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| Measuring ESR of 100v capacitors |
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| Mp3:
Hi everyone :scared: I have two 22k uF 100v capacitors i want to test the ESR on. I have a Dick Smith design ESR meter but i dont want to fry it with 100v. How can i safely test it? PS can i do any useful tests with my fluke 101 on it? I thought testing DC voltage but my meter only reads something like 5k uF maximum. |
| Ian.M:
Discharge the capacitors before testing. |O |
| Mp3:
--- Quote from: Ian.M on August 18, 2018, 11:16:30 am ---Discharge the capacitors before testing. |O --- End quote --- Isn't it potentially dangerous to short out a 100v capacitor?? |
| ArthurDent:
Ian.M said discharge, not short. It is common to use an appropriate value resistors to drain the charge from a capacitor without putting a direct short across it. You could even use an incandescent 120 volt light bulb for a 100 volt capacitor. Keep in mind that if you don't leave the load across the capacitor for a long enough time, dielectric absorbtion can cause some voltage to redevelop. High voltage low leakage capacitors are stored with wires across the terminals for safety. |
| Ian.M:
Yes. If you short a large capacitor the high transient current can even vaporise what you shorted it with or its terminals or internal connections. However, as Arthur just pointed out, discharging a capacitor can be done without shorting it - just use a suitable wirewound resistor that can handle the peak power. As a rule of thumb, the peak wattage (from V2/R) shouldn't exceed 10x the resistor's continuous rating. A 22uF 100V cap only stores 0.11 Joules of energy when fully charged. Discharging it by shorting it directly across its pins ONCE is unlikely to damage it. Repeated shorts when fully charged, or shorting a larger or higher voltage cap with more stored energy would not be advisable. |
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