Power supply fuse sizing question

[kevincnc]

I have a 24 VAC transformer, no other specs, about 5" square that I want to make an unregulated DC power supply with. (Bridge rectifier and capacitor)

Can anyone tell me how to properly size the primary and secondary fuses? Also what value and power rating for a bleed resistor?

[Al_The_Man]

If you want to be fairly close and you do not have the specs on the transformer, you could put a load on the secondary that will approximate you final total load, and monitor the primary current, and temperature. Then multiply this by between 1.5 & 2 times for fuse value, use slo-blow type.
If you fuse the secondary, I would put the fuse in the DC after the Capacitor, as currents can exist that peak at twice the rated VA of the transformer and can cause nuisance blowing.
The primary fuse will take care of any problem that may occur like a shorted rectifier etc, as any current is reflected back to the primary anyway. Fuse this DC to around 1.5 times your highest anticipated load current.
Al

[kevincnc]

Thanks Al,
It's hard to approximate the total load, it will be for servos so I want to be able to safely draw as much current as possible. I could put a load on it and increase it slowly until the transformer reached a certain temperature. What temperature would be acceptable?

[murphy625]

When in doubt, under-fuse it...

You can always go larger later on...

Murphy