Author Topic: Unobtanium fuse  (Read 371 times)

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Offline dunkemhigh

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Unobtanium fuse
« on: April 26, 2021, 01:09:10 pm »
I have a CCTV installation tester and one function is the ability to power the camera under test from the device. The output is specified as 12V 1A and in the dim past (this is many years old) I recall it powering cameras without issue. Then some while back it kind of didn't, in that sometimes it would work but other time the camera would repeatedly reset. It's not a feature I use that often, but it annoyed me enough yesterday that I resolved to fix it...

So, in essence, there is a resettable fuse between the supply and output, as captured in the photo. If I put a load of 180mA or so on there, the output voltage drops to 10V, and then if I wind it up to a bit over 200mA the fuse trips. My cameras typically sink 180mA on power-up (winding the auto-focus in then out) and settle at about 80mA after that.

Obviously the fuse is not up to spec, so I go looking for a replacement. However, it is 0805-sized and I can't find anything in that size with 12V 1A rating (or even close). Sure, I can go for 750mA but at 6V, or I can go for 15V but at 100mA. It's the classic two out of three thing.

Am I missing something about the fuse spec, or have they pulled a fast one and ignored some aspect on the installed fuse?
 

Offline wraper

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Re: Unobtanium fuse
« Reply #1 on: April 26, 2021, 01:30:08 pm »
However, it is 0805-sized
Except it's 1206.
 

Offline wraper

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Re: Unobtanium fuse
« Reply #2 on: April 26, 2021, 01:43:23 pm »
Should be Polytronics (PTTC) SMD1206P075TF/13.2 https://datasheet.lcsc.com/lcsc/2003112036_PTTC-Polytronics-Tech-SMD1206P150TFT_C495353.pdf
0.75A hold current, 1.5A trip current, 13.2V VDC.
« Last Edit: April 26, 2021, 02:22:04 pm by wraper »
 
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Offline dunkemhigh

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Re: Unobtanium fuse
« Reply #3 on: April 26, 2021, 01:55:06 pm »
Quote
Except it's 1206.

That would explain a lot! Remeasuring, you are correct - I must've had a brainfart with the calipers.

Quote
Should be Polytronics (PPTC) SMD1206P075TF/13.2

Thanks very much  :-+
 


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