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RE: Zerozone 100VA PSU Fuse Issue

P = I X E

P = watts, VA (Volt Amps)
I = amps
E = volts

Here we have a 100VA transformer. Manufacture spec 115Vac primary, 12Vac secondary.

Find the max available current, in amps, the secondary winding can safely deliver.
(Note: The max amp rating is determined by the wire gauge that was used to wind the secondary winding)

100VA / 12Vac = 8.33 amps. So the gauge of wire used must be rated for at least 8.33 amps.

So how much current, amps, would the primary winding draw from the mains power if the secondary winding connected load is drawing 8.33 amps?

100VA / 115Vac (mains voltage) = 0.87 amps @ 115Vac. (Slightly higher due to losses)
(The wire gauge used to wind the primary winding must be rated to handle 0.87 amps minimum.

If you had access to the transformer manufacture's data sheet for the transformer you would probably see Maximum Rated Primary current 0.87 amps at 115Vac. Maximum Rated Secondary current 8.33 amps at 12Vac

The manufacture supplied AC Line fuse is a 1.6 amps (slow blow) fuse. More than big enough to handle a continuous load of 0.87 amps of current the primary is drawing to supply 8.33 amps on the secondary needed for the connected load.

I am not sure why the 1.6 amp fuse is blowing with only a 3 amp connected load on the DC output of the power supply. One thing you might try is to install a temporary fuse in series with the DC connected load of say 4 or 5 amps. If the AC line 1.6 amp fuse still blows then there is something wrong with the power supply. If the fuse blows that is connected in series with the DC load then the problem is there.

By the why, what is the 3 amp connected load?

EDIT:
What is the AC mains voltage the power Supply is plugged into?

Check the secondary AC winding voltage. What does it measure?
Measure with DC load connected.


Edits: 07/23/17 07/23/17
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