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Under-rated fuse question
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Siwastaja:

--- Quote from: Jester on March 29, 2019, 12:44:15 am ---I looked too quickly, was actually looking along the 340ma line (one column over on the graph), however the 160ma fuse yields a probably acceptable, trip time of about about 200s

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The curves are for "typical unit". They don't include unit-to-unit variation, which tends to be quite large. A proper datasheet should state the minimum current that guarantees a blown fuse in any time at all, and you'll see it's a larger value than what you see on this curve. This information is lacking from this cheap fuse. It's often 1.5x rated current, i.e., 240mA for your 160mA fuse, so if your load is actually 239mA, it's never guaranteed to work. Hence my recommendation for a 125mA fuse, but that could probably nuisance blow.
SteveyG:
Something like this would justify an electronic 'fuse'. Is this a possibility?
Ian.M:

--- Quote from: Neilm on March 28, 2019, 07:52:10 pm ---I have seen resistors that have a "pinger" on them. If the resistor gets too hot the pinger opens and disconnects the resistor. The downside for this is it is a single shot device and you would have to replace the whole resistor. Also they are not that available. A thermal fuse that is pressed up against the resistor would be a reasonable option

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I remember those. They used to be fairly common in really old TVs.   A square or rectangular section ceramic bodied axial resistor, mounted vertically, either had a springy steel strip in a T slot up the side of the body with the top bent over in a loop and soldered to the top resistor lead which was a short stub, or there was a formed steel sheet cage round the resistor body with a similar springy strip at the top end.  The steel was typically tin or copper plated for solderability.  The solder joint to the resistor lead was made with low melting point alloy, and if you had to repair it after it had disconnected, it was essential to use a freshly cleaned soldering iron bit with flux but no extra solder so you didn't significantly change the alloy composition.
Ice-Tea:
What's keeping you from putting a PTC in series?
Jester:

--- Quote from: Tomorokoshi on March 29, 2019, 04:21:59 am ---Is there anything special about 30W for 15 seconds? For instance, can you do 15W for 30 seconds?

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Special because it's in the specification, so no it has to be 30W for 15s
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