Converting AC - DC Help

Discussion in 'General Electronics Chat' started by G4M8L3R08, May 18, 2015.

  1. G4M8L3R08

    Thread Starter Member

    Dec 27, 2014
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    Hi Guys,

    I have a small task to complete tomorrow, I have a 60vac output from a sounder, I need to use this to close a 12v dc circuit, a siren connected to a power supply.

    My idea was the circuit bellow, but to also throw in a led to show its working when the 60vac is applied.

    I also need this then to switch a relay that will close a 12v circuit.

    Hope you can help me in time. Thanks in advance
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    You're circuit looks about right - but without filling in the component values, its hard to predict how much of the magic smoke you'll let out.
     
    mattbullet likes this.
  3. G4M8L3R08

    Thread Starter Member

    Dec 27, 2014
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    Im going to use a KBPC601 bridge rectifier and a 2.2k resistor, think iv also got a pack of .5uf caps laying around.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    What are the specs for the relay you intend to use and what determines whether the relay should be energized?

    Seems like you'll need a regulator and a larger filter cap. What's the resistor for?
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    I'm not going to sit here and research the data sheet for you.

    You need to insert the values you've quoted so far into the Ohm's law equations and confirm that the rectifier can handle both the voltage and current, and that the resistor can dissipate the resulting power.

    For most practical applications, a 0.5uF capacitor will be too small - you could be in need of hundreds or even thousands of uF.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You don't need any cap as far as the relay is concerned, especially when a BEMF diode is use.
    Digikey have DC relays for 60vdc.
    With a large cap it would put it over 80vdc.
    Max.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    Any capacitor there will effectively turn it into a peak detector. Multiply VRMS by 1.414 and that's what you'll get.

    Although the peaks are still there - just not enough of the time for a DC meter to give an accurate reading.
     
  8. G4M8L3R08

    Thread Starter Member

    Dec 27, 2014
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    Ok scrap my idea, could someone please tell me how to achieve my goal please. I can purchase new parts in the morning from Maplin which is down the road from me.
    60v ac output, I need it to switch a relay that can close a 12v circuit.

    Im clearly not as smart as you guys with this lot
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is why I suggest no cap, not really needed in this case just to switch a relay and an indicator.
    Max.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Order a 60vdc relay and use the bridge you show, wire a reverse, (BEMF) diode across the relay, (Google if needed).
    Use a contact on the relay to switch the 12v, you will need a relay with suitable rated contacts for the 12v load.
    Or if you do not need the LED, use a 60vac coil relay if avail, and no bridge or BEMF diode.
    Max.
     
  11. dl324

    Distinguished Member

    Mar 30, 2015
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    You have yet to state your objective...
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    The TS is planning to use a 50V BR - so that could be the first thing to sort out.
     
  13. G4M8L3R08

    Thread Starter Member

    Dec 27, 2014
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    I have 2 wireless sounders that produces 60vac when they go off, one was smashed yesterday on the back of my lockup, I cant get one until next week so I am wanting to add a spare siren on the back to alert me should anyone have an attempt at breaking in. The last one thats working produces 60vac to the sounder, I would like to tap into this to trigger my spare siren (12v dc). I have a spare 12v psu to power it. Just need to link them together
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Good catch!
    Max.
     
  15. G4M8L3R08

    Thread Starter Member

    Dec 27, 2014
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    is anyone able to provide me with a parts list that I can pick up tomorrow from Maplin?
     
  16. ian field

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    Oct 27, 2012
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    I don't think you've given enough detail for any of us to design your circuit for you.
     
  17. dl324

    Distinguished Member

    Mar 30, 2015
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    I'd use an opto-isolator; LED driven by your rectified 60VAC. The transistor in the opto-isolator can drive another transistor/MOSFET that drives your relay coil.

    If you want to minimize component count, you could use the AC to drive the LED and put a reverse biased diode across the LED to protect it from reverse breakdown. Resistor, diode, opto-isolator, drive transistor, and relay.

    EDIT: Like this (replaced opto-isolator, drive transistor, and relay with a solid state relay):
    siren.jpg
     
    Last edited: May 18, 2015
  18. G4M8L3R08

    Thread Starter Member

    Dec 27, 2014
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    I cant find a solid state relay on Maplin website so im looking through the 4 opto isolators that they stock. I will get the bridge rectifier to power the opto isolator and go that way......
     
  19. dl324

    Distinguished Member

    Mar 30, 2015
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    You can drive the opto-isolator the same way as the solid state relay. You just need to add a transistor and relay; and probably a snubber diode.

    If you're siren doesn't like being switched on/off, you could go with the rectified, filtered AC.
     
  20. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    what powers the wireless sounders, internal batteries,if so why dont you tap off the trigger voltage that sets the sounder off..
     
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