Timeline for Why does water short out PCBs? (i.e. Why doesn't electricity follow the path of least resistance?)
Current License: CC BY-SA 4.0
17 events
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| May 26 at 14:06 | comment | added | Russell McMahon♦ | @xenia If water is genuinely pure electrolysis would occur extremely slowly by normal timespans. I saw a figure of 18 megohm/cm - which is not going to make anything happen anytime soon. That's at the equilibrium 10^-7 = pH of 7 hydrogen ion concentration. But equally, extremely small amounts of contaminants will move the pH substantially. Practice shows that electrolysis happens in common practice - dropping a cellphone or camera in fresh water MAY be survivable. In a toilet or the sea gives lots of nice ions and is often fatal. (My daughter's iPhone & a camera of mine suffered as described.) | |
| May 25 at 11:33 | comment | added | xenia | @RussellMcMahon I do not doubt that electrolysis will happen in the water and that it will lower the resistance of the water a lot. However, I find it very hard to believe that the resistance of the water will be comparable to that of the very conductive copper, which is usually only a few milliohms. If you could provide some source or calculation even in the most extreme case showing the approximate resistance of the water I would be grateful. | |
| May 9 at 5:13 | comment | added | Russell McMahon♦ | @Winny. Yes. "Pure" water has a pH of 7 which directly relates to its "self ionisation" (as I know you know). | |
| May 8 at 11:57 | comment | added | Russell McMahon♦ | @Vorac I did a bad job of answering your query 11 years ago.. Almost as bad - I'll refer you to Wikipedia :-). Electrolysis in liquid and air breakdown are extremely different - fortunately. || They note: Water electrolysis starts at 1.23V. | As of 2022, commercial electrolysis requires around 53 kWh of electricity to produce one kg of hydrogen, which holds 39.4 kWh (HHV) of energy wiki2.org/en/Electrolysis_of_water | |
| May 8 at 11:53 | comment | added | winny | On top of "water is completely pure some ionisation will occur", the more pure it is, the more aggressive it will be on surrounding materials to steal ions from them. Water really wants to be in balance and somewhat conductive. | |
| May 8 at 11:46 | history | edited | Russell McMahon♦ | CC BY-SA 4.0 |
added 2070 characters in body
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| May 8 at 6:38 | comment | added | Russell McMahon♦ | @xenia The answer down to just above "Plus:" clearly sets out what happens in reality. Ohm's law predicts that an extremely small current will flow through only slightly impure water. THEN the fun begins as covered following "Plus:" - even an extremely small amount of contamination results in ionisation products which increase conductivity which further increases ionisation products which ... . What started out as a small portion of the total current can quite rapidly turn into a major current path. | |
| May 8 at 6:32 | comment | added | Russell McMahon♦ | A downvote 11 years on. It seems likely that somebody does not understand the subject very well at all. If so, I suggest that you read my answer more carefully. | |
| May 4 at 20:15 | comment | added | xenia | -1: In all but the most extreme circumstances, the water will have a resistance many orders of magnitude larger than the copper. While of course some current will still flow through the water, the water's resistance is so much higher than that of the copper that "electricity follows the path of least resistance" will be very close to reality. This answer completely misses the point that different exposed pads on the circuit board might not be connected directly with a low-resistance copper path, and then the resistance of the water will be low enough to conduct a significant amount of current. | |
| Apr 4, 2013 at 10:29 | comment | added | Russell McMahon♦ | @Vorac - note that you only need to START small. Get conduction going and stuff happens and the ionisation grows. | |
| Apr 4, 2013 at 10:28 | comment | added | Russell McMahon♦ | @Vorac Starting with "It happens" + deionised water doesn't conduct the most common reason is liable to be even small trace contaminants initially plus impurity of the contaminating water. I have seen and heard of various things destroyed by liquids plus battery action and, as mentioned above, I have two amazing examples of how prompt action can stop major damage when massively conductive contamination is present (seawater and pool chlorine). I had a friend who had a camera in a "waterproof" plastic container destroyed by row-boat bilge water in the time it took to row out to a moored yacht. | |
| Apr 4, 2013 at 7:09 | comment | added | Vorac | Great answer, Russell! Question: how come the low 4.2VDC of portable devices manage to ionize water and pass such a huge current (miliamps) in order to burn out electronics? Could you please provide a sample simple calculation? For example, I believe one needs 10kV to ionize 1 cm of air gap! | |
| Jan 30, 2013 at 2:31 | comment | added | Chef Flambe | Pagers: volunteer fire halls are still HUGE users...some ambulance services...support staff in hospitals, food servers and also given to people waiting for tables at restaurants so they can wonder away until the table is ready. It's a tech on it's last breathe but going down fighting. | |
| Jan 24, 2013 at 5:43 | comment | added | DrFriedParts | +1 For explaining this mysterious "Pager" reference. Thank you. | |
| Jan 24, 2013 at 3:19 | comment | added | Asker | Beautifully answered. This was easy to understand. Thank you. | |
| Jan 24, 2013 at 3:15 | vote | accept | Asker | ||
| Jan 24, 2013 at 0:46 | history | answered | Russell McMahon♦ | CC BY-SA 3.0 |