Had an interesting problem today which was resolved when we discovered three control fuses all with a resistance of aprox 14 ohms. I've never seen this before and certainly not with three of them. Is this particularly unusual and why 14 ohms? They were 50mA 20mm fuses
Regards, Bob
discovered three
never seen this
particularly unusual
its a function of the voltage and current flow characteristics of your meter in relation to these very low amperage fuses. The meter is moving enough current though the fuse in test mode to show 14 ohms resistance. something you dont see in high VA rated fuses.
If you had a fuse with a fine enough element you could blow it out with your meter current.
Phil Scott
But a new fuse of exactly the same type shows negligable resistance.
Are they 'surge suppression' fuses?
Newsey
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resistance.
That would speak to wear on the fuse element with use then..similar to how a light bulb element burns out..(they put reactants in the bulb to insure the element doesnt last too long ..but not in china in case you are interested).
with a fuse element the reactant is oxygen if it the fuse is hermetically sealed.
The successful way of looking at these things is that its never magic...its always physics... so you ask yourself what the physics are that would result in these outcomes.
Phil Scott
Thanks for the info Phil. It certainly gave us a diagnostic problem as the blown fuse led's were not lit but the analogue module went haywire.
How about posting a pic.
Newsey
Hmmm, that's odd..
I just looked through my Littelfuse catalog and the first two .050 ampere fuses I came across have a rated resistance of 11.3 ohms. Are you sure the replacements are the correct type? Exactly what is the model number of the replacements? What is "negligible?"
A fuse needs resistance, that is the means by which it converts current to heat, which is the mechanism responsible for "blowing." What kind of milliampere-level circuit do you have that can't tolerate a 0.7 volt drop across the fuse?
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