Power Supply?

Question

I want to build a power supply to put out 12 V @ 1.0 A, and it will run off of 115 VAC.
My transformer is Primary 115VAC, secondary 24 VAC 2.0 A
My bridge rectifier 50 V 2 A
My Regulator 12 V 1.0 A

Q. I want to install a fuse from the main line to the transformer but I am not sure what size fuse I should use.

I am thinking:
My Primary is 115 sec. 24 so this is a factor of 4.79. This should mean that when i am drawing 1.0 amp on the secondary end, the primary will be drawing 4.79 less current. Is that correct?
If so then would I use a fuse rated less than .20 Amp??

Answer 1

The transformer will put out 24 watts, although only 12 of those will wind up in the output power. For 120 volts, that is only 0.2 amperes. I'd use a 1 amp fuse and call it good; a 0.5 amp fuse would be fine if you have one. The regulator will be dissipating 12 watts, so a good heat sink will be essential. I would have chosen a smaller transformer; 16 volts would have been ample. You will need a suitable capacitor, something on the order of 3500 microfarads would be suitable.

Answer 2

To supply 12V at 1A, you should need 0.1A at 120V. Plus losses and safety margins and fudge factors. The fuse is to protect the wiring and the circuitry on the primary side of the system, so if your wiring and the transformer can stand the current, I would use a 1 A fuse. Just a shirtsleeve guess on my part.

Answer 3

Use no less than a slow blow 0.1 amp fuse, 0.120 to 0.150 would be a better range. You might also want to consider using a self resetting fuse.

Answer 4

Fuse 1.9 a