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AC/DC Adapter Question

Discussion in 'General Electronics Discussion' started by mmitsch, Dec 18, 2021.

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  1. mmitsch

    mmitsch

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    Dec 18, 2021
    i want to be sure the power supply in the picture is working. I tested with a voltmeter and it read 13.8 V. I put the positive probe on the shaft of the connector and touched the ground to the barrel. Is there another test and is the 13.8 V reading unusual?

    This is the adapter for an elliptical exercise machine console and I want to rule out the power supply as suspect prior to getting a new console (the current one isn’t working).

    Also, is the MKD-48091000 a common P/N? Do you think I can buy one online or should I go back the the elliptical manufacturer?

    Thanks!

    [​IMG]

    https://imgur.com/gallery/shRWuAf


    [​IMG]
     
    Last edited: Dec 18, 2021
  2. AnalogKid

    AnalogKid

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    The two images did not post, but the link works. So does the adapter.

    That is an unregulated linear power supply. Transformer >> rectifier >> filter capacitor. The average value of the output voltage will drop to the rated value when the output current is at or near the rated value. With a lighter (or no) load, the output voltage increases. How much it increases depends on the size of the filter capacitor, the wire sizes in the transformer primary and secondary, and the quality of the steel in the transformer core.

    ak
     
    mmitsch likes this.
  3. mmitsch

    mmitsch

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    Dec 18, 2021
    Thank you very much for your response!

    I had a tough time figuring out how to post a photo and finally tried Imgur. Guess that worked!

    I’ve got a new console coming so I guess that’ll fix it. Was hoping to find a tech to troubleshoot.

    I appreciate you getting back to me and sorry for the image issues!
     
  4. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Best to check voltage under a load.
    Try putting a low wattage automotive lamp across the output and remeasure.
    You could also try a resistor of roughly 10-15Ω across the meter leads when testing, but only leave it on briefly or it will get very hot unless it's a high wattage rating.
    Some times a power supply will show a voltage with no load but then voltage will disappear under a load indicating its bad.
     
    Harald Kapp likes this.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Direct upload to this forum works best for image sizes < 300 kB.
     
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Here is a Google search result that might help...
     
  7. mmitsch

    mmitsch

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    Dec 18, 2021
    I got the new console in and installed it. The lights didn't come on bur there was a high pitched noise. Now I'm wondering if the AC Adaptor is bad. I tested again and show 13.8 volts. I did notice it gets hot when plugged in with no load -- is this usual?
     
  8. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Usual is a rather vague term in this context! It is usual for power supplies to run warm, and without forced air cooling this could be considered hot.

    As @AnalogKid noted in his post #3, this is a linear power supply. It will get warm during use. It probably has a small, inefficient, heat-producing transformer that reduces the input rated 120 VAC at 0.3 A to a sufficiently lower voltage that can then be rectified, filtered, and possibly applied as the input to a series regulator to achieve an output of 9 VDC at 1.0 A.

    If the rated 0.3 A input current is typical under load, then 36 watts is dissipated in the primary of the transformer while delivering only 9 watts to the load after the linear regulator, filter capacitor(s), and rectified secondary voltage. This is terribly inefficient and the reason why most of these low voltage DC power bricks now use a switch-mode power supply (SMPS) for a lower temperature rise. SMPS also features a wide input voltage and input frequency range that automatically operates almost everywhere in the world where there is electrical power available.. So, yeah, I would expect the case of the power supply to be substantially warmer than ambient temperature. But not so hot as to cause burns to the skin when touched. Almost no electronics runs that hot unless something is defective, or unless it is a high-performance piece of military hardware.

    You could purchase a new "back-up" power supply with the same input and output rating and compare temperatures if you think this is a problem. However, since the new console also doesn't work, a new power supply would next on my list of things to try. Before buying a new power supply, I would try to power up (whatever it is you are trying to power with the existing supply) with a battery to see if that works... maybe eight 1.5 VDC alkaline D-size cells connected in series, or a single 12 VDC lead-acid battery would get your console running. If so, that would verify that your old power supply isn't going to work.
     
  9. Martaine2005

    Martaine2005

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    May 12, 2015
    Have a look around your home, you must have an adapter to try out the console.
    9V @ 1A is what you have.
    Find another 9V adaptor with upwards of 750mA.
    I have for example, my router booster, portable CD player, bench multimeter, audio mixer amongst others that have a 9V adapter. If you’re lucky, one will have the same DC connector and polarity.
    It’s got to be worth a look.

    Martin
     
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