)
    I don't know if that is a full length fuse or one of the "shorties" , and looking back only showed it placed upon a tablet with its ruled lines.
    Just now remembered the MANTECH name . . .
    so look at their bonafide ( spel chek sez "debonair" . . .but I DON'T think so ) time lag /or/ slow blowing fuses that have the internal working element looking like this.

    upload_2018-6-27_9-21-40.png

    Go for either a 1 or 1.6 amp unit and along with that already installed inrush thermistor, I believe that your problems will be solved. This just happens to be a pic of the "shorty" You are a peein' version

    73's de Edd
    .....
     
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  16. m3vuv

    m3vuv

    2
    0
    Sep 8, 2019
    why the hell not build a soft start relay into it,inrush current issue blowing fuses sorted,simple to do as well.
     
  17. m3vuv

    m3vuv

    2
    0
    Sep 8, 2019
    why not use a soft start?
     
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