Chossing the proper fuse

[tutzeroone]

Hi everyone,

I've got a desktop lamp that looks roughly like this .

The base contains a power switch, a fuse and a cheap 220V > 12V transformer and the arms of this thing are acutally used to carry the current from the transformer to the lamp.

The fuse is rated 250V 6.3A while the bulb is supposed to be a 12V 35W unit, so I was wondering is 6.3A for the fuse wasn't too much and possibly unsafe.

I actually went a bit rough on the lamp and shorted the arms, the fuse blew but it took approx. 3s which seems "long" for a safety feature.

What do you think about it ? Should I use a 6.3A fuse or one with a lower value ?
Thanks in advance for your help.

[MK14]

Hi everyone,

I've got a desktop lamp that looks roughly like this .

The base contains a power switch, a fuse and a cheap 220V > 12V transformer and the arms of this thing are acutally used to carry the current from the transformer to the lamp.

The fuse is rated 250V 6.3A while the bulb is supposed to be a 12V 35W unit, so I was wondering is 6.3A for the fuse wasn't too much and possibly unsafe.

I actually went a bit rough on the lamp and shorted the arms, the fuse blew but it took approx. 3s which seems "long" for a safety feature.

What do you think about it ? Should I use a 6.3A fuse or one with a lower value ?
Thanks in advance for your help.

Can I check my understanding.

Is the fuse on the mains side (115V/230V) or on the 12V side ?

12V x 6.3A = 75.6W

On startup from cold, as a rule of thumb bulbs (filament ones), use something like x10 the usual current (briefly because the bulbs resistance is considerably lower, when cold).

So it could be about right ?

Also the fuse's 250V (as I assume you realize), is only a rating (its maximum safe voltage). NOT anything to do with the wattage.

Because Wattage = Actual Voltage x Actual current

[Brumby]

This is the question that must be resolved for any clear answer...

Is the fuse on the mains side (115V/230V) or on the 12V side ?

[tutzeroone]

Thanks for your answers MK14 and Brumby, I just checked and the fuse is on the 12V side, I thought it was on the mains side (220/230V here) which seemed odd.
But after what you explained MK14 it seems to be fine ! I didn't knew thoses bulbs had that kind of behaviour, thanks for explaining it ! The 6.3A fuse should be right so. Thanks for your help !

[MK14]

Thanks for your answers MK14 and Brumby, I just checked and the fuse is on the 12V side, I thought it was on the mains side (220/230V here) which seemed odd.
But after what you explained MK14 it seems to be fine ! I didn't knew thoses bulbs had that kind of behaviour, thanks for explaining it ! The 6.3A fuse should be right so. Thanks for your help !

You're Welcome!
yes, filament bulbs resistance is rather odd.
It's an easy mistake to make.