Unknown voltage ac or dc?

Discussion in 'General Electronics Chat' started by Derrick_weedman, Nov 14, 2010.

  1. Derrick_weedman

    Thread Starter New Member

    Nov 14, 2010
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    Put together a bridge rectifier (4 diodes) and pluged it into the wall, thought hey just put a voltmeter up to it to see if it changed the 110vac to dc. Tested it on ac first and it read 220v, wery of switching it to dc and frying my meter I am waiting your input.

    Thanks-
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    What kind of meter?
     
  3. Derrick_weedman

    Thread Starter New Member

    Nov 14, 2010
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    meter is a Greenlee test instrument Cat.No PDMM-10
     
  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Umm don't be playing with the mains. Why are you doing this?
     
  5. Derrick_weedman

    Thread Starter New Member

    Nov 14, 2010
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    ? no I dea what you mean
     
  6. Derrick_weedman

    Thread Starter New Member

    Nov 14, 2010
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    Need a power source for a 555 timer circuit so it doesnt need to be extreamly smoth dc like you would get out of a phone charger, cause every one probably has about 5 of them laying around. Wanted something simple most important small, bridge rectifier/ transformer resisters to lower voltage a little more and one or two caps about 47uf to smoth it a bit. if it blows up Im out two bucks. Not playing cards with the meter

    help?
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Playing around with an outlet is an excellent way to get a lethal shock. Always use a transformer to lower the voltage and get isolation from the mains.

    Probably the least expensive way to go is to get a wall transformer with a DC output. Any voltage from 10 - 15 should be good. Get one rated for 100 ma or so to give enough capability to run some LEDs and such.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Where did you get the idea the 555 doesn't need clean DC? While it might work with dirty power this is not a valid assumption.

    A simple wall wart is cheap, easy, and produces decent DC. Why handicap your self with poison power when the good stuff is easy?

    You will probably spend as much on the wall wart as you did the bridge rectifier.
     
  9. Derrick_weedman

    Thread Starter New Member

    Nov 14, 2010
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    Have been ripping all componets out of the trash stuffs that broken or has just been discarded not one red cent into it trying to keep it that way. If not I would go blow 50 bucks at radio shack and be stuck with something that ends up in the trash anyway.
     
  10. iONic

    AAC Fanatic!

    Nov 16, 2007
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    So you mentioned that you could use a transformer to knock the voltage down a bit. Why aren't you starting with the transformer, then to the Bridge rectifier. Rectifying 110VAC to DC is really, really bad news, way more leathal. Seems funny you are worried about some cheap old meter that you can make up for in a days work. I'd be more worried about your own tail end!

    iONic
     
  11. mbohuntr

    Active Member

    Apr 6, 2009
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    A 555 doesn't need much power, Go to Radio Shack, pick up the chip, and ask the "tech" to get you a suitable wall wart. Be safe.....
     
  12. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Be careful to buy a regulated wall wart.
     
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    The smallest ~5V power source you will find is typically a cell phone charger, or a 110VAC to USB port SMPS. They are extremely tiny these days, and pretty much everywhere due to how often manufacturers change the charging jack/power/etc.

    Find one that is the voltage you want, chop off the jack, check the wire polarities and use it.
     
  14. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Forget Radio Shack -- just go to a thrift store. They usually have a box of used wall warts for 50 cents or a buck apiece. Just read the labels to find what you need.
     
  15. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    or just drive around the block on garbage day, amazing the amount of electronics that get thrown out.
     
  16. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I am really surprised to see how u guys responded. :eek:

    OP said he just put 4 diodes and stick into the wall. And he got 220VAC.
    Non of u were serious enuf to tell him tht if he were to touch the bridge, he might as well end up in the graveyard.

    I dunno how he got the 220V. A bridge with an input of 110VAC with a cap will give you 155VDC. Here he does not have a cap. But if he were to connect any not knowing the voltage, this time he will end up with a big bang....

    Either ur meter is not good or u seriously dunno what you are dealing with.
    Any one with a good mind will NEVER stick a bridge into a mains to power a 555.

    Either you get a wall wart transformer or quit doing what u are at before u kill ur self

    By the way MODs....I think this is a serious issue when new members deal with new members. Either one doesn't realize what they are dealing with. I suggest Admin to take this into consideration
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    Riff, I'm not sure you read the same thread I did, the warning about direct mains has been repeated multiple times. Generally the thread just gets closed when someone proposes such a thing, but instead we focused on the safe way to do it.

    To the OP:

    Trying to use only junk box part is OK as it goes, when I was a teen I did the same thing. Even then I had the sense to make a safe power supply using a transformer though, even though it cost me money to do so. The currents and voltages you are messing with are no joke, and they could easily hurt or kill someone other than you.

    Making a variable power supply is pretty simple, but the first step is safe DC. Unless you throw them away with the appliance the odds are pretty good you have an orphan wall wart kicking around. There is a very good reason they are so common.
     
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