I not too long ago got here throughout a disturbing piece of reports a few recall of Ryobi pressurized washers on FOX Enterprise (Determine 1). I received some footage from there and elsewhere, which, with a little bit rearrangement and supplementation, level out a really actual hazard.
Determine 1 Screenshot of the information article on the stress washer recall. Supply: Fox Enterprise
The so-called overheating capacitors can apparently be recognized as proven in Determine 2.
Determine 2 The overheating motor beginning capacitor beneath query. Supply: Amazon.com
This element supplies 300 µF, which is a magnitude of capacitance that may solely be obtained in aluminum electrolytic capacitors. Such capacitors can’t be allowed to expertise reverse voltage, although, so to attain the 250 VAC functionality, a pair of capacitors have to be utilized in sequence as proven in Determine 3.
Determine 3 Seize of a schematic that mixes two aluminum-electrolytic capacitors.
Every capacitor is paired with a diode that limits the reverse polarity that may seem throughout every capacitor to 1 ahead diode voltage drop, name that 0.7 V. Supposedly, that voltage restrict remains to be secure as reverse voltage throughout an aluminum electrolytic capacitor.
Nonetheless!!!! If one diode fails as an open circuit, the reverse voltage that may be imposed on its related capacitor can rise method above the diode restrict, and that capacitor can fail.
Determine 4 A SPICE instance of reverse voltage when one diode fails as an open circuit. Supply: John Dunn
Such a failure can result in a capacitor explosion.
Once I was in faculty, I had a lab associate with whom I might carry out every class experiment. One experiment concerned a 22-µF 16-V electrolytic capacitor. It was a tiny little factor.
Sadly, my associate (It was NOT me!) put that capacitor within the circuit board backwards, and it was pushed into reverse bias. It sat there for some time as the 2 of us had been discussing the circuit beneath check when abruptly that capacitor exploded!!
That explosion was LOUD!! Everyone inside fifty toes was wanting in our course. The aluminum shell of the capacitor had been torn open like a Tootsie Roll wrapper.
I believe that the Ryobi capacitor challenge was not from “overheating” as Determine 5 suggests, however that one of many diodes throughout the CD60 capacitor failed as an open circuit, which allowed extreme reverse bias to seem throughout its related capacitor. (If a diode had failed as a brief circuit, I doubt if the motor would begin.)
Determine 5 An unwise reassurance that the capacitor might not blow when put in backwards. Supply: LeftyMaker, YouTube
One would suppose that the CD60 capacitor would have a stress launch plug that might vent if inner stress received too excessive. If there’s such a mechanism, evidently generally it’s not working correctly. The sheer bodily measurement of the CD60 capacitor within the Ryobi product versus that little itty-bitty capacitor in my lab class makes me consider the CD60 capacitor as a possible hand grenade.
John Dunn is an electronics guide and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York College (MSEE).
Associated Content material
- Would higher electrolytic capacitors cut back e-waste?
- Capacitors–the previous decoupling standbys
- Guarantee lengthy lifetimes from electrolytic capacitors: A case examine in LED gentle bulbs
- Figuring out end-of-life, ESR, and lifelong calculations for electrolytic capacitors at greater temperatures
- Energy Ideas #50: Keep away from these widespread aluminum electrolytic capacitor pitfalls
The publish Stress washer recall and aluminum electrolytic capacitors appeared first on EDN.
