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Build a 24 Volt AC to DC Awning Retraction Transformer

written by: Swagatam • edited by: Lamar Stonecypher • updated: 2/27/2011

Found an old TV transformer in your electronic junk box and thinking of building a 24 volt AC to DC 20 amp transformer? Just add some diodes, filter capacitor, LED, mains cord, etc. - join them- and your homemade converter is ready to use.

  • slide 1 of 4

    Before we discuss a 24 volt AC to DC 20 amp transformer unit and its wiring details, it will be important for us to become aware of a couple of things regarding the subject.

    Firstly, here the word “transformer" relates to “conversion" and not the usual step-down transformer (though we’ll also be needing that here) and secondly the rated current of 20 amp as referred to in the title or any rating for that matter can be actually quite irrelevant, simply because the current rating will depend on the wattage of the connected load and will need to be selected accordingly.

    For example suppose you need a bottle of water and have two water ponds nearby, one a little bigger and the other being relatively smaller, so it won’t actually bother you where you dipped the bottle as both the sources will be able to comfortably supply you with your need of a bottle of water.

    The analogy is exactly comparable with currents in electrical systems. If we assume the maximum current requirement of the connected load to be well over 10 Amps, then probably we would require a 20 Amp input, to be on the safer side, however if the need is under 5 amps then the above selection would be a total waste of money and space as the excess capacity would never come into play practically.

    Another important factor worth remembering with current ratings is that, you can never connect a load that may consume current almost near to the rated input value, because since the accompanied voltage is directly proportional to the strength of the current would drop it to almost zero in the above case, turning everything RED HOT. The rule of thumb is to keep the maximum current consumption below 50% of the input rating for safe operations.

    Let’s return to the proposed design and see how we can construct a 24 volt AC to DC 20 amp transformer in the following section.

  • slide 2 of 4

    Transformers vs. Converters

    To construct a 24 volt AC to DC converter you will require the following very basic electronic parts and should be able to finish the assembly within minutes:

    A Step-Down Transformer with Current rating as discussed in the previous section, having a secondary winding of 0-24 volt and the input primary winding depending on the country specifications.

    Four diodes with ratings again depending upon the load (we’ll discuss it in the following content),

    A Filter capacitor whose value (µF) may not be critical, a 1000 µF is well enough, however the voltage is critical, which should be always double the input supply voltage, so you may select it as 50,

    A red LED and a current limiting resistor (4.7K, 1/4 W),

    A suitable cabinet to hold the above components secured inside an enclosure.

  • slide 3 of 4

    Construction Clues

    24 volt ac to dc 20 amp transformer connection diagram, image, picture  

    Wiring up the above devices is very easy and may be done with the following steps:

    The first step includes assembling the four diodes as a bridge rectifier. This can be done by connecting them as shown in the diagram over a piece of general PCB or simply by twisting the leads together maintaining the polarities appropriately. A more graphical presentation is given HERE.

    The type of diode selection will depend upon the load, if it’s below 0.5 amps you may go for 1N4007 diodes, with current above 2 amps 1N5408 will suffice and with consumptions exceeding this level will need selecting the diodes directly as per the consumed current.

    Next, the procured capacitor may be connected to the bridge as per the diagram, again polarity orientation will need attention- an opposite connection may result in a big explosion or damage to the capacitor.

    An optional LED/resistor indicator assembly may also be soldered across the capacitor.

    After finishing the above assemblies, now it’s just a matter of connecting it to the secondary output wires of the transformer.

    Finally, the transformer primary winding will need to be terminated out through a mains cord so that it may be plugged in for the required conversion.

    Once plugged-in the LED should instantly come ON and the desired output of 24 volt DC becomes available across the capacitor which may be used for the required applications.

  • slide 4 of 4

    Application Hints

    24 volt ac to dc 20 amp Converter Connection Diagram, Image, Picture  

    One application of the circuit above would be to use it to replace a costly 24 volt AC to DC 20 Amp transformer, or more accurately, power converter, for applications such as activation motors for retractable awnings. The transformer can also be used in homes, offices, campers, and during outings and picnics. Indoors, the unit may be simply powered from your wall socket carrying a 110 V AC outlet, which is applied to the primary of the transformer as discussed above and the received 24 volt DC output may be used as per one's needs.

    Outdoors this circuit can especially become very handy and may be used either with the existing alternator of your camper/trailer or from a diesel generator. Here, the circuit becomes sleeker and lighter weight as the bulky step-down transformer is not required and may be completely eliminated.

    The 24 volt AC input from an alternator is directly integrated to the points where previously the step-down transformer’s secondary was connected i.e. across the bridge rectifier inputs.

    The converted 24 volt DC output from the unit may either be used for charging an inverter battery or simply with the relevant appliances which require a 24 volt input power for their operation.