Under different current conditions, failure modes include electrical puncture (see Figure 4), physical cracking (see Figure 5), and thermal runaway. Cracking happens because varistors are basically a ceramic material, and hitting them with a sharp high-amplitude surge is like hitting a dinner plate with a hammer.
Do varistors degrade over time?
MOVs degrade gradually when subjected to surge currents above their rated capacity. The end-of-life is commonly specified when the measured varistor voltage (Vn) has changed by + 10 percent.
How do I test a MOV varistor with a multimeter?
Turn the multimeter on and set its function knob to read resistance. Touch the meter probe tips to the MOVs leads and measure its resistance. If it has a resistance much under 100 ohms, it has blown. Desolder and remove the remaining lead and remove the MOV from the equipment.
Do surge protectors degrade over time?
Yes, a surge protector isnt designed to last forever and will eventually wear out.
Are varistors bidirectional?
Varistors are bidirectional components suitable for both AC and DC circuits. They come in different design packages.
Does Zener diode break down voltage?
A Zener diode is a silicon semiconductor device that permits current to flow in either a forward or reverse direction. The Zener diode has a well-defined reverse-breakdown voltage, at which it starts conducting current, and continues operating continuously in the reverse-bias mode without getting damaged.
How many years do surge protectors last?
Yep, thats right: Surge protectors dont last forever. Most estimates put the average lifespan of a surge protector at three to five years. And if your home is subject to frequent brownouts or blackouts, you might want to replace your surge protectors as often as every two years.
What happens when a surge protector goes bad?
Yes, a surge protector isnt designed to last forever and will eventually wear out. The bad news is that its almost impossible to tell when a surge protector wears out. Which means, you might think your appliances are protected against dangerous power surges when they really arent.
Is zener diode reverse biased?
Zener diodes are simply reverse-biased diodes that can withstand operating in breakdown. As the reverse bias voltage increases, Zener diodes continue to conduct a constant amount of current (the saturation current), until a certain voltage is reached.