Fuse blown or not? Image attached

[tankman1989]

I've seen fuses shaped like this that have a wire running through them and I've seen pics of fuses like this (in catalogs) that are cloudy, so I guess this is normal.?

It looks like the only way to replace fuses like this is by unsoldering them. What a PITA! IS there a reason that they use these? Can I replace them with a more easily replaceable fuse holder or is that a problem?

 

[Krynn72]

Those are ceramic fuses, so yes thats what they're supposed to look like. I've replaced a couple fuses like that by desoldering them, and soldering a radioshack fuse holder. If you blow another fuse, the holder makes it super easy to swap out, it literally just snaps into the two ends.
http://www.radioshack.com/product/index.jsp?productId=2102786

As to why they use them, my guess would be that its just cheaper, as it can get wave soldered at the same time as everything else, instead of needing a person to snap them in along an assembly line.

 

[frase]

What is the board from, do you have number?

 

[tankman1989]

What is the board from, do you have number?

It is from a UPS and only has a very long SN. I can't see anything that may resemble a PN or board #.. There is space for a Rev# but it is blank.

 

[citizensmith]

A multimeter set to Ohms / resistance / continuity is a useful tool or at your own risk \ safety precuations - measure voltage across ie either side of it when live. If no volts then fuse is ok.

 

[Larry Sabo]

Fuses usually blow because of a short on the load side. Are you comfortable troubleshooting the components on the board, like MOSFETs, diodes, etc.? Simply replacing the fuse won't fix the reason it blew in the first place.

 

[mr m]

Great idea to solder a fuse holder to the board. Just make sure you replace the fuse with another ceramic model with the same specs. They are designed for high current/voltage use.

 

[phaZed]

A multimeter set to Ohms / resistance / continuity is a useful tool or at your own risk \ safety precuations - measure voltage across ie either side of it when live. If no volts then fuse is ok.

I think what you mean to say is (Correct me if I'm wrong), if no volts then it is safe to touch - if there is a very low resistance value then the fuse is good. If the fuse is open (infinite resistance) then it is bad.

But do be careful and unplug the thing... it could still be energized, the fuse could be blown in which case you would read Zero volts, but one side is still hot. Also, you should read a very small voltage on a fuse because when you measure each side of a device like that your really reading voltage drop, or the amount of voltage that the device is consuming. A fuse is going to be very low resistance, hence will read a very small voltage drop.

 

[Moltuae]

I think what you mean to say is (Correct me if I'm wrong), if no volts then it is safe to touch - if there is a very low resistance value then the fuse is good.

I understood him to mean no volts across the fuse when live -- which is correct. There's no significant volt-drop across a fuse, therefore there should be a PD of zero across it. It's not a 100% reliable way of testing a fuse, since further faults can lead to the same conclusion, so for that reason (and for reasons of safety), it's generally better to test it with the power removed whenever possible.

 

[phaZed]

I understood him to mean no volts across the fuse when live -- which is correct. There's no significant volt-drop across a fuse, therefore there should be a PD of zero across it.

Not to split hairs here, but if the fuse is NOT live you get zero volts too! Live, not live.. checking the voltage across the fuse is not how you want to do it .

Checking resistance on an unenergized circuit is the way to go!

 

[Moltuae]

Not to split hairs here, but if the fuse is NOT live you get zero volts too! Live, not live.. checking the voltage across the fuse is not how you want to do it .

Checking resistance on an unenergized circuit is the way to go!

Absolutely.

Although I would assume people would have the sense to check that there was voltage present relative to ground before checking the PD across the terminals.

I wasn't condoning that method of checking. Like I said, it's generally better to test it with the power removed whenever possible, it's neither reliable nor particularly safe not to; I was just clarifying what I assumed citizensmith meant.

Actually, to be totally pedantic, not only is it better to meter the fuse (or any component for that matter) with no power applied to it, the only real way to be 100% certain is to test it out of the circuit. Metering components in-circuit can lead to misleading results, though that problem applies less to low resistance devices like fuses.

 

[mr m]

X3 on testing the fuse out of the circuit with an Ohmeter.

It's rare but I've seen them break under the cap and not in the middle like they are designed to do.

 

[citizensmith]

Sometimes you need to fault find on Live gear - probabley not for this forum - just to clarify - measure volts across or on both sides to earth.
But in this case if you dont know if the circuit is Live or not - dont go messing a bout with it. Best go find a tech or do the funky SIDE thing;
Switch off
Isolate
Discharge
Earth
/Elfin Safey brief

 

[layoric]

How much to replace the whole unit? Why bother if it can be replaced for the same or less?