Newbie here. Need some help

Discussion in 'General Electronics Chat' started by dezi, Aug 3, 2012.

  1. dezi

    Thread Starter New Member

    Aug 2, 2012
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    Hey everyone.. I am very new to electronics and assembly etc.. I have someone that is going to help me out but I need to find a transformer for a project I want to build... Here is what I need

    120V AC in

    12 & 24 volt both AC and DC out. Around 3 amp would be nice..

    Can you guys help a newbie out? What do I need and where can I find it in Canada.

    Thanks for the help. I am trying to learn and I plan to do a lot of looking around here.

    Thanks!

    Dezi
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Usually it helps to give us the big picture. What are you working on? This sounds rather complex. If it is an automotive project, then don't bother to tell us.

    12 & 24V AC and DC mean four supplies:

    12VAC
    12VDC
    24VAC
    24VDC

    Can you be more specific? Why do you need AC?

    A transformer outputs AC. You will need a DC power supply circuit (rectifiers, reservoir capacitor and voltage regulator) to provide DC output.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I agree with Mr Chips. It would help if you told us more about what you are planing to do. Not much to work on here. The more details the better
     
  4. SteveHow

    Member

    Jul 2, 2012
    78
    2
    Hello Mr Chips,

    if you don't mind me jumping this for a quick question. I see you have mentioned "Reservoir Capacitors". Are these also considered Smoothing Capacitors and if so, is it true they are performing 2 functions, i.e Current reserve when the load varies and also smoothing out AC Ripple? (I ask because I have never heard of anyone calling them Reservoir Capacitors before. Don't get me wrong I am not questioning just curious)

    Thanks
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Yeah, I don't usually call them "reservoir capacitors". I originally wrote "storage" and then changed the wording. Possible words are:

    filter
    smoothing
    storage
    reservoir

    The function of the capacitor in this application, whether filtering, smoothing or storing, is all the one and same.

    The voltage output after rectification is two halves of a sine wave with voltages from 0V to the max voltage. This is no good for most applications and we need to smooth the voltage to a steady voltage. The capacitor's function is to hold the voltage steady at an acceptable level while the half sine wave drops below this holding level.

    All the charge to the load has to come from the capacitor, hence it is a called a storage or reservoir capacitor.

    The simplest analogy is a water reservoir that has to maintain a constant output water pressure while a pump is trying to top-up the tank at intermittent intervals.
     
    SteveHow likes this.
  6. SteveHow

    Member

    Jul 2, 2012
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    2
    Love the analogy, awesome, thanks.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    A transformer with only two connections on the secondary windings will require four rectifiers (diodes) in what is known as a full-wave bridge.

    If the transformer secondary has a center-tap, then you need two rectifiers.
    Note that the voltage and current outputs are quite different.

    Reference (pdf):

    http://www.hammondmfg.com/pdf/5c007.pdf
     
  8. dezi

    Thread Starter New Member

    Aug 2, 2012
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    I am planing on making a etching machine... For my knives that I make and I need both AC and DC outputs. AC for the deep etch and DC for making it black..

    Sorry Everyone, I should have given more details....

    So what do you think would be best????

    Thanks

    Dezi
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    I don't know what is an etching machine and what knives have to do with it. Maybe someone else can explain.
     
  10. #12

    Expert

    Nov 30, 2010
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    Basically, we're not buying the idea that you need all those outputs to do some etching.

    I'm thinking: a Variac into a 24V, 3A transformer and a Radio Shack 12V power supply, which will also work with a variac, at least good enough for etching and plating. A couple of packs of 10 ohm, 10 watt resistors to limit the current and a calculator to do Ohm's Law on the resistors. Been there, done that, and these are what I used.
     
  11. cork_ie

    Member

    Oct 8, 2011
    348
    58
    Do You mean 12 V AC 3A, 12 V DC 3A, 24V AC 3A, 24V DC 3A ?

    That would be 12A total?

    The ideal would be to get an old 12/24 Battery charger and install 2 new rectifiers. 10A Bridge rectifiers are available for peanuts - less than a $ a piece. If the voltages are critical you could use an LM338 Regulator which is adjustable or alternatively something like a 2N3055 controlled by a voltage regulator on each DC output. This combination would easily be sufficient for your need with a wide margin.

    AC will be a little trickier and as previously mentioned a few heavy duty resistors and a bit of Ohms law should be OK in most cases. Look at your machine's specs and see what voltage range it will tolerate
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    I think he means something like this - http://www.etch-o-matic.com/knifemaker.htm We used them at work to mark parts we made.
     
  13. dezi

    Thread Starter New Member

    Aug 2, 2012
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    Yep thats what I am looking at making but I plan to add a few little extras to mine....

    Thanks

    Dezi
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    Why didn't you come out and say so in the first place instead of 12 posts later?

    What are your power requirements?

    AC or DC?
    Voltage?
    Current?
     
  15. dezi

    Thread Starter New Member

    Aug 2, 2012
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    0
    Need to switch from AC to DC 12 volt and 24 volt for both and 2 amps for both
     
  16. shortbus

    AAC Fanatic!

    Sep 30, 2009
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