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In Reply to: RE: Zerozone 100VA PSU Fuse Issue posted by Duster on July 18, 2017 at 22:01:56
12x6= 72 watts (VA) ? Not 100. It's possible that a fuse of 6A x 1.35 is considered safe in the EE World, or the next highest if needed. In this case an 8 amp fuse might be safe from a EE point of view. Anyone out there know for sure?? T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Follow Ups:
Assuming this is a voltage-regulated supply, you'd need to know the V developed before the regulators, in order to get an idea of the VA consumed and that is seen by the fuse.
It rated at 100VA. 100/12= 8.33 amps. Not 1.6A, not 3a and not even 6A. There is some wrong going on.
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
I could be wrong, but I think you are conflating two different quantities. The fuse is on the AC line going in. The size of the fuse has to be in relation to the AC power consumed, not the power that goes out to the equipment. Of this, I am sure. The fuse is seeing 120V coming in, so the divisor in your little equation is 120, not 12. Therefore also, the AC current consumed from the wall socket is way less than 8.33A, probably less than 1A. But we are still missing the bit of data that tells us what voltage is developed at the secondaries of the transformer. If the output is regulated (as I mentioned before) then the voltage at the secondaries has to be > 12V, maybe 15V or more for decent regulation. What I am not certain about is whether the 100VA rating refers to output or input power. The natural assumption is that it refers to output.
Edits: 07/19/17
Lew, wouldn't the max wattage (va) or the actual wattage be similar at the secondary and the primary?? UM's suggestion to actually measure what's going on, while it's a good suggestion, this issue should be dealt with correctly by the engineer of the product before they send these things out with fuses that don't make sense. Although fuse sizing can or maybe a bit complex in some situations it's still basically comes down to Ohm's Law with a certain amount of headroom from what I can tell. T456
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Actually I think this is correct. Basically what you said Lew. 100VA/120v=.8333. .833x 1.35= 1.12A for a reasonable rating for a primary fuse. It looks like it would have to be 6A rated at the secondary. So the numbers being thrown out of 1.6-3A fuses do not look correct. Pretty sure we are talking about a primary fuse. 1.6 is a bit high and a 3A should be out of the question if staying within conventional safety calculations. This seems to put Duster back in the hot seat in terms of the frequent blowing.
"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."
- Q, 2365
Edits: 07/19/17
100VA is being used as a marketing designation since it does not have an actual model number. The PSU features a 100VA toroidal transformer rather than the rated output of the PSU.
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