How to estimate whether this fuse can handle power supply cold starts?

[cm64]

A power entry module/switch(which requires a fuse) will power this power supply. The power flow order is as follows:

Fused power entry module/switch --> Wires --> Power supply

I know that a fuse is used for wires but in this case I have a 3A fuse needed for the power entry module with these curves.

As you see from the supply datasheet, the nominal power supply input current is 1.6A, but the power supply inrush current is given as 45A.

I have the 3A fuse so it must be fine for 1.6A. But the supply also has inrush current 45A. So can this fuse handle 45A?
(Supply datasheet doesn't provide the duration of inrush currents)

 

[KlausST]

Hi,

sadly I can´t help with the fuse.

May I ask you why you want to install a fuse? I mean the powersupply protects itself by overcurrent limitation and overtemperature shutdown. So it´s rather unlikely that an external fuse ever will trip.

Klaus

 

[cm64]

Hi,

sadly I can´t help with the fuse.

May I ask you why you want to install a fuse? I mean the powersupply protects itself by overcurrent limitation and overtemperature shutdown. So it´s rather unlikely that an external fuse ever will trip.

Klaus

I have to install a fuse otherwise the power entry module will not let the power pass to psu. It is embedded in enclosure so I cannot change that. It is the power entry module/switch which requires fuse. I could insert a 10A fuse but I have 3A with the datasheet I provided. The power supply can have 45A inrush current(duration not given).

So my question can this 3A fuse handle 45A current for 100ms? (I guess inrush current wouldn't me longer than that for the psu)

 

[KlausST]

Hi,

use the graph for the fuse.
choose the 3A line
follow it down to 0.1s.
check the according current.

This is the average trip time / trip current.

I´d say it´s about 45A. So it may trip or not. It´s just at the edge.

Klaus

 

[cm64]

Hi,

use the graph for the fuse.
choose the 3A line
follow it down to 0.1s.
check the according current.

This is the average trip time / trip current.

I´d say it´s about 45A. So it may trip or not. It´s just at the edge.

Klaus

Thanks I wanted to be sure if I interpret correctly. Better I wait and find 4A.

 

[wwfeldman]

the overcurrent protection is likely on the output, not necessarily on input

i would think that since they expect about 45A inrush, (if turn on happens
to be at maximum voltage and input capacitors are fully discharged),
that it can handle that inrush reliably long term

so its likely your 3A fuse will do

it isn't clear is you need a specific form factor for the fuse
a search at digikey yielded 77 littlefuse varieties with 4A or 5A and 250 or 300 VAC ratings
maybe one of those will help

i did not look for trip current vs time

 

[Velkarn]

So can this fuse handle 45A?

what to do:
1 measure inrush current shape
2 calculate I²t of this pulse using this guide
3 compare calculated value with I²t value of fuse from datasheet

 

[Easy peasy]

For the 3A fuse the I^2T given is 129.5 A^2.sec, the inrush pulse will be for an half cycle so 10mS for 50Hz, let us say 20mS to be generous ( conservative ) dividing the two figures and taking the square root gives a flat topped current pulse of 80 A for the 20mS

so it is likely the fuse will survive if the turn on starts from cold every time

Choosing a slightly bigger fuse is not a bad idea - e.g. 4A or 5A as this avoids nuisance blowing.