A I have a 230V/12V, 3A step-down transformer. What will happen at primary side of transformer if I attach a 12V/5A device at secondary side? Will primary side attributes (such as voltage or current) change?
I really am not sure what will happen on the primary side. But I can tell you that whatever you are powering on the secondary side won't get enough power to work properly for very long.
The primary will pull 261mA. more than likely, you won't see anything like voltage drop on the primary or secondary, but you will see (maybe) thermal stress on the transformer as you're exceeding it's VA rating. If you cool the unit properly, it could last indefinitely.
Primary side you will get 230V , nothing will happen to Transformer, you must be very care full do not touch the primary side just measure it with multimeter
the transformer converts Watts if it is rated at 12V 3A it means 36 Watts if you load-it more than that it will overheat and eventually burn the primary current is proportional to the secondary current however with an overload of 5 A as oppose to a load of 3 A it may last for several hours before becoming too hot the answer is yes you can run your load for a while provided that you monitor the temperature and watch the situation however do not load over 3 times the rating (8~9A) for any length of time more than 1 second A
