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.