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Well, until today I didn't even know capacitor can have orientation! So more productive Wednesday than yours. In entry level electronics class I had decades ago

Well, until today I didn't even know capacitor can have orientation! So more productive Wednesday than yours. In entry level electronics class I had decades ago it was always treated as a component that works the same way no matter in which direction the current flows.

fredoralive 2y ago
There are polarised and unpolarised capacitors. Stuff like basic decoupling capacitors tend to be unpolarised.
Filligree 2y ago
Ceramic capacitors don't have polarity. Electrolytic ones do. Thing is, electrolytic capacitors have far higher capacitance for their size -- though also higher resistance. It's something to check, but the polar ones should be clearly marked as such.
- magic_smoke_ee 2y ago
  Electrolytic capacitors are kinda like lead-acid batteries in that they are polarized through manufacturing processes. A voltage is applied in the factory to anodize the anode with a thin oxide layer. For fun, I think it would be possible to buy a quality low voltage cap and reverse the polarity of it in-situ which would remove the anodization from the new cathode and deposit a new layer on the new anode (former cathode) hopefully without over-pressurizing it to bursting, albeit with much less anticipated lifespan. PSA: Electrolytic capacitors have a rough lifespan of 10 years. Any much older than that need to be checked out-of-circuit for ESR and then capacitance. Also, tantalums (historically) suck(ed). [0] Quality audio equipment from the 80's like a/d/s/ car amps used only ceramic caps and other over-engineered passives, and have the potential (pun intended) to basically last forever. 0. https://www.eevblog.com/forum/projects/whenwhy-(not)-to-use-tantalum-capacitors-pros-cons-alternatives/msg359601/#msg359601 https://www.eevblog.com/forum/projects/whenwhy-(not)-to-use-...
  - kevindamm 2y ago
    Or much shorter, around two years, if it was part of the Capacitor Plague. https://en.wikipedia.org/wiki/Capacitor_plague#Premature_failure https://en.wikipedia.org/wiki/Capacitor_plague#Premature_fai... The normal lifespan of a non-solid electrolytic capacitor of consumer quality, typically rated at 2000 h/85 °C and operating at 40 °C, is roughly 6 years. It can be more than 10 years for a 1000 h/105 °C capacitor operating at 40 °C. Electrolytic capacitors that operate at a lower temperature can have a considerably longer lifespan. ... The life of an electrolytic capacitor with defective electrolyte can be as little as two years.
    - Workaccount2 2y ago
      This is also why so many LED bulbs are shit, lots of heat in a small space full of electrolytic caps.
      - magic_smoke_ee 2y ago
        Intentional planned consumption/obsolescence by design. This class of problem is where under-regulation and lack of standards benefits only sellers and cheats buyers. PS: Also, Amazon should be required to test all of the electronic, safety, and food products on its site such that they can prove safety and standards conformance.
        Filligree 2y ago
        That, and customers insisting on preexisting form factors. Fitting the electronics and LEDs into the space of a traditional lightbulb comes with compromises, such as not having proper heat dissipation on either.
        BlueTemplar 2y ago
        Yeah, you would think they would be two separate devices by now...
        2y ago
- canadianfella 2y ago
  [dead]
- 83 2y ago
  Bipolar electrolytic capacitors are a thing, I recently had to solder up a handful of them in some audio circuits.
nuancebydefault 2y ago
Once you have experienced blowing up a reversed elcap you will never forget its orientation. I never understood though what makes it leak current and hence heat up.
- kevindamm 2y ago
  There's an aluminum oxide layer as a coating on both the anode and cathode inside the (electrolytic) capacitor. Under forward voltage it will gradually thicken but under reverse voltage it dissolves and causes a short. This increases the temperature which causes hydrogen ions to separate and bubble through the material, increasing pressure within the capacitor package until it bursts.
  - consp 2y ago
    The thickening under forward voltage explains the "recovering cap" phenomenon with some old caps. Didn't know that.
- marcosdumay 2y ago
  Modern electrolytic caps don't burn like they used to. The last few times I made a mistake, there wasn't even an explosion, even less a short-circuit. The thing slowly boiled and bubbled or unfolded. Anyway, it blows up because the capacitor's insulation layer isn't some stable material, it's a tiny oxide layer built over the metal plate by anodization. If you put a high voltage on it with the wrong polarity, you reverse that anodization and short the liquid and the metal electrodes.

fredoralive 2y ago

There are polarised and unpolarised capacitors. Stuff like basic decoupling capacitors tend to be unpolarised.

Filligree 2y ago

Ceramic capacitors don't have polarity. Electrolytic ones do. Thing is, electrolytic capacitors have far higher capacitance for their size -- though also higher resistance. It's something to check, but the polar ones should be clearly marked as such.

magic_smoke_ee 2y ago
Electrolytic capacitors are kinda like lead-acid batteries in that they are polarized through manufacturing processes. A voltage is applied in the factory to anodize the anode with a thin oxide layer. For fun, I think it would be possible to buy a quality low voltage cap and reverse the polarity of it in-situ which would remove the anodization from the new cathode and deposit a new layer on the new anode (former cathode) hopefully without over-pressurizing it to bursting, albeit with much less anticipated lifespan. PSA: Electrolytic capacitors have a rough lifespan of 10 years. Any much older than that need to be checked out-of-circuit for ESR and then capacitance. Also, tantalums (historically) suck(ed). [0] Quality audio equipment from the 80's like a/d/s/ car amps used only ceramic caps and other over-engineered passives, and have the potential (pun intended) to basically last forever. 0. https://www.eevblog.com/forum/projects/whenwhy-(not)-to-use-tantalum-capacitors-pros-cons-alternatives/msg359601/#msg359601 https://www.eevblog.com/forum/projects/whenwhy-(not)-to-use-...
- kevindamm 2y ago
  Or much shorter, around two years, if it was part of the Capacitor Plague. https://en.wikipedia.org/wiki/Capacitor_plague#Premature_failure https://en.wikipedia.org/wiki/Capacitor_plague#Premature_fai... The normal lifespan of a non-solid electrolytic capacitor of consumer quality, typically rated at 2000 h/85 °C and operating at 40 °C, is roughly 6 years. It can be more than 10 years for a 1000 h/105 °C capacitor operating at 40 °C. Electrolytic capacitors that operate at a lower temperature can have a considerably longer lifespan. ... The life of an electrolytic capacitor with defective electrolyte can be as little as two years.
  - Workaccount2 2y ago
    This is also why so many LED bulbs are shit, lots of heat in a small space full of electrolytic caps.
    - magic_smoke_ee 2y ago
      Intentional planned consumption/obsolescence by design. This class of problem is where under-regulation and lack of standards benefits only sellers and cheats buyers. PS: Also, Amazon should be required to test all of the electronic, safety, and food products on its site such that they can prove safety and standards conformance.
      - Filligree 2y ago
        That, and customers insisting on preexisting form factors. Fitting the electronics and LEDs into the space of a traditional lightbulb comes with compromises, such as not having proper heat dissipation on either.
        BlueTemplar 2y ago
        Yeah, you would think they would be two separate devices by now...
      - 2y ago
canadianfella 2y ago
[dead]
83 2y ago
Bipolar electrolytic capacitors are a thing, I recently had to solder up a handful of them in some audio circuits.

nuancebydefault 2y ago

Once you have experienced blowing up a reversed elcap you will never forget its orientation. I never understood though what makes it leak current and hence heat up.

kevindamm 2y ago
There's an aluminum oxide layer as a coating on both the anode and cathode inside the (electrolytic) capacitor. Under forward voltage it will gradually thicken but under reverse voltage it dissolves and causes a short. This increases the temperature which causes hydrogen ions to separate and bubble through the material, increasing pressure within the capacitor package until it bursts.
- consp 2y ago
  The thickening under forward voltage explains the "recovering cap" phenomenon with some old caps. Didn't know that.
marcosdumay 2y ago
Modern electrolytic caps don't burn like they used to. The last few times I made a mistake, there wasn't even an explosion, even less a short-circuit. The thing slowly boiled and bubbled or unfolded. Anyway, it blows up because the capacitor's insulation layer isn't some stable material, it's a tiny oxide layer built over the metal plate by anodization. If you put a high voltage on it with the wrong polarity, you reverse that anodization and short the liquid and the metal electrodes.