Plasma disc PSU overheating

Discussion in 'General Electronics Chat' started by roblloydwales, Jan 19, 2016.

  1. roblloydwales

    Thread Starter New Member

    Aug 20, 2009
    9
    0
    Hi all, Please be patient as I am a novice, I recently bought a plasma disc which is designed to operate on 2 x AA batteries, I really would like to run it from a plug in power supply, so I attached it to a PSU with 5V, 500mA USB output, it runs great for a few minutes, but then starts to fade and the PSU overheats. The plasma disc runs for hours on a 5V battery pack and is drawing around 250mA.
    Any ideas as too what is happening and how to solve the problem would be greatly appreciated.

    Here's a link to the plasma disc if it's any help, perhaps someone has done this in the past.
    http://www.ebay.co.uk/itm/New-Fancy...ng-Plate-Home-Disco-Party-Decor-/230860613677
     
  2. #12

    Expert

    Nov 30, 2010
    16,346
    6,833
    Don't connect it to the power it was not designed for.
     
  3. sailorjoe

    Member

    Jun 4, 2013
    361
    63
    Two AA batteries would only generate at most 3 Volts for power. But depending on how it's wired, it could be only 1.5 Volts. If you have to pursue this, try a 3.3 volt wall wort. If that still causes problems, build a 1.5 volt power supply that runs off your 5 or 3.3 volt wall worts.
     
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  4. roblloydwales

    Thread Starter New Member

    Aug 20, 2009
    9
    0
    Thanks for the replies, but your missing the point guys, the disc runs perfectly for hours powered by a 5V (or more precisely a 4.5V) rechargeable battery that is designed for running USB powered devices.
    There's not much drain on the battery and doesn't get warm.

    The AA batteries are in series, so definitely 3 Volts.

    Built a 3V 1.5A regulator (LM317) circuit yesterday, it overheats in minutes, replaced LM317 with LM350 and still overheating, but like I said, the current draw is only around 250mA so cant see that being an issue.
     
  5. #12

    Expert

    Nov 30, 2010
    16,346
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    Your problem is with the regulator circuit. Post your schematic for the regulator. Be sure to include the voltage you are feeding it.
     
  6. roblloydwales

    Thread Starter New Member

    Aug 20, 2009
    9
    0
    It's just the bog standard LM317 circuit with R1 = 240 ohm and R2 = 330 ohm, supplied by 12V, 2.5A PC power supply
     
  7. #12

    Expert

    Nov 30, 2010
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    You are missing the capacitors which stop the regulator from oscillating. Look at the datasheet for the proper construction.
     
  8. roblloydwales

    Thread Starter New Member

    Aug 20, 2009
    9
    0
    Found this on the data sheet, I'll give it a go tomorrow, thanks #12.
     
  9. #12

    Expert

    Nov 30, 2010
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    Now that I'm not in a hurry to get to the bank before it closes, 12 volts reducing to 3 volts at 1/4 amp creates 2.25 watts of heat in the regulator. A TO-220 package will be at 112.5C above ambient temperature, very, "burn your fingers" hot with no heat sink. You need to glue a coin to the chip or give it a "real" heat sink so it has more radiating surface.
     
    Last edited: Jan 22, 2016
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