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RE: Zerozone 100VA PSU Fuse Issue

Posted by jea48 (A) on July 23, 2017 at 09:27:07

In Reply to: RE: Zerozone 100VA PSU Fuse Issue posted by Tweaker456 on July 22, 2017 at 21:52:58:

This seems to somewhat contradict some of the other info I've seen and heard that is quite a bit more conservative. Never saw this before. T456


Tweaker456,

I should have qualified my response, given in my previous post, is for transformers that fall under the jurisdiction of the NEC. Mains power AC line overcurrent protection of power transformers used in cord and plug connected electronic equipment may be different. Though I believe the max 250% of the manufacture's FLA ampere rating of a power transformer is probably safe. But that may not be the case.

Bottom line though, the designer, manufacture, of the equipment has the final say on what amperage fuse size and type of protection fuse he requires to be installed in his equipment. If the equipment is under warranty and the user installs a bigger fuse and or different type fuse and through an equipment internal failure, or caused by a connected overload, damage to the equipment may/will void the manufacture warranty.

In this case the 1.6 amp fuse is 200% of the 100VA rating, 0.83 amp FLA max rating,(for 120Vac mains) of the transformer used in the power supply.

NOTE: It seems the seller that sold Duster the Power Supply said he could use a fuse higher than the 1.6 amp supplied fuse up to a 3 amp fuse.

I read the eBay seller's add and he states the AC input voltage being 115Vac not 120Vac. I can only assume 115V is from that of the manufacture's spec of the power transformer.

100VA / 115Vac = 0.87 amps (max rated primary continuous duty amps)

300% X 0.87 = 2.6 amps @ 115Vac

100VA / 120Vac = 0.83 amps
300% x 0.83 amps = 2.49 amps
350% x 0.83 amps = 2.9 amps

Not sure I would use a 3 amp fuse to protect a 100VA transformer. I don't think an AC Line 3 amp fuse will protect the full wave rectifier or voltage regulator from a connected overload.
Jim

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