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Capacitor safety vent audible sound

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ogden:

--- Quote from: Siwastaja on February 07, 2021, 01:39:03 pm ---Yes, I think if capacitor "state-of-health" measurement is needed, then ESR monitoring is the simplest, most reliable, and most useful way to do it because being a motor drive, the known current ramp already exists, only thing left is measure voltage ramp.

--- End quote ---
This is other way to say "measure ripple voltage", at given load/current. Power bus ripple peak detector does not sound like bad idea for hi-end devices, nor it would be complicated circuit. One needs AC decoupling, rectifier diode, lowpass RC filter and comparator or ADC and means of reporting problem.

Idea for OP: you can detect bulging/ruptured capacitor by gluing thin/brittle wire over it's rupture area and check continuity.

wraper:

--- Quote from: ogden on February 07, 2021, 07:22:54 pm ---This is other way to say "measure ripple voltage", at given load/current. Power bus ripple peak detector does not sound like bad idea for hi-end devices, nor it would be complicated circuit. One needs AC decoupling, rectifier diode, lowpass RC filter and comparator or ADC and means of reporting problem.

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But you likely to have several power buses and capacitors in places hard to measure, say in primary side of SMPS. In many places dead capacitor won't increase any ripple to measure at all. Say would you bother to measure ripple on Vcc/Vin of PWM controller IC on primary side of PSU? Yet capacitor sitting there is among parts which fail the most often.

Ian.M:
Use a crappy small electrolytic there in a Muntzed PSU design, put it right next to the chopper heatsink, and it will certainly be a leading cause of failure.  Small can electrolytics are notorious for not tolerating high temperatures and ripple currents well due to their small surface area for heat dissipation and once they start to degrade, due to their extremely low reserve of electrolyte in their tiny volume, rapidly fail totally.   Use an appropriately rated well chosen solid dielectric capacitor and you can virtually eliminate failures due to excessive ripple at the primary side SMPS controller power pin.

ogden:

--- Quote from: wraper on February 07, 2021, 07:40:30 pm ---But you likely to have several power buses and capacitors in places hard to measure, say in primary side of SMPS. In many places dead capacitor won't increase any ripple to measure at all. Say would you bother to measure ripple on Vcc/Vin of PWM controller IC on primary side of PSU? Yet capacitor sitting there is among parts which fail the most often.

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You always can find circumstances where implementing safety device fault detector is impractical. If somebody have illusion that capacitor failure detector shall be built-into every device where electrolytic capacitors are present then he is mistaken indeed :) Yes I agree with you that proper design and proper choice of components shall be paramount. If  those two are not enough only then next level of safety reliability measures shall be engineered.

Siwastaja:

--- Quote from: ogden on February 07, 2021, 07:22:54 pm ---This is other way to say "measure ripple voltage", at given load/current. Power bus ripple peak detector does not sound like bad idea for hi-end devices, nor it would be complicated circuit. One needs AC decoupling, rectifier diode, lowpass RC filter and comparator or ADC and means of reporting problem.

--- End quote ---

Actually any properly designed motor drive already measures the DC link voltage for various reasons: control algorithm feedforward, to stop regenerating and let the motor freewheel if DC link voltage rises above maximum...

So really the only thing to do is to make sure the existing measurement circuit has enough bandwidth - maybe by reducing the amount of RC filtration, and increasing sample rate in software. If you sample twice per output stage PWM cycle, you have enough data already to calculate ESR on the fly: you know all dV, dI and dt.

This may be zero hardware cost and not very complex on the software side, too. The biggest hurdle is to decide how to report and handle the error. And, avoiding false positives. For example, cold capacitors have higher ESR, but this isn't a serious problem because the capacitors will self-heat so the ESR lowers back to normal range.

wraper has a point though, even if you monitor the trivial motor controller DC link, the big picture will have dozens of power supplies with dozens of DC links that are not trivial to monitor. By Murphy's law, everything else fails except your fancy monitored motor drive DC link. This is unsurprising: often the small elcap in an auxiliary supply fails first, maybe because the designer didn't think that supply is critical.

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