Tweakers' Asylum

RE: Zerozone 100VA PSU Fuse Issue

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This Post Has Been Edited by the Author

In Reply to: RE: Zerozone 100VA PSU Fuse Issue posted by Duster on July 25, 2017 at 15:29:49

BTW, in this thread, I mentioned a Zerozone 50VA PSU with a 3A output that features a 5A 250V 5mm x 20mm fast blow glass fuse. How do you do the math for that one, Jim?

The wrong size fuse.

50VA / 120V = 0.42 amps.
(50VA / 115Vac = 0.43 amps)

0.42 amps X 125% = 0.53 amps (Just a guess the fuse probably was supposed to a .5 amp, 1/2 amp, slow blow fuse)

0.42 amps X 150% = 0.63 amps

0.42 amps X 200% = 0.84 amps

***** 0.42 amps X 1200% = 5.04 amps YIKES! *****
120Vac X 5 amps = 600VA

>>>>>>>>>>>>>>>

Secondary side of transformer,
50VA / 12Vac = 4.2 amp max output rating.

A 5 amp fuse will not protect the 50VA transformer from burning up in the event of a continuous overload beyond what the winding wire in the transformer is rated for. Yes the fast blow fuse probably would blow in the event of a dead short, but not a continuous overload. A 5 amp fuse will pass 4 amps all day long without breaking a sweat.
4 amps X 120Vac 480VA. You transformer is a 50VA.

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NOTE: The 1.6 amp fuse in the 100VA power supply is supposed to be a slow blow fuse, right?

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