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Thread: dongle to convert USB DC power cord to old fashioned 3mm plug

  1. #1

    Default dongle to convert USB DC power cord to old fashioned 3mm plug

    I have a lot of equipment that runs on batteries or a wall wart DC transformer. The modern battery power packs all have a USB plug as the power supply to plug into the device. I need to convert that to a 3mm(?) round plug, the kind where one conducter is the entire surface and a hole in the end (the socket has a round rod inside it).

    Better would be a cord that has the size USB plug on one end (to go into the battery pack) and the round plug on the other.

    Or where could I buy a round plug, and cut the end off a USB-USB cord. Have to know which conductor is + & - though.

    Which size USB plug is the end that goes into the device - big or tiny?

    The only good part of this is that battery packs seem to be able to supply anywhere from 3-12 VDC, so I can use the same supply for any piece of equipment.

  2. #2
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    I've found 5mm plus to USB A plug cables and clip leads to USB A cables but haven't seen a 3mm on but you could try Ebay.
    I can't post a link here even if I found one due to the restrictions.
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  3. #3

    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

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    I did that THREE times already !

    Using a ruler ite seems to measure 3/8" more closely than 4mm. Is that a standard size?
    What is the name of this kind of plug, with the hole in the end?
    Might have to make my own cord.
    If anyone has a link to buy it, message me.
    TIA

  4. #4
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    You may have to make one. Without exact dimensions or the device it plugs into I would have to lean towards the most common plug size.
    https://en.wikipedia.org/wiki/Coaxial_power_connector 5.5mm is the most common size the page says 3.5mm is the second most common size which may be the size you have but they list 3.2-3.8mm. If it is a black end then it is likely an older size the newer ones are often color tipped with yellow being the most common I've seen. I had all sorts of fun trying to find a plug to fit a Sony Blu-Ray player that has a 12v input.
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  5. #5

    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    Radio Shack, where art thou? I miss the days when I could travel to a pleasant location and just keep sticking it in until it fit. Worked on my honeymoon & no problems since...

    With a magnifying glass, the OD seems to be 4mm pretty exactly, and around 5/16" with less precision.
    The ID seems to be 2.5 to 3mm.
    There is no exact match in the wiki page list.

    The CD player is an Emerson shaped like a disk, manuf in 2004, its transformer is 6VDC 400mA.
    The socket is 4mm OD, the internal pin is harder to judge, at least 1mm, not more than 2mm.

    If I had mad soldering skilz, I'd open it up and either install an USB type socket, or solder wires coming out ending in a USB type socket.

    The alternative seems to be to purchase a boom box CD/radio, but they usually want 6 batteries, C or D, and the ads never show the type of power connector for AC/DC. I would get one with the modern USB type power socket.

    Someday I'll burn my CDs and go digital, but that's a whole long process. Maybe I should hire a teenager to do it for me & get it all indexed & playlisted...

  6. #6

    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    Discovered they make Li-ion power packs with a DC5521 plug - which sounds like 5.5mm OD, 2.1mm ID.
    This on the warrior lady site for about $25.
    TalentCell Rechargeable 12V DC Output Lithium ion Battery Pack for LED Strip/Light/Panel/Amplifier and CCTV Camera with Charger, Multi-led Indicator Black (3000mAh)

    But are these smart enough to reduce the max 12V down to what the device wants?

  7. #7

    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    The above seems to be 12v only.
    This one has 12, 9, 5 volts, but each is a different jack. And the 5v, which is what I need, is, you guessed it, a USB jack
    Crap.
    TalentCell Rechargeable 12V/11000mAh 9V/14500mAh 5V/26400mAh DC Output Lithium ion Battery Pack for LED Strip and CCTV Camera, Portable Li-ion Power Bank with AC/DC Charger, Black


  8. #8

    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    hopeful: 663 results for "usb to round power plug"

    I see items with 8,10,12 sizes of plugs that adapt to the USB cable.
    I think mine might be 4.0 x 1.35 because mine & the example have a BLACK TIP.
    The brand in Onite, 12 sizes.
    I'd rather buy the Belkin, but that size is not in their 12 pack.

    I'm guessing that the second size is not the ID of the opening in the plug, but the dia of the pin in the female side ?
    Not sure...
    Last edited by lumen aeternum; 04-10-2021 at 08:39 PM.

  9. #9
    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    I see 4mm x 1.7mm plugs but nothing larger ID than that.
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  10. #10

    Default Re: dongle to convert USB DC power cord to old fashioned 3mm plug

    For reference, here's the largest selection I have found that actually lists all the sizes:
    Description: Female 5.5x2.1mm to Male 28 different size DC Connectors listing:
    1: 7.9x5.0mm with center pin: main for Lenovo IBM, ThinkPad
    2: 7.6x2.5mm round
    3: 7.4x6.0mm octahedron
    4: 6.3x3.0mm
    5: 6.0x4.0mm
    6: 5.5x3.0mm
    7: 5.5x2.5mm
    8: 5.5x2.5mm
    9: 5.5x2.1mm: for Asus laptop
    10: 5.5x2.1mm
    11: 5.5x1.7mm
    12: 5.5x1.5mm
    13: 5.0x3.0mm
    14: 5.0x2.5mm
    15: 5.0x2.1mm
    16: 4.8x1.7mm
    17: 4.8x1.7mm
    18: 4.5x3.0mm: for HP Stream 11 13 14, Pavilion Envy Elitebook Dell Latitude Inspiron XPS Precision
    19: 4.0x1.7mm: Sony PSP,
    20: 3.5x1.35mm
    21: 3.0x1.1mm: for Acer Chromebook 11
    22: 2.5x0.7mm: for Samsung Chromebook 11
    23: 2.35x0.8mm
    24: 2.0x0.6mm
    25: for toshiba 4pin
    26: for dell 3pin
    27: 3.5mm mono plug
    28: 2.5mm mono plug

    3x DC Power Cables Parameter:
    1: 1.2m 5A "+ -" Polar Connector Test Line to DC 5.5 x 2.1mm
    2: 1m 3A DC Famale 5.5 x 2.5mm to DC Male 5.5 x 2.1mm
    3: 1m 2A USB 2.0 to DC Male 5.5 x 2.1mm


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