These case materials are somewhat porous and through osmosis can cause contaminants to enter the capacitor. This can be aggravated by aqueous cleaning of circuit boards. Movement of the capacitor within the case can cause low I. Fatigue in the leads or mounting brackets can also cause a catastrophic failure.
The altitude at which hermetically sealed capacitors are to be operated will control the voltage rating of the capacitor. As the barometric pressure decreases so does the terminal "arc-over" susceptibility increase. Non-hermetic capacitors can be affected by internal stresses due to pressure changes. This can be in the form of capacitance changes or dielectric arc-overs as well as low I.
Heat transfer can be also affected by high altitude operation. Heat generated at the lead terminations cannot be dissipated properly and can result in high 12R losses and eventual failure. For space and nuclear applications, radiation capabilities of capacitors must be taken into consideration. Electrical degradation in the form of dielectric embrittlement can take place causing "shorts" or "opens" to occur.
Radiation effects in capacitors may be either transient or permanent. Transient effects are changes in the electrical parameters, which are changes in capacitance and decreases in insulation resistance only during irradiation. Special techniques and processes can be applied to capacitors to improve the radiation resistances for various plastic dielectrics.
Capacitors with inorganic dielectrics and cases, such as glass, are more radiation resistant than those utilizing organic materials such as oil-impregnated paper. In addition to electrical changes induced by ionizing radiation and particle bombardment, gas evolution from impregnants may build disruptive pressures in hermetically sealed cases.
Figures 2 and 3 are taken from Mil-HBK The failure rates are for general rates to be expected. Contact Online or Call Technical Bulletin No. Many of them simply die of old age. The most common electrolytic capacitors consist of three layers: a layer of metal foil, some kind of paper insulator, and a liquid electrolyte. When this happens, there are no visible signs from the outside. But when you test the capacitor out of circuit, you find it no longer behaves how it did when new. Once it drifts too far from its original properties, other components malfunction, since the capacitor is no longer doing the same work it used to do.
How long it takes varies. The caps in old tube radios, which usually date to the s or earlier, are almost always shot. The caps in ZX Spectrum computers are usually worn out and need replacing for the computer to work right. But the caps in the similarly-aged Commodore 64 are usually fine. Heat can accelerate this process. This could also account for the difference between the 64 and the Spectrum, as the Spectrum came in a smaller case, and its hot-running voltage regulator tended to cook the components inside, including the caps.
But sometimes capacitors fail because the electrolyte leaked out. Early surface mount capacitors, common in early 90s Amiga and Mac computers, very frequently leak, and when they do, they spew electrolyte all over the circuit board beneath them. The electrolyte is corrosive, so it can eventually eat through the coating on the motherboard and damage the traces underneath them.
It can also damage the pins on any chips it comes into contact with. In the early s, many PCs fell victim to leaky capacitors. This drove motherboard maker Abit out of business, and also severely hurt Dell. The problem in this case was botched industrial espionage. It can get to be over degrees on a hot summer day. But electrical overheating can be caused by the unit running too hard for too long. To help keep your HVAC from overheating, set the thermostat a little higher on those hot days.
Take other steps to improve your energy efficiency, like using reflective blinds on east- and west-facing windows. Power surges can cause a capacitor to fail, too. Those weaker surges can be caused by fluctuations in the electrical grid. It can effect even something as simple as large appliances in your home turning on and off. Protect your air conditioner and its capacitors from these power surges. Consider having an HVAC surge protector installed.
If the air conditioner continues to run with failing capacitors, it can cause much more serious and expensive issues down the road.
And how do failing capacitors affect your HVAC? This is one of many good reasons to have regular preventive maintenance. This includes checking the electrical components of your HVAC system.
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