Electronics > Beginners
DIY PSU part 2
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janoc:

--- Quote from: Pirateguy on October 17, 2018, 11:19:58 am ---so, if the fuses only protect the psu, there is no real point in having more then 1, is there?

--- End quote ---

The problem with a polyfuse (or even a normal fuse) is that it is too slow to protect semiconductors from overcurrent. Furthermore, when bringing up a new circuit you want to set the current limit as low as possible to limit the current that can flow through the circuit in case there is some mistake. Only when you are reasonably sure that everything is working as intended you start raising that limit. E.g. I am commonly using 10-20mA current limit when bringing up a new circuit - that's so low that even if I goof it won't destroy most components.

If your only current limiting device is a polyfuse then that limits your current choices a lot. Your polyfuses are much bigger than 20mA, I believe. That's why I wrote that a polyfuse is a good thing to protect against a fire (I assume you want to use an ATX supply to power this contraption - those can deliver 20A like nothing, which will set things on fire if there is a problem) and destroying the power supply (even though they do have short circuit and overload protections). However, it will not do so much for your device under test - even the smallest polyfuse you put there will likely allow enough current to fry your circuit if there is a problem.
PointyOintment:

--- Quote from: Pirateguy on October 16, 2018, 10:47:55 pm ---
--- Quote ---The internal thermometer doesn't get disconnected when you use the external one? That seems like it would prevent accurate reading of the external thermometer except when the two happen to be at the same temperature.
--- End quote ---

well technically there is no external thermometer, just the probe would be external.
i have one of those PC sensors and a stick one that came with a multimeter that has a thermometer in it.
the thermometer is inside the display module, that's why i am worried it will be influenced by the ambient temp in the box,
even when the internal sensor is disconnected.

--- End quote ---
Oh—you're worried about the temperature of the cold junction. Does your thermometer module lack cold junction compensation?
Pirateguy:

--- Quote from: PointyOintment on October 17, 2018, 09:12:30 pm ---Oh—you're worried about the temperature of the cold junction. Does your thermometer module lack cold junction compensation?

--- End quote ---

well it's the cheapest one i could find on ebay, i don't expect any luxuries lol.
https://www.ebay.com/itm/New-Digital-LCD-Thermometer-Temperature-Meter-Gauge-Molex-Panel-Mount-C-F-PC-MOD/122513357209?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
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