Do thermal fuses fail from old age?

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On Fri, 23 Mar 2012 12:48:47 -0700, "William Sommerwerck"

I don't really like the plastic head mounted magnifiers. I'm constantly going from whatever I'm working on, to picking up tools, soldering iron, parts, probes, etc, on the bench. I have to keep raising and lowering the magnifier in order to switch. With an LCD screen, everything is roughly the same distance away, so no raising or lowering.
If I were to buy a head mounted magnifier, it will probably be a surgical loupe. <https://www.google.com/search?q=surgical+loupe&tbm=isch Lots of styles and types to choose from, all seriously expensive. I've played with some and am rather impressed. If I can keep the working distance constant, it's as good or better than my USB camera microscope. Mounted on eyeglasses, they are a bit heavy, but headband mounts are available.
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Jeff Liebermann snipped-for-privacy@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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William Sommerwerck wrote:

Those things and drugstore reading glasses are great if you happen to have just the right interpupillary distance. I buy lab glasses from Zenni Optical for about $35 a pair--+0.75 diopter for reading, +2.5 for close work, coated, good frames, just the right interpupillary distance to avoid eyestrain. Highly recommended.
Cheers
Phil Hobbs
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Dr Philip C D Hobbs
Principal Consultant
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The larger resettable switch type are usually rated as combined (self-heating) current and thermal cutout. Maybe similar for "Woods" metal types , say if in circuit with fast switching on and off thermostat or poor contacts , so repeated inrush curent combined with a standing temperature.
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On Thursday, March 22, 2012 12:03:41 AM UTC-4, jeff_wisnia wrote:

Two fuses in series is pretty common. Always see this in microwave ovens and my wifes vacuum cleaner motor had two. Not sure if its belt and suspenders or just making it more likely to fail.
Jimmie
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"Jeff Liebermann"

** Horse manure.
One fuse is sufficient to break the circuit in case of current overload.

** Even worse horse manure.
Thermal fuses act on temperature, not current at all.
The max current rating given by makers is based on self heating to ensure the fuse stays within temp rating tolerance.
.... Phil
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wrote:

See: UL 60691 for testing of the the thermal fuse: <http://bbs.dianyuan.com/bbs/u/32/1122972217.pdf Section 10.8 discusses its use as a short circuit protection overcurrent fuse. (This is rev 3. Rev 5 is the current version).
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