AC Fuse Sizing

[atxguitarist]

I am wiring up a G540 and Keling 48v/7.3A power supply and need to know what size fuse to use between the plug and power supply. I have 3 KL23H2100 3.5A motors connected.

My thinking is that the power supply will consume up to 2.92A @ 120v of AC current, and I would need a 3A fuse. I came to this because 48v X 7.3A = 350.4 Watts for power supply output. To get AC input I divide that 350.4W by 120v and get 2.92A.

Is my thinking flawed? This is coming from the AP physics I took back in high school.

Thanks,
Jessie

[atxguitarist]

Well I took the advice of a friend and just tested small to large fast acting fuses. The 2A and 2.5A blew out with in a seconds. But the 3A fuse is holding after testing all 3 motors.

[Al_The_Man]

On a power supply primary it is normal to use slo acting fuses, this prevents the transformer inrush from nuisance blowing of the fuse.
Fast acting in the primary will not act fast for the secondary load anyway, as there is a delay through the transformer when a fault occurs.
Al.