Voltage And Regulators

Discussion in 'The Projects Forum' started by ElectronicLife, Jul 19, 2014.

  1. ElectronicLife

    Thread Starter New Member

    Jul 19, 2014
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    Hi guys ...

    I have a question on voltage division :

    I have an 24 volts | 5 AMPS adapter and I want to divide it into 2 similar 12 volts | 2.5 AMPS channel. I know that I should use regulators or resistors to reduce the voltage or amps , but as far as I know this is DC power. It means when I put some resistors or regulators (like LM317T which gives alternative output voltage and more than 1.2 AMPS) , the power drains (these electrical parts consume the rest of power) and I can not make two similar power channel (12 volts and 2.5 amps).

    By the way , I can not use series connection due to some features of my projects!

    Please help me out!

    Thanks in advance ....
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,501
    380
    hi,
    For efficiency I would consider using a switch mode PSU to convert the 24Vdc to 2 * 12Vdc, you will not get 100% conversion, so the 5Amp will be down by approx 5% to 10%.

    Using linear regs, for 24Vdc to 12V, will be VERY inefficient
    E
     
    Last edited: Jul 19, 2014
  3. ElectronicLife

    Thread Starter New Member

    Jul 19, 2014
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    0
    I have found STEP-DOWN DC-DC which seems to be a great convertor for me! Can I use this to do so ?!

    And again the same question : Do I have to use 2 of STEP-DOWN DC-DC?! Can I use one of them for one of my channels and then the rest of the adapter power for the next one ?!

    More details of STEP-DOWN DC-DC Module :

    Input Voltage : 3-30
    Output Voltage : 1.28-18
    Output Amps : 2-3
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,501
    380
    hi,
    I assume the step down is a SMPS unit.?
    You can drive two SMPS units from a common 24Vdc source, just pay attention to the common 0V rails.
    Some SMPS are isolated from Input to Output, some are not.
    Do you have a d/s you could post for the Step Down unit.?

    E
     
  5. ElectronicLife

    Thread Starter New Member

    Jul 19, 2014
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    Here is a picture of STEP-DOWN DC-DC :

    [​IMG]

    It is adjustable for output parameters.

    I want to ask my question in another way :

    How can I power up 2 DC 12 volts fans separately with one 24 volts adapter?! I have 2 choices between Series and Parallel connection :

    I can't use series because : If one of the fans is off ,then the next one is off too!
    I can't use parallel because :
    If both the fans are on , then everything is OK . But when one of the fans is off , then the whole 24 volts come to one of the fans and it burns out!
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,779
    1,103
    How much current does each fan actually draw? (The label should indicate its power or current rating).
     
  7. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,501
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    With two separate 12Vdc 2.5A SMPS driving two separate 12Vdc 2.5A fans, connected to the same 24Vdc source, how will that cause a burn out.???
     
  8. ElectronicLife

    Thread Starter New Member

    Jul 19, 2014
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    Each of the fans needs 12 volts , around 2.5 amps.

    I know that when i use SMPS , there is no problem doing it and there is no burning out! (I was just talking about different types of connections). But is there any way to do such a thing without modules or SMPS ?! Because it is not economical to buy 2 of SMPS for this simple project !!!

    I have heard something about using low voltage regulators like 7805 and some diodes to power it up...

    Do you know anything about that ?!

    Thanks
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I doubt it will be any more economical to do it with a 7812 or similar linear regulator. With a 2.5A load the regulator, or other voltage dropper, will have to dissipate (24-12) x 2.5 = 30 Watts !! That will require the use of an expensive heatsink.
    The cheapest option might be to buy one 12V, >=5A power supply which could power both fans.
     
    ElectronicLife likes this.
  10. ElectronicLife

    Thread Starter New Member

    Jul 19, 2014
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    Do you mean to wire them up in Parallel connection ?! Because in parallel , the voltage of both the fans are the same and the amperage is sum of both of the fans (so it means 2.5 for each of them). Right ?!

    But I think in the real world , the voltage of adapter drains when you have already attached one of the fans to it !

    But anyway , Thanks for your guidance ...
     
    Last edited: Jul 19, 2014
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Correct.
    There should be very little voltage drop with a good quality adapter used within its specified operating limits.
     
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