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Step down 240v AC to 24v AC

Discussion in 'General Electronics Discussion' started by Laywah, Apr 7, 2015.

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  1. Laywah


    Dec 19, 2014
    Hey everyone,
    I am seeking for a method to convert 240v AC to 24v AC so that I can perform several tasks using one Power supply.

    Generally i know that you should be able to use a step down transformer to do this, I am just having difficulty finding one to do the job.

    my power requirements are:
    1x 24v AC @ 1.5amp
    1x 5v DC @ 2amp (for a raspberry Pi)

    simply, I know that once i have 24v AC i can easily convert this to DC and then fine tune it to get the right voltage and amps for the Pi and likewise I can distribute the AC stuff out to the AC components.

    Does anyone know of a suitable transformer to do this or have another suggestion on how I can achieve what i need?
    If possible I would also like this to weigh less than 2Kg?
  2. ramussons


    Jun 10, 2014
    Is the "AC components" important?

    If not, then the simplest would be buy readily available 5 Volt and 24 V SMPS units.

    If you want to make the power supply, look for a 24 volt transformer with a 6 volt tapping. You can convert these to regulated DC as planned. 24-6-0-6-24 winding will be the secondary configuration for a full wave rectification followed by voltage regulators.

    Using a 0-6-24 secondary is not recommended since you can use only Half Wave Rectification leading to core magnetisation due to DC.

    You should not use Bridge Rectifiers UNLESS you have a separate 24 Volt and 6 Volt windings.

    You can feed AC to other "components" ONLY if you are using the underlined para above (there may be exceptions) since only this configuration will have a common "ground" for AC and DC power.
  3. Laywah


    Dec 19, 2014
    Thanks Ramussons,
    I am esesentially trying to build a retic system using a RPi.

    I am only focusing on the electronics at this stage and I need 24VAC @ 0.125amps to power each solenoids.

    For design reasons I want enough power to fire 6 solenoids plus a contactor which is about the same rating as the solenoids.

    I dont see the two separate power supplies being a solution as other retic controllers only have one cord.

    I dont understand the 24-6-0-6-24 and 6v tapping but if that meets my needs I am happy to go with that.
  4. Kiwi


    Jan 28, 2013
    Jaycar MM2012 is a 24vac 3A transformer for $28.
    Altronics M2190L is a 24vac 5A transformer for $38.
    Both these companies have branches around Australia.

    How many solenoids will you be running at the same time?
  5. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    You should buy a step-down transformer providing 24 VAC @ 2A (or more) to provide power for your solenoids and contactor.

    You should buy an inexpensive 5 VDC @ 2A switch-mode power supply to provide power for the Raspberry Pi.

    Forget about deriving DC from the step-down transformer. It's not worth the bother when for a few dollars you can purchase a cheap power supply for your modest current requirement.
    davenn likes this.
  6. davenn

    davenn Moderator

    Sep 5, 2009

    Yeah, that's actually a better way to go :)

  7. ramussons


    Jun 10, 2014
    It's a 24 Volt transformer with a Centre Tap and 6 Volt tappings like:

    Last edited: Apr 8, 2015
  8. Laywah


    Dec 19, 2014
    Thanks for all the explanation and suggestions with this. Hopefully I will be going to Jaycar or Altronics sometime in the next few days to get the transformer. Will put it together and see how things go. :)
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