I am working to make a power supply with Ups backup. Im still learning different things about making a power supply. However currently i am trying to chose an appropriate transformer size.
my load would be
1) 5v, 2A
2) 12v, 2A.
Some one told me that a transformer 220vac to 18vac rated at 3A would be more than enough. However when I used Isis protues to simulate the current being drawn, the ac current rose to above 4A on a 15v 2A lamp which equals 30W. The DC current being drawn was however 1.6A after being rectified which makes sense at around 18v it almost equals 30W.
Now i am confused on how big a transformer should i use.
Ive attached a jpeg of the simulation for reference.
Any sort of help is well appreciated so thank you in advance.