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Power supply help wanted with bridge rectifier.

Discussion in 'Power Electronics' started by jvdbossc, Dec 1, 2016.

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  1. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    I bought an old zetagi power supply some time ago. It is rated 30 amps 1 minute on and one minute off at 13.xx volt.

    It made a buss noise for a while and then the bridge rectifier died shortly after FB2502 bridge.

    I googled it, it is 25 amps max and cannot deliver 30 amps for one minute.

    I put meters in it voltage, ac amps, and some fans to cool it and I replaced it with bridge gbpc5010. (silver ones chinese 1$)

    Today I wanted to do a field strength meter tests and pulled 30 amps out of the AC side. Even not after a minute of taking that it smoked with a loud bang and then a few smaller bangs. I opened the case and the only thing that was really hot was the didoe bridge gbpc5010 and I could smell diode smell, so its gone.

    There are no small condensators over the bridge as you see in many designs. (103)

    I know it was only pulling 30 amps at the AC side. Bit puzzled what should I put in there?

    At the DC side it was delivering about 16 amps at 14 Volt to my transmitter..

    There is also another protection circuit with a tyristor but it was cool, so it did not activate. The tyristor is only activated at +15V and there are some filters not to make it jump active to early.

    The bridge rectifier is screwed to the main cool block and with that it holds a pcb with paralell 8x4700uf. From there it goes to another pcb wich drive the good old 4x2n3055 wich share the cool block as well.
     
    Last edited: Dec 1, 2016
  2. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    The diode block was screwed tight with new paste.
     
  3. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    Here are some pics of the beast.
     

    Attached Files:

  4. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    one of the original failed bridge, and the new one in place, failed also.
     

    Attached Files:

  5. davenn

    davenn Moderator

    13,496
    1,830
    Sep 5, 2009
    This really makes no sense unless the transformer has a major fault in it

    16 amps on the secondary side is only going to be maybe 500mA to maybe 1A on the transformer primary

    don't know where the heck your 30 Amps is coming from ????
     
  6. duke37

    duke37

    5,297
    739
    Jan 9, 2011
    The KBPC5010is 50A, I could not find details of the QBPC5010.

    The bridge will dissipate over 1W for every Amp.
    The heat sink compound needs to be thin and cover the entire contact suface. I made the mistake of using too much compound on an electron microscope water cooled focus supply.
     
  7. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    I replaced the bridge and cleand up a bit. First I cut the bridge out...The electronics part works, but I am not using the supply it untill I know what's up with it. I removed the bridge and gave with my labo psu 25 on the + and the - where the bridge used to be. No problem.. Clean supply, working only able to test upto a few amps due my labo supply is only 3 amps.

    So now there is a new bridge rectifier in it. Head dissapation was not an issue helas, when it failed the metal cool block was warm enough.

    I noticed where the bridge blew up the bridge was not properly soldered to the board, however the ac wire from the transformer that fed it directly was attachted to the bridge. and there is no ac track going anywhere, so that should not matter?

    I have put the same bridge, but this time a black looking one, with a bit longer legs and used a lot of solder and solder paste, it is now shining and completely within the pcb. Though AC is fed with the wires coming from the transformator I made sure that those where in good contact, but they where before also. So put them back in.

    I removed the 8x paralell caps after the bridge, but they have no sign of leaking and they measure correctly. Also they charge and hold the charge.

    The AC meter is put betweeen on wire of the output of the transformator, roughly 18volt AC, 24 volt after the bridge. (x1.4). Since this is a linear design it is not efficient. So roughly every amp metered is doubled taking measurements there. I had the amp meter from another project, and I knew it would indicate not the used amps there. If this supply works, I will scan the scale with a scanner and photoshop it to give the output more or less better.. There is not much room for other meters in it.. And I don't mind really. I know it is roughly /2. And for now I like the amp meter making a small noise that I am on high power when transmitter is taking a lot.

    Some early work was done a lot better now, but no shorts found. helas.. Nothing.. It works.. But still not clear why the bridge rectifier failed again. A friend suggested to test the 4*2N3055 next day.. However my labo supply does not indicate abnormal power usage when I feed the circuit directly. Only tested with 2 amps load.
     
    Last edited: Dec 1, 2016
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,299
    2,737
    Jan 21, 2010
    The peak current through the rectifier into filter capacitors will be many times higher than the average current drawn from the power supply. That may be a contributing factor.
     
  9. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    Today I found also that two 2N3055 are not working.. Might be more complex. I have spares but need them verified 100%.
     
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