New B&K DC Power Supply Smokes Its Fuse

Discussion in 'General Electronics Chat' started by monster_catfish, Jun 29, 2011.

  1. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    110
    107
    Hi all,

    I recently took delivery of a B&K Precision Model 1670A Regulated DC Power Supply, but found to my dismay that the male plug on the supplied power cord would not fit any socket or socket adaptor I own.

    No problemo, I thought to myself, foolishly. From my collection of new and used power cords, I selected a pair of cables whose ends matched the power supply and mains power-strip connections, noting to my relief that the color codes of the 3 wires in both cables were identical, namely brown, blue and yellow.

    In a few minutes I had matched colors and joined the wires, assuming, foolishly again, that my hot, neutral and earth connections were properly made for safe operation of the power supply.

    Well, the satisfied smirk faded from my face right quick when I hit the power button, heard a loud DC hum, saw the display window light up for a fleeting moment, and then, to my horror, watched the unit lose all power.

    Checked the fuse at the power-cord socket, and it was smoked the instant I applied the 220 volt AC mains we have here. The unit, by the way, is rated for either 115 or 230 mains, so there was no error in that regard.

    Given that I did carefully check continuity in my DIY power cable, to ensure that no mistakes were made in my connections, my question here is whether there exist discrepancies in the protocol for the connection of color coded power line wires, such that my ASSUMPTIONS about simply matching colors, when connecting up my new power cable, were flawed to start with.

    I am really worried that my costly new B&K DC power supply has been ruined right out of the box, even before I got to use it once. Before I attempt to diagnose the situation any further, however, I thought it might be a good idea to ask the pros here what recommendations they may have, besides, of course suggesting that I don a conical foil hat and sit in the corner for a few hours as punishment for my idiocy.

    Any comments would be appreciated. Thanks in advance.
     
  2. #12

    Expert

    Nov 30, 2010
    16,247
    6,742
    We don't have many members from Ghana. I only know USA color codes...black, white, and green.

    Anyone from Ghana please help this person.
     
  3. awright

    Well-Known Member

    Jul 5, 2006
    84
    7
    As you found, color coding of wires is not a reliable method of determining proper wire connections, especially when you are dealing with equipment from countries other than your own.

    You say the equipment was rated for either 115 or 230 volt supply, but you do not say that you actually checked that the equipment was, in fact, set for 230 volts. Did you confirm that the equipment voltage selector switch or internal links were set for your voltage? "115/230 volts" generally does not mean that you can plug into either voltage without resetting for the appropriate voltage. Unfortunately, some newer switch-mode power supplies for computer equipment CAN handle inputs from 90 volts to 250 volts or so, possibly leading the unwary to believe that common bench equipment can do the same. Not true, in most cases.

    It is interesting and surprising that the 1670A manual does not appear to address the issue of setting the equipment up for the proper line voltage or comment on how to make that setting. (But how many of us study the manual before plugging in, anyway?) Perhaps you can embarrass the company into fixing your unit without charge based upon that oversight in the manual. I would be surprised if they did, but it might be worth a try.

    If it's any consolation, most of us have made a few foolish mistakes like that if we've been in the game for any length of time. I have (but I'm not saying what).

    Good luck.
    awright
     
  4. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    110
    107
    Awright I thank you for this insight. I did scour the manual, but didn't spot any mention of manually selecting 115 or 230 volt operation, and, there is no external switch that could be for that purpose visible on the chassis.

    The users manual and chassis do specify both 115 and 230 volt mains compatability for this power supply, with no further elaboration, which is why I arrived at the obviously wrong conclusion that the unit would automatically configure itself like those universal supply-voltage shavers do, when plugged in anywhere globally.

    #12 your caution about color codes is appreciated as well. I've got a replacement fuse on the way, and will be exceedingly careful before I try to plug this power supply in again.

    Another odd thing I noticed is that the user's manual calls for a 1.6amp fuse applicable to 230volt mains useage of this DC power supply, and a 3amp fuse for use with 115 volt AC mains. My newly purchased unit just blew the 3 amp fuse that it was shipped with, suggesting it had been set up for 115 volts AC and NOT 230 volts.

    All told, there will definitely be a considerable pucker factor when next I test this unit, fer sure.
     
  5. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    110
    107
    Holy mackerel ! That 115/230 selector switch was present, but was in a very obscure location, as suspected by Awright in his post above. It took a flashlight and a magnifying glass to read the inscription on that tiny switch, which was not labelled at all, and was recessed behind a plastic cover on the underside of the unit.

    Went back to the user manual, and there is definitely no mention of the existence of that mains voltage selector switch. So now I'm holding my breath to see if the unit still works normally after this misadventure. When the fuse blew, there was no burning smell, which I hope is an indication that there was no other component damage.

    Whoever wrote the manual for this B&K Precision DC power supply, and left such a glaring omission relating to input voltage selection, deserves a spell breaking frozen rocks in the depths of a few Siberian winters, or better still, should be presented with a lifetime's worth of mandatory-attendance tickets to Barry Manilow concerts.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    That's interesting, because the datasheet on that supply from BKprecisions' website indicates: Power Requirements 108 - 132 VAC, 60Hz
    There is no mention of other input voltage ranges or line frequencies.
    Datasheet link: http://www.bkprecision.com/products/docs/datasheets/1670A_datasheet.pdf

    Before you power it up, you might have a look at what's on the secondary side of the transformer. If there's a rectifier bridge feeding filter caps, you might have also blown one or more of the rectifiers in the bridge, as you would've exceeded their current/voltage rating by a fairly large margin, as the fuse installed was twice as large as it should have been. If you try to operate it with one of the bridge rectifier diodes blown, you will have excessive ripple current on the filter caps, which can cause them to overheat and burst when the supply is under load.
     
  7. monster_catfish

    Thread Starter Active Member

    Mar 17, 2011
    110
    107
    Yeeeeehaw ! Its aliiiiiive, Igor, its aliiiive heh heh heh. Ahem, sorry about that, but I truly am relieved to say this seems to have ended well, against all odds.

    A little euphoria is definitely in order here, for after setting that very well hidden switch to 230Volts, and replacing the fuse, this DC power supply lit up and tested OK, though with no load as yet, so maybe bearing Sgt. Wookie's insights in mind, I should not go into full jubilation mode yet.

    Nonetheless, Whew, and what a relief. I'm so stoked right now that I don't know whether to have a bottle in front of me, or a frontal lobotomy.

    Will report back after a more exhaustive test.
     
  8. #12

    Expert

    Nov 30, 2010
    16,247
    6,742
    With enthusiasm like that, I can forgive you for getting caught with your stupid on. (After all, it happens to everyone, occasionally.) Visit often. We might be able to kick some of the stodgy out of this website.
     
    Last edited: Jun 29, 2011
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