Power supply question.

Discussion in 'General Electronics Chat' started by Fyreater21, Oct 15, 2010.

  1. Fyreater21

    Thread Starter New Member

    Oct 15, 2010
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    I am new here to this site. I probably have just enough knowledge to get me in trouble, so I decided to ask here for some insight and help. I am into amateur radio and have been able to get my hands on a transformer that has an output of 12V and 16V at 70Amps from 110 volt input. I am looking to design a power supply for my mobile equipment. :confused: I have been looking at circuitry and schematics but nothing I've seen even talks about this range of amperage. Do I own a door stop or is there a viable solution? If there is a solution, I would greatly appreciate schematics or a lead to finding a solution.
    I am looking to be able to connect 4 pieces of apparatus to the supply and need a constant 13.8V. The amperage is important for the 200W amp, radios, and antenna tuner. (40 meter and 10 meter).

    Thanks
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Welcome,
    Amateur radios require lot of power but 70Amps ??? I think u are pushing this too far.

    A 70A transformer will be as heavy as a welder. Ever seen this.

    For radios, PSU are available.
    Did u try googling
     
  3. Fyreater21

    Thread Starter New Member

    Oct 15, 2010
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    R!f@@, Yea, I googled it, but the stuff comes up like a guarded secret. There 100 amp units 80 amp but no one seems to want to give up a schematic. The parts are not that expensive, even a STM 400V 90A Bridge rectifier is only $13.65. My problem is in designing an operational amplifier like an LM chip to handle the current. I would like to end up with a power supply that adjusts from +3 to +24 VDC.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Question is , Do u have the transformer?
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Easy enough, standard regulated supply control IC with a lot of pass transistors & a huge heat sink.
     
  6. Fyreater21

    Thread Starter New Member

    Oct 15, 2010
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    R!f@@ Yes I do.
     
  7. Fyreater21

    Thread Starter New Member

    Oct 15, 2010
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  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    What is the rating written on ur former
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    A simple shunt bypass type power supply would be easy to implement, for increased amperage you would simply add more shunt bypass transistors(4 should be enough) and put them on a BIG heatsink.

    I KNOW that schematics for these power supplies are all over the web. Do some more searches @ www.images.google.com
     
  10. someonesdad

    Senior Member

    Jul 7, 2009
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    While I understand you've already purchased the transformer, another option would be to just buy a power supply such as this 500 W switching supply. It's certainly not as cheap as making your own (nor as fun), but it would get you running quickly.
     
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
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    What he's trying to build isn't that hard, what I dread in situations like that is coming up with the heat sink.

    From time to time you'll find BIG heatsinks on eBay at great prices, often these came from those Peltier coler refrigerators.

    I've also been known to adapt almost anything aluminum or copper in combination with other pieces to make my own. I once hit a surplus sale on some website that had pallets full of older heatsink/fan combos that related to a CPU socket that wasn't really used anymore, however the heatsink/fan combos were still rather substantial. A rather hefty copper bus bar from an electrical supply surplus house + some thermal adhesive and I had quite the setup. I've used pieces of aluminum door threshholds from Home Depot as well but if you find a good souce of flat, thick copper it's worth jumping on - especially because so much has been melted down lately.

    A shop that sells/supplies/rents/repairs welding equipment or anything having to do with charging "tractor batteries" (warehouse equipment) will probably have some old units that have bad transformers. Guess what's inside on the rectifiers? Huge heat sinks.

    Also remember that a heat sink doesn't need to be flat and exactly cover the area you need to serve, heat moves and the idea is to get it into the air even if it has to take a few sidesteps in doing so.
     
  12. Pich

    Active Member

    Mar 11, 2008
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  13. Fyreater21

    Thread Starter New Member

    Oct 15, 2010
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    Pich, thank you. I know how to google, I was looking for a better idea. Guess I well have to use about 7-3055's paralleled and then work on keeping some head room voltage to avoid too much of a drop under load.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    More than that.

    Count on about 8A per transistor. More than that, and you're really pushing it. You're going to need 9 for the pass transistors, and at least 1 to supply their base current.

    You're also going to need a LOT of capacitance for C1; 250,000uF or more.
     
    Last edited: Oct 17, 2010
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    This is do able. If OP tries. I did made a 10Amp one and is pretty rugged.
    Don't see why OP can't

    I asked for his former rating to give him sum info from my part.

    Op did not reply to tht
     
  16. tom66

    Senior Member

    May 9, 2009
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    And make sure you have some good quality caps. There will be a lot of ripple current going through them (sometimes 10x the load current.) Cheap caps will just melt.
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I checked his link. OP, Are u referring to the 110V to 16V @ 70A transformer.

    If u have bought it than I suggest u plan on buying the bridge and the filter caps
     
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