24vac to 12vdc

Discussion in 'General Electronics Chat' started by kelvinmead, Dec 12, 2011.

  1. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    hi,

    i have a 6 channel 24vac transformer (4amp) and i wish to drive some 12vdc micro mag locks, 12vdc, 200mA

    quite simples, but not sure on the best way to complete.

    I've tried a full wave rectifier using 1n4007 diodes and a 0.01uF (103) capacitor

    but all it seems to do is blow the internal fuse on the transformer.

    :mad:
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    You really need to post a schematic of what you are trying to do. What do you mean by a 6 channel 24Vac transformer?
    I could make a couple of comments anyway:

    1. Rectifying 24V AC and smoothing it (with a big enough capacitor) will give something like 32V DC
    2. At normal mains frequencies, (50Hz or 60Hz) you would need something more like 1000μF smoothing capacitance. 0.01μF is far too small.
     
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    I have the same question. What is a 6 channel transformer. Never heard of that one.
     
  4. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    its stolen from coca cola!

    they are used for barlights.
    plugs into the 240v main and has 6 separate connections for 24vac outputs.

    so can i use a linear regulator with heat sink to drop from the 32v to 12v then?
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Sure but would be pretty inefficient and produce a lot of heat. But what is pfc?
     
  6. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    open to ideas then!

    what IS pfc?
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Well, PFC often stands for Power Factor Correction.

    It has to be said, the power factor of a biggish transformer driving a small rectifier load is going to be pretty poor, but why would you be worrying about that?
     
  8. K7GUH

    Member

    Jan 28, 2011
    191
    23
    This may sound a wee bit empty-headed, but what do I have to lose, eh? First, I sincerely hope you are using only one "channel" of the transformer output. Try your 1N4004 bridge with 1000 Mf across that to see if you do in fact get 32 volts without blowing the fuse. Then try a 100 ohm 2 watt resistor in series with the relay to see if it will operate properly. Don't leave it hooked up this way unless you can deal with a warm / hot resistor. If that all works, try a higher wattage resistor. But don't say I recommended this, I merely pointed it out. Otherwise, use a transformer that puts out something closer to 12 v.a.c. I do recommend that.
     
  9. Adjuster

    Well-Known Member

    Dec 26, 2010
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    300
    If you live in an area that has 120V mains as an option, you might try running the transformer on that to reduce its outputs to around 12V AC (about 15V rectified), unless you need the full 24V AC for other purposes.
     
  10. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Probably the easiest and safest option though is to get a commercial 12V DC adaptor. Unless you have a lot of these 12V 200mA locks to drive, it's not going to be terribly expensive.
     
  11. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    its just that i have this one for free, and maplin knock them out at £10 - £20 a piece!

    and im just trying to expand my electrical knowledgebase (although if its unfeasible then ill just purchase some!)

    ahh well.
     
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