What are the effects of power dips (brownouts) on computers?

Question

A lot of UPSs advertise they protect against "brownouts". What exactly is the effect on a computer if the voltage goes low but not completely out? Where I'm currently living the lights frequently flicker and dim and my UPS kicks in.

Answer 1

Your computer can be affected by brownouts at two levels, above and below the power supply's minimum operating voltage.

Above the minimum

Utility companies routinely cope with excessive power demands by using controlled brownouts, temporarily dropping the voltage 5-10% (it can be higher; if your UPS kicks in, it's higher). Your power supply is designed to operate at voltages commonly seen during controlled brownouts (this is the "under-voltage protection" they mention in the product specs). However, their components run hotter at reduced input voltage.

If you're in an area with frequent, deep, and prolonged brownouts, this could theoretically shorten the service life of the power supply (but no other components should be affected). There's really no way to quantify this because of the great variability in conditions, power supply designs, etc. A UPS will kick in at a reduced line voltage that is still above the power supply's minimum, and provide the normal voltage. This saves the power supply from the most severe brownouts under which it would still continue to operate.

Below the minimum

Not all brownouts are controlled. Even when they are, if you're in an area where the power infrastructure is woefully inadequate for demand, voltage can drop below the power supply's minimum. When this happens, the result is the same as losing power entirely, the computer shuts down unexpectedly. You lose unsaved work, and your system can be left in a corrupted state. A UPS protects against this.