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Cool flea market find today

Discussion in 'General Ham Radio Discussion' started by GA1dad, Jul 13, 2019.

  1. GA1dad

    GA1dad Member

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    This morning I went to the local flea market looking for a antenna to use on a project. Had I not been looking, there would have been 10 for sale,,, but alas there were none. However, I stumbled upon an Astron RS-20a that was missing the cord. Asked the seller how much and his first response was "what is it?",,, that was a good sign. After I told him it was a power supply he responded "what about $5?". I'm not gonna lie,,, I tried for $3 since I couldn't test it,, but he dug in at $5.

    So I got it home, dug out a cord and plugged it in and heard the hum,,,, VOM says 13.8V,,,,,, cool! I haven't load tested it yet, but you can't beat a 20 amp supply for $5.00!!


     
    999, 6meter, Mudfoot and 9 others like this.

  2. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    Nice! I gotta say, today was a good day...
     
    GA1dad likes this.
  3. sunbulls

    sunbulls Sr. Member

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    Nice! Heck, it's worth $5 just for the case and heatsink. If the transformer was bad, I have a rebuilt microwave oven transformer (now 18v) that would fit nicely inside.
     
  4. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    Impressive. Most impressive. Tell more of this food warmer transformer you have.
     
    S&W357 likes this.
  5. sunbulls

    sunbulls Sr. Member

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    I must mention that any attempt made to remove one of these microwave oven transformers (MOTS) from the cabinet is dangerous. There is high voltage capacitor that needs to be discharged first! Touch a well insulated screwdriver across its terminals several times to be certain. There are many on-line video examples about converting these MOTS for various purposes. Most of them deal with just the removal of the high voltages secondary that has a large number of windings with fine wire and replacing it with a heavy gauge wire with something less than 50 turns,depending. The following links will give you a better idea of what’s involved.





    I used my Dremel cutting disk on my secondary for fear of damaging the primary. Others typically use a chisel or hacksaw blade. At present I used 14 G stranded insulated wire, but I may change that to heavier G enameled copper later, depending if excessive heat occurs on the winding after the regulator and pass transistors are finalized and under a load. I also plan on using basically the same regulator circuit as Astrons 20A, but won’t push it beyond 10 amps, at least at first. The down side of these MOTS is their lack of efficiency, especially being used as a low voltage supply vs their original attended high voltage purpose. That results in extra wasted household power and heat created on the primary. The solution involves adding more windings on the primary, but that requires cutting the transformers core apart to add those extra turns, then weld the core back together again. That’s a little much for me. If I can achieve 10 amps at 13.8 V with little heat involvement, I’m happy. Otherwise I’ll configure it as a low amperage battery charger with several voltage taps.
     
    GA1dad and Shadetree Mechanic like this.
  6. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    Very cool. Thanks for sharing.
     
  7. GA1dad

    GA1dad Member

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    Very cool,,

    I hooked a 25 amp HTX-10 to the $5.00 supply yesterday and it seems to be operating just fine.
     
    Mudfoot likes this.
  8. 6meter

    6meter Well-Known Member

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    Very nice deal - an Astron 20 amp power supply for only $5.

    The HTX-10 manual calls for 7 amps at 12 volts so that gives you a lot of overhead.
     
    GA1dad likes this.

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