Can a PTC fuse blow out and malfunction after it resets? The attached image shows a PTC that seems to have blown out. How do you determine if it needs to be replaced or not?
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(1) Sometimes you need to wait for a couple of days for a polyfuse to reset. (2) Some references: https://raspberrypi.stackexchange.com/questions/104596/rpi3b-micro-usb-connector-got-15v-power-is-it-dead-can-i-save-it/104614#104614. – tlfong01 May 21 '22 at 05:45
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1Looks bad soldered anyway, remove it and look at the pad, there may be a surprise waiting.. – Jens May 21 '22 at 06:01
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3With that soot around it, I certainly wouldn't trust it. It's unusual for a polyfuse to fail, but certainly possible; anything will fail if you use it wrong enough. – Hearth May 21 '22 at 06:16
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2What fault condition do you think may have caused this? – Bruce Abbott May 21 '22 at 09:35
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2They can "blow" and reset repeatedly, but they do have magic smoke in them. If it gets out they may not function correctly any more. The black marking on the board could be a sign that the magic smoke escaped. You could remove it and measure the resistance and compare it with the datasheet. – user57037 May 21 '22 at 09:53
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2I've seen plenty of PTCs burn, but not like that. The top side looks pristine. You can do some simple resistance measurements that should give an idea if the device has failed or not. Does the circuit still work? – Kartman May 21 '22 at 12:05
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1water entering into the cable shorted a component and this PTC that was on the board to which the component was connected to. There is low resistance but after replacing the component it works for a second and then stops. So I am wondering if the PTC has anything to do with this. – Boon May 21 '22 at 18:20
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I am aware of one way to make a polyfuse fail. Excess fault currents do this. If your total circuit resistance is low like 230VAC mains or say 48VDC telecom or say an 18 cell lead acid forklift battery and the polyfuse is too small it will fail permanently if there is a short circuit. Note that the DCR of these fuses is very low so you can destroy these devices at voltages of a fraction of their rating.
