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I’m looking for an elegant solution to power an old radio with 220v dc

Discussion in 'Power Electronics' started by w0pjb, Jan 24, 2021.

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  1. w0pjb

    w0pjb

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    0
    Jan 24, 2021
    The bc-348 radio was powered by a dynamotor with output rated at 70ma @ 220V dc according to spec.
    I have 120V AC on the house mains. I’m keeping the radio on DC power.
    I have one schematic (attached) I’m looking at but that involves 2 transformers which I could work with but there has to be a way to get there with a switch mode power supply with maybe a zenor diode. Designing that is way beyond my skillset.

    Here is the outline for the solution for 2 transformers.
    Transformers T1 and T2 are low-voltage
    transformers with 120-volt primaries. They are
    hooked up in reverse so that the high voltage
    appears at the output. Use transformers with
    12-volt, 2 amp secondaries for 12-volt operation; with 24-volt, 2 amp secondaries for 24-volt
    operation.
    PNP power transistors are 2N6109 or equivalent. These must be heatsinked. Check the data sheet for your transistors to see if the heatsink tab is connected to internal circuitry. If so, and if your “dynamotor” is to be built on a metal panel or chassis, you’ll need to add mica insulators under them. Diode D1 is a 500-volt (or better), 2 Ampere unit (1N4007 or equivalent). Capacitor C1 is a 40-80 uF, 300-volt electrolytic. Resistors R1 and R2 are 10,000-ohm, 1-watt.
     

    Attached Files:

  2. Martaine2005

    Martaine2005

    3,214
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    May 12, 2015
    Maybe an easier way is with a 220V-120V voltage converter, Europe to USA. It’s essentially a single transformer which you can then use in reverse. Add the bridge rectifier and smoothing caps for DC.
    Just an idea to get the thinking caps on..

    Martin
     
    davenn likes this.
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    2,502
    Nov 17, 2011
    Any 120 V to 220 155 V transformer (or 220 155 V to 120 V transformer in reverse as suggested by Martin) will do with the help of a rectifier and smoothing capacitor. [Edit: corrected transformer ratio to account for peak values.]
    The rectifier and capacitor will be needed in any case. The single transformer is a so much more simple solution than an SMPS.
    You can't use a standard mains transformer with an SMPS: mains transformers are designed for 50 Hz or 60 Hz operation. An SMPS operates in the kHz range. The standard mains transformer will not operate well in that frequency range and would be way to big, too. SMPS transformers usually are small ferrite types.
     
    Last edited: Jan 25, 2021
  4. bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    When you use a 220 V to 120 V in reverse, the output voltage will be 220 V AC, when rectified the voltage will be about 310 Volts DC.

    Bertus
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    10,999
    2,502
    Nov 17, 2011
    I must have been still a bit sleepy. Of course, after rectifying we'll have the peak value which is sqrt(2) times the RMS. Therefore the transformer ratio needs to be changed. I updated my post #3.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    10,999
    2,502
    Nov 17, 2011
    According to this website (German) the elegant solution would be to use a mains power supply NG-V, if you can find one.
     
  7. bertus

    bertus Moderator

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    Nov 8, 2019
  8. w0pjb

    w0pjb

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    Jan 24, 2021
    I have the bc-348R.
    So it appears they have it right with the original solution of 2 tranformers. I would have to hook up the oscilloscope after I have it wired in and see what I get.
     
  9. Martaine2005

    Martaine2005

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    May 12, 2015
    Apparently, it was common to wire all the series-parallel heaters in parallel. This meant the heaters run on 6.3Vac rather than the original 24v/28vac.

    Martin
     
  10. bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    It depends on the type of tubes/valves.
    There are tubes/valves that have the same current, but different voltages.
    There are tubes/valves that have the same voltage, but different currents.

    Just look in the datasheets of the tubes/valves for the type used.

    There are a couple of numbering systems for vacuum tubes/valves:
    https://webspace.science.uu.nl/~tel00101/FotoAlbum/RadioCorner/Articles/TubeTypes.htm
    https://www.tubemuseum.org/SearchResults.asp?Cat=30

    Bertus
     
  11. Martaine2005

    Martaine2005

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    May 12, 2015
    bertus likes this.
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