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Electrolytic Capacitor - wrong polarity Marking for the negative Pol outsidee
Electrolytic Capacitor - wrong polarity Marking for the negative Pol outsidee
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Old 12th October 2017, 11:08 AM   #1
tiefbassuebertr is offline tiefbassuebertr  Germany
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Location: D-55629 Schwarzerden
Default Electrolytic Capacitor - wrong polarity Marking for the negative Pol outside

Short time after switch on a diy power supply one of the capacitors from Nippon Chemicon's LXZ-Series - go to
RAD LXZ 35 - 2K7: ELKO, 2700 F, 35 V, 105 C bei reichelt elektronik
runs very hot.
The reason therefore was the operating in the reverse mode.
This was happen, because the shrinking tube of that capacitor was wrongly attached, whereby the marking for the negative pole was at the longer wire for the positive pole.
This means in the future for me, that the marking of electrolytic capacitors must always be doubtful.

Therefore I want an easy measurement methody for checking the really right polarity.
Thanks for advices.

Last edited by tiefbassuebertr; 12th October 2017 at 11:23 AM.
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Old 12th October 2017, 11:37 AM   #2
DF96 is offline DF96  England
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Apply a little current. Monitor the voltage. If it rises smoothly past a few volts then the polarity is correct. If it gets stuck at a low voltage then polarity is wrong, so reverse it and try again but then be aware that you may need to re-form the cap as the test may have slightly damaged the oxide layer.
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Old 15th October 2017, 02:54 PM   #3
tiefbassuebertr is offline tiefbassuebertr  Germany
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Thanks for your advices.
Under
surface mount - Polarity of unmarked smt electrolytic capacitor - Electrical Engineering Stack Exchange
there is to read this:

If they really are unmarked polarised (extremely unlikely) then a possibly destructive method of testing for polarity is to gradually apply a current limited voltage (e.g slowly up to ~25% of rated voltage, limited to ~10mA) in both directions across the cap whilst measuring current - if polarised and the wrong way round you should start to see a steadily rising current flow. Can be done with a bench power supply, and put a shield of some sort over the cap just in case it decides to detonate ;-)

I tested with the bench supply, above ~7V across reverse polarity with a 100uF/35V aluminium electrolytic, the leakage current rises above 1mA (measured using bench display) and quickly starts to accelerate upwards.
I also just tested this with a multimeter in series with the bench supply (more sensitive than the bench supply measure) measuring current across the same capacitor:

Using 5V with correct polarity produced ~1uA leakage.
With 5V and reverse polarity the leakage started at around 25uA and gradually got higher, after around 30 seconds it was at 50uA.
Even at 3V it was reasonably obvious which way round it was - the reverse leakage was at least twice that of the correct polarity.


additional URLs:
http://slot-tech.com/interesting_stu...20-%204003.pdf
https://web.archive.org/web/20060509.../pdf/TT139.pdf
Slowing 209.59.178.49&c=1&t=43023.2879409722
Determine the polarity of aluminium electrolytic capacitor - Electrical Engineering Stack Exchange
https://nepp.nasa.gov/docuploads/E12...s_Behavior.pdf
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