What happens if the voltage is too high or too low?

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named volt.: 166 In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The old SI definition for volt used power and current; starting in 1990, the quantum Hall and Josephson effect were used, and recently (2019) fundamental physical constants have been introduced for the definition of all SI units and derived units.: 177f, 197f Voltage or electric potential difference is denoted symbolically by {\displaystyle \Delta V}\Delta V, simplified V,or U,for instance in the context of Ohm's or Kirchhoff's circuit laws.

Voltage that is too high can cause premature failure of electrical and electronic components (e.g. circuit boards) due to overheating. The damage caused by overheating is cumulative and irreversible. Frequent episodes of mild overheating can result in the same amount of component damage as a few episodes of severe overheating. Like slicing a loaf of bread – you can have many thin slices or a few really thick slices – but when you get to the end, you’re done.

Motors can, on the other hand, often benefit from voltages that tend to be a little bit high. The reason is fairly simple. As the voltage level goes up, the current is reduced and lower current usually equates to less heat generation within the motor windings. There is a point where the voltage level supplied can be so high as to damage a motor but this level is far higher than that for electronics.

Keeping electrical and electronic components cool tends to insure their longevity. Slight reductions in voltage levels may permit many electronics to perform perfectly well while minimizing their temperature. Of course, the same is not true of motors.

Just as higher voltages can help reduce motor operating temperatures, low voltage is a major cause of motor overheating and premature failure. A low voltage forces a motor to draw extra current to deliver the power expected of it thus overheating the motor windings. The rule of thumb for motors is “for every 10 degrees C (50 degrees F) a motor is operated above its rated temperature, motor life will be decreased by 50%”.

More than motors and circuit boards are at risk for damage when voltage levels are bad, but chronic problems with either is often an indication of a voltage problem.

https://en.wikipedia.org/wiki/Voltage