Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 13, 2021 15:48:30 GMT -5
The thermal rating of a capacitor is determined BY the materials it is made from and has no impact on the voltage or capacitance rating. The thermal rating impacts lifespan depending on the actual temperature the unit is exposed TO, but the capacitance values are not affected. There is no such thing as "thermal rating of capacitance," it is simply a steady-state exposure rating for the component materials, with lifespan increasing the farther away from the limit you operate. Perhaps I had not phrased my question correctly, however, found the answer here under capacitor working temperatures: www.electronics-notes.com/articles/electronic_components/capacitors/specifications-parameters.php"Working temperature: All capacitors have a limited working temperature range whether ceramic capacitors, electrolytic capacitors, tantalum capacitors or whatever type. This specification details the limits within which the capacitor will work satisfactorily and over which it is designed to operate. Some aspects that limit the working range of a capacitor are the voltage - this falls with increasing temperature; the ripple current - again lower with increasing temperature. The lower temperature specification can be governed by a number of factors. One is the electrolyte operation in components such as electrolytic capacitors. The working temperature is particularly important for electrolytic capacitors as their expected life falls rapidly with increasing temperature. Temperature coefficient: Capacitors, like all components vary with temperature. The degree is relatively small, and does not make a difference in circuits where the value is not critical, but in others where the circuit is dependent upon the exact value, e.g. an LC oscillator, etc, the temperature coefficient can be very important. The temperature coefficient is often expressed as the variation in parts per million per degree Celsius." |
|
DYohn
Emo VIPs 
Posts: 18,485
|
Post by DYohn on Apr 13, 2021 16:19:35 GMT -5
All of that is moot to the discussion at hand. The design - including the capcitor choice - is sufficient for the operating conditions. The cap that failed simply failed. This happens.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 13, 2021 16:26:27 GMT -5
All of that is moot to the discussion at hand. The design - including the capcitor choice - is sufficient for the operating conditions. The cap that failed simply failed. This happens. Temperature was brought up and I merely inquired on whether varying temperatures affect a capacitor. I had no idea about the temperature value on the actual capacitor but I was inquiring on whether operating temperatures affect capacitors. And, I don't think it is moot considering nobody even asked about whether the guy w/ failed capacitors in equipment lives in Death Valley and has it encased in an oven at 400 degrees  But I get your point and yield back while thanking you for your input! |
|
|
|
Post by bobbyt on Apr 13, 2021 19:31:09 GMT -5
All of that is moot to the discussion at hand. The design - including the capcitor choice - is sufficient for the operating conditions. The cap that failed simply failed. This happens. Temperature was brought up and I merely inquired on whether varying temperatures affect a capacitor. I had no idea about the temperature value on the actual capacitor but I was inquiring on whether operating temperatures affect capacitors. And, I don't think it is moot considering nobody even asked about whether the guy w/ failed capacitors in equipment lives in Death Valley and has it encased in an oven at 400 degrees But I get your point and yield back while thanking you for your input! The amps in question are enclosed in the Airmotiv speakers, on stands in a climate controlled room, which happens to be smaller and surrounded by more neighbors than my prior place, so they're run at a fraction of their potential. So my assumption here is that a higher-rated cap would just mean that the 30 or 40 or whatever temp they hit would be even further below what they're designed to handle, so maybe I'd get 15 years out of them instead of 9-10... As a quick update, I fought my way through the elastic/tar stuff Emotiva secured them with while unsoldering, and the "good" cap showed +45mV (ie .045v) while the stained one showed -35mV (ie -.035v), assuming the big dash on the side is the negative. I don't know if there's a drain resistor at power-off so I chalked this up to both being at 0v, and put a 9v alkaline battery across the terminals. Battery measured 7.89v, and after 30 seconds I measured 7.86v on the "good" cap and about -0.030 on the stained one, so it seems like I've found the culprit. |
|
|
|
Post by bobbyt on Apr 13, 2021 19:49:51 GMT -5
You also need to distinguish where the heat is coming from. If the tweeter itself is becoming warm that would suggest DC current leaking through it and heating the printed voice coil. This in turn would suggest a DC offset on the output of the internal tweeter amplifier. This is the sort of situation that is bad, and will tend to get worse, resulting in a fried tweeter. It's also unlikely to be caused by a bad power supply capacitor alone - although not impossible. However, the tweeter is a thin part, with a shell and insides made up of plastic and metal. It's possible that the heat is coming from the electronics inside... And is simply warming up the tweeter from behind.
(The tweeter will conduct heat and will also feel warmer to the touch than the surrounding wood cabinet.)
I was aware DC will overheat the voice coil but not certain whether a continuous AC signal could mask DC, or if the failed cap could be acting like a resistor, etc. I noticed the heat because I put my hand across the tweeter grille, basically contact distance, and it wasn't enough to heat the cabinet. But I didn't try powering it up with the back plate open to hunt down the source, so here's hoping it's resolved with the cap swap... |
|
|
|
Post by 405x5 on Apr 14, 2021 14:10:48 GMT -5
I would have the speaker professionally serviced. If other components are damaged as a consequence of the capacitor failure you will be back to square one.
|
|
|
|
Post by bobbyt on Apr 14, 2021 21:28:41 GMT -5
I would have the speaker professionally serviced. If other components are damaged as a consequence of the capacitor failure you will be back to square one. I'm afraid that was never an option. I'm armed with a soldering iron, a multimeter, and a Mouser account. If I don't return with an update, assume I have discovered the current limits of the new caps or fired a tweeter into the ceiling. |
|
|
|
Post by 405x5 on Apr 14, 2021 21:55:12 GMT -5
I would have the speaker professionally serviced. If other components are damaged as a consequence of the capacitor failure you will be back to square one. I'm afraid that was never an option. I'm armed with a soldering iron, a multimeter, and a Mouser account. If I don't return with an update, assume I have discovered the current limits of the new caps or fired a tweeter into the ceiling. |
|
