Wallwart help please

Discussion in 'The Projects Forum' started by tng80, Aug 18, 2009.

  1. tng80

    Thread Starter New Member

    Aug 18, 2009
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    Hi,
    I currently have a wallwart that puts out 12v 3.67a. I need to make so it puts out ~9.5-10v 2.5a. I believe the amps arent that big of a deal since what I'm plugging in will only pull what it needs. Is this correct? Also what would be the best way to make this work?

    Thanks for any help
    TerryG
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    It would probably be less expensive to buy another 10 volt 2.5 amp wall wart than to try to regulate the output of the one you have down. With wall transformers, what you have is all you have. If yours is actually regulated, you would have to non-destructively open it up, figure out how the regulator works, and rejigger it down to 10 volts.
     
  3. tng80

    Thread Starter New Member

    Aug 18, 2009
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    I have one coming in the mail but its kind of a need it now situation. Thanks for the info tho.

    Terry
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Is yours regulated? There are things you can bring that voltage down, but if it isn't regulated (which is more likely) there is not too much you can do.

    My thought was to stick 3 or 4 largish diodes in series. Regulation sucks with this idea though, I would even define it as not regulated.
     
    Last edited: Aug 18, 2009
  5. tng80

    Thread Starter New Member

    Aug 18, 2009
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    I dont believe it is but I may be wrong. It's marked 120VAC 60Hz 500mA max on the input side and 12VAC 3.67 A on the output. Sorry to sound like a dummy but this is my first time messing with power like this. I'm used to pc power supplies.

    Thanks
    Terry
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You could try to put a low drop stabelizer behind the walwart.
    A LT1085 will do the job, it can work upto 3A.
    See tha datasheet for more info.
    (the dataheet contains info on LT1083, LT1084 and LT1085).

    Greetings,
    Bertus
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Don't use this wallwart, it is not a DC power supply. It is marked with 12VAC, that means it has AC, not DC, on the output. You will smoke whatever you're trying to use it for.

    If you want to turn this into a regulated power supply it just became more complicated. I get the impression you don't have the background for a major project yet, which this is turning out to be.

    Are there any stores in your area that sell electronics?
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hi Bill,

    I overlooked the 12 VAC. You are right.
    When you want to turn the AC walwart to a powersupply you will need some more stuff.

    Greetings,
    Bertus
     
  9. tng80

    Thread Starter New Member

    Aug 18, 2009
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    Theres a small radio shack which seems to have more rc cars than electronics. Im trying to make an adaptor for one of those little asus eee pc laptops if anyone is curious.

    Thanks for the replies and keep them coming. I'm not scared to give it a shot. Learn by doing and all that.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Been there. Did that. Check the end of this thread.

    http://forum.allaboutcircuits.com/showthread.php?t=10339

    Sounds like you're in the same boat as my boy was (same computer, same problem). I wasn't too happy with the one I built (it works, but barely), so another design is in the works, but not there yet.

    Your current specs are a lot bigger though, his was around 2.5A. I would consider the 9.VDC a pretty hard spec, 9.7 should be max. Are you willing to do this quick an dirty think a chunk of wood to use as a mount, and a largish chunk of metal for a fan, and a fan to cool it all down.

    Are you serious about doing this? The new supply will likely get there before you finish this.

    You might be able to use a PC power supply for the base power supply, take the +12V output and regulate it down. Problem with this approach is not all PC power supplies are easy to use, some require loads on all the power supply outputs.
     
    Last edited: Aug 18, 2009
  11. tng80

    Thread Starter New Member

    Aug 18, 2009
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    I would definitely be game for using a pc power supply if need be. I've got my girlfriend all up in my a** about getting it done for reasons I can't really discuss (nothing illegal). If you have an idea for using a pc psu I'm all ears. Thanks Terry Edit: I found a LM317T adjustable regulator at radio shack's website. Would this be usable with a heatsink? Link: http://www.radioshack.com/product/index.jsp?productId=2062601 Edit2: I don't think that'll work since it only puts out 1.5a, right?
     
    Last edited: Aug 18, 2009
  12. Wendy

    Moderator

    Mar 24, 2008
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    The LM317 is not usable as is (1A max for a TO220 case), but with a couple of 2N3055's, which are also available from the shack, could be made so. I've got to get to be, but the datasheet has the information you need to do this. You WILL need good heat sinking, and you could proabably use the fan from the computer PSU to provide air flow. Good luck.
     
  13. tng80

    Thread Starter New Member

    Aug 18, 2009
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    Got the parts lined up, now if I can just figure out how to set them up. Thanks Bill for your help. Man, I've got a headache...
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    When I get a chance I'll go through it, assuming someone else doesn't beat me to it. Not able to at the moment, but later today I should have some time.

    When you build this be prepared to test it. I would recommend using 1, then 2 12 lamps such as is used on a car. You DON'T want to make a mistake here, computers cost more than power supplies, a lot more.
     
  15. tng80

    Thread Starter New Member

    Aug 18, 2009
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    I manage a parts store so getting car bulbs to test with won't be a problem. Thanks again for all the help.
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    OK, here are a couple of schematics that might be useful in the datasheet, which is what I was referring to.

    [​IMG]

    [​IMG]

    Neither one of these are meant for beginners, so if you have any friends with technical experience this is the time to ask a favor. Like I said, it is a pretty technical project.

    When and if you have it built, you should be able to have 1, then 2, then 3 automotive lights on this supply without it changing more than 0.1V. If the output voltage changes more than that and it is questionable. Figure on using 18 gauge wire where the current goes, if you decide to go with it we can fill you in with more info later.

    3 amps sounds small, but it isn't trivial. It will generate quite a bit of heat.

    If you build one of these suckers and it seems portable, you might be able to add some simple parts to the original wall wart to allow it to work.

    My main advice is, don't connect this to the laptop until you are absolutely sure it works. If it works you're a hero, if if smokes, well, nuff said.

    There are other ways of doing this, this was the result of about 15 minutes of searching.
     
    Last edited: Aug 19, 2009
  17. tng80

    Thread Starter New Member

    Aug 18, 2009
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    I'm game for that, just need to figure out the details I guess. I've got an extra pc psu or two lying around so that won't be a problem. Thanks Terry
     
  18. tng80

    Thread Starter New Member

    Aug 18, 2009
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    Ok, the real adapter arrived today so no need to go any further. I may take a shot at it anyway for experience, but it's not a neccessity anymore. Thanks for all the help Terry
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    Actually, I'm going to make another run myself at the problem, as shown on the thread I pointed you to. The idea of a switching regulator appeals, and if I can get it to work with 11.7 Volts (car voltage with the motor turned off) work work well from the cigarette lighter. The problem is I'm very laid back, I always have several projects running at once, with one being the focus at any one time, so this could take a while.

    The current one is

    Submission, CMOS 555 Long Duration LED Flyback Flasher
     
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