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Is this built in fuse on pcb or what?

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Clarkdale44

Member
Hello

Is this fuse of some sort? or just an empty space for installing pcb based fuse socket?




This is the circuit board of my new cheap dmm, my last one broke when i mistakenly inserted the leads in mains while the red lead was in 10A socket. I just thought if there was a fuse inside the damn thing, it might have not blown up. I bought a new dmm, same as last one, and opened it up. There is a space for fuse, i just don't understand whether it is an on-board fuse built into pcb or is it just empty space for installing new fuse.

If it's an empty space for new fuse then what should be the fuse rating? so i won't make the same mistake twice!

Regards!!
 
Last edited:

JimB

Super Moderator
Most Helpful Member
This is the circuit board of my new cheap dmm
You nailed it right there!

Look at the narrowing of the circuit board track above the word FUSE. That narrow track is the fuse.
So next time you get it wrong and blow the fuse, if the circuit board is not carbonised at the same time, you can solder a suitable fuse between the two pads.

JimB
 

canadaelk

Active Member
This is a built-in fuse. Look at the trace on top of and connecting the 2 pads. The narrowing of the trace is the fusing part. The pads are there for you to install a 5x20 mm fuse in case you blow the trace. E
 

chemelec

Well-Known Member
YES, SORT OF.
They have a Tiny Jumper to somewhat act as a Fuse.
They can also Break that Jumper and Actually put in Fuse Clips and a Proper fuse
 

Clarkdale44

Member
Thanks for reply, but the funny thing is my last dmm also had this sort of fuse in the pcb, but it failed to blow resulting in my dmm blown instead. So should i just solder the new proper fuse? And what should be it's rating?
 
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shortbus=

Well-Known Member
Most Helpful Member
Probably allows the company to make two DMMs from one board. the low price one you have and a higher priced one with a fuse ,by breaking the thin "fuse track" and adding the fuse holder.
 

chemelec

Well-Known Member
Break that Trace and Put in fuse Clips and a QUICK BLOW, 500 mA Fuse,
 

Diver300

Well-Known Member
Most Helpful Member
The narrow track would blow quite predictably with a suitable over-current. I once had some boards with a 0.01" track that had to be removed, and it was quite easy to blow it with a 20 A power supply.

The problem comes when you have a serious over-current, and 10 kA is flowing. You then need a sand filled ceramic fuse. A circuit board will just arc across the gap. A glass fuse is better, then a ceramic fuse, and then a sand filled one, generally.

Good meters often have very expensive fuses, to handle huge over currents. http://uk.farnell.com/siba/5019906-11/fuse-for-dmm-1000vac-dc-10x38/dp/1827168 as an example.
 

chemelec

Well-Known Member
Base on the PCB, and the 250 Volt Fuse Rating I assume this is being used on a 110 or 220 VAC Line?
 
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