AC to multi DC conversion

Discussion in 'The Projects Forum' started by hamzahng, Mar 17, 2014.

  1. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    Hi all,

    I'm new here, I have a project which is about creating an automatic irrigation system. Im trying to Build a power circuit for my system without using a transformer. The situation is as follows:

    I have a 12V-(1 - 2)A DC Water Pump and a PIC16F877A microcontroller with an LCD a couple of multiplexers, an RTC and a bunch of sensors connected to it tha uses a 5VDC

    I want to connect them all to a single power wall socket. Can anyone help me out with this situation.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    No transformer no deal.

    Get a wall wart or build one with a transformer.
     
    GRNDPNDR likes this.
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    If you wanna do this find a transformer rated for your mains voltage and with a secodary rating of 9VAC rated @ 3 Amps.
    A bridge and filter cap will give you the 12VDC for ur motor and a 7805 reg will get you the 5V needed for the uC and the rest.
     
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  4. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    Thank you for your fast response R!f@@. But I dont thithey hat this is the only way ... I thought of A full wave rectifier but I dont know am not very confident about it. And also I dont think That phone chargers have transformers in them ... yet they give us 5VDC from 220V AC wall socket
     
  5. wayneh

    Expert

    Sep 9, 2010
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    You might consider repurposing a PSU from any old computer on its way to the recycling dump. They all put out a regulated 12V and 5V outputs, and likely plenty of capacity for your future plans.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    A computer PSU is an overkill but will work and failure would infidelity need another PSU

    A tx and a bridge with reg plus a couple of caps will be easy to put together and easily fixed u know
     
  7. R!f@@

    AAC Fanatic!

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    Or try to find an adapter with 12VDC 3 amp capacity.
    Find one and we can show you how to get 5V from it.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yes, phone chargers (laptop power supplies, wall warts for calculators, etc.) have fully isolated transformers in them with lots of international safety ratings and approvals. Nothing safer if you can find one with the output you need.

    DO NOT try to connect directly to the AC line with a rectifier.

    ak
     
  9. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    I really didnt want to use a transformer but it looks like the safest way is to use a transformer... thank you all for your replies ... another thing if I bought a 220 - 12 Step down transformer ... will I be able to draw 1 or 2 Amps fron it and at the same time pull a 5V DC with little current for the microcontroller and the other ICs? And if anyone has an idea on where I can buy a good transformer online I would really appreciate it.
     
  10. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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  11. wayneh

    Expert

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    By "transformer" do you mean an old-fashioned power supply (wall wart) that employs a transformer? A modern power supply does away with the big heavy transformer and uses a switch-mode-power-supply (SMPS). Think of those power bricks that laptop users carry. One of those might be a good option for you, although they tend to be more like 20V. I'm sure you could find a 12V SMPS with a little shopping. You could get your 5V off of the 12V supply.

    If your intention is to somehow do a mains-direct connection for your system, that's not a topic allowed for discussion here. See terms of service.
     
  12. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    what do you mean by mains-direct connection? just so we are clear
     
  13. R!f@@

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    direct connection to mains will result in life threatening situations.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    The mods might want to offer a better definition, but to me it's about isolation. With a transformer, nothing you can do on the secondary (low voltage, "safe") side will expose you to a lethal mains contact.

    The classic example of a forbidden topic is the kid that wants to light some LEDs without using a transformer to do it safely. Not allowed around here.
     
  15. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    Oh, well of course I want to do something that is isolated and safe since I will be working with water ...
     
  16. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    I found one at home but its a 12V 1.5Amp adapter ... so can you help me in drawing a 5v from it for the controlling circuit and at the same time drawing a 12v for the pump
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I asked for a 3 amp one cause u said ur motor takes 1 to 2 amps.

    I dunno about ur motor. So I am not sure what current it needs to start and keep running.

    I can or anyone here for that matter can show you how to make the regulators.

    Question is about ur motor. Care to show me a picture of the motor or it's labelled specs.

    I am not sure you would need a exactly 12V for your motor. But the specs may tell us a maximum allowable voltage to motor.

    We have to assume worst case. So we have to go for 2 Amps for the motor (per ur posting). So that 1.5A transformer will be overloaded and will heat up and burn in short time.

    I need more info on the motor to tell you a reliable option.

    Sorry. I mistook for 12VAC.

    So you have a 12VDC adapter. Here is a trick. Connector the adapter and measure it's output without anything connected to output.
    Now connect your motor separately ( ensure correct polarity). See whether the motor starts up properly. Now measure the DC output while the motor is running. You need to load the motor. Say if the motor is pumping water, you must have it mounted on the pump and it should be pumping water as per your requirements. This will ensure the motor is properly loaded. Loaded motor current and unloaded motor current will be different.
    An unloaded motor will run but might stall when loaded due insufficient power from the adapter.

    Post ur measurements and then we can be sure if that adapter will work in the long run.
    You would need a DMM or VOM to measure the DC voltages
     
    Last edited: Mar 18, 2014
  18. hamzahng

    Thread Starter New Member

    Mar 17, 2014
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    Sorry for the late reply ... but I just got the 220V AC to 12V 3-A Adapter as per your request... its night at the time of posting This reply, but I will test it in the morning tomorrow. And I will post my results to you here as attatchments. But can you also help me in how to use this adapter to feed the microcontroller and the other ICs and sensors with 5VDC with low current...


    Thank you so much for all of your help
     
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Is it 12VDC or 12VAC.
    What is the no load voltage of the Adapter, without motor ?
    What is the loaded voltage of the adapter , with loaded motor (only) running ( while pumping water )?
     
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