Fuse for 5V 1A

[merlin el mago]

How can calculate needed fuse for a PSU 5VDC 1A?

[madtecchy]

Wich fuse are you talking about.. The mains input fuse or the fuse on the output. what will you bee using the psu to power. what current does that draw.

Regards ian

[KatieandDad]

If it is the mains fuse, what mains voltage are you using ?

[merlin el mago]

Both. 230VAC.

Thanks Felipe

[AndrewT]

5VA mains fuse.
Try to find the lowest T rated mains fuses available. Try T100mA or T250mA.
1A secondary fuse. Don't. It needs to be so large to survive the first charge from cold of the smoothing capacitors that it offers virtually no safety purpose.
Instead fuse after the smoothing capacitors and rate the fuse to suit the worst case "normal operating condition". Not the 1Aac rating of the transformer.

[merlin el mago]

Thanks AndrewT, if I understood well only 100mA mains fuse, right?

[AndrewT]

Yes, T100mA mains fuse on a 220/240Vac mains system can supply ~23W continuously.
It will supply transient power of <=46W for many seconds and perhaps more than half a minute.
It will also supply short term transient power of 230W for a few milli-seconds, maybe even tens of milli-seconds.

A T250mA will take significantly longer to blow in event of a serious overload.

[merlin el mago]

Thanks for support, could you elaborate how can calculate for a future?

[AndrewT]

amps = VA / Mains voltage. It's the same formula as in P=IV

[KatieandDad]

Of course it also depends on what is connected to the secondaries of the transformer. Not so true for your low power application but certainly true as the transformers and their loads get bigger and more capacitive.

If the load is highly capacitive the instantaneous current might be much higher. If the 100 mA fuse blows try a Time Lag Fuse. This is more prevelant with Toroidal Transformers.