Transient (Voltage Spike)

A transient, often called a voltage spike or surge, is a very short, sharp deviation from the normal voltage waveform. IEEE 1159 splits transients into two types. An impulsive transient is a unidirectional spike, positive or negative, that rises and falls in microseconds, such as the disturbance from a nearby lightning strike or electrostatic discharge. An oscillatory transient swings rapidly above and below normal voltage in a damped ringing, typically from switching events like energizing a capacitor bank or breaking an inductive load. Both are over before a single AC cycle completes, which is exactly why they slip past protection designed for slower faults.

Magnitude and duration

Transients can range from a few volts to several thousand volts and last from under a microsecond to a few milliseconds. A classic impulsive test waveform, the 1.2 by 50 microsecond impulse, rises to peak in 1.2 microseconds and decays to half-peak in 50 microseconds. Despite their brevity, the high instantaneous energy can puncture insulation and destroy semiconductor junctions. Damage is also cumulative: repeated small transients degrade MOSFETs, rectifier diodes, and input capacitors long before anything fails outright, which is why a machine can die weeks after the storm that actually wounded it.

Where they come from in a mining context

Lightning is the dramatic source, but the routine ones are self-inflicted: contactors switching banks of machines on and off, motors and compressors starting, upstream utility capacitor banks energizing at dawn, and neighbouring industrial loads. A hashcenter full of switch-mode power supplies both suffers and generates switching transients, so layout matters: shared circuits couple one machine's event into another's input stage. In a home deployment, the miner often shares a panel with heat pumps, well pumps, and welders, all classic transient generators.

Protecting mining hardware

ASIC power supplies and control boards are vulnerable to transients that exceed their input clamping. Defense works in layers. A service-entrance surge protective device (SPD) takes the bulk energy; point-of-use protection catches what remains; and the metal-oxide varistors inside a quality PSU clamp the last volts. Proper bonding and low-impedance grounding matter as much as the devices themselves, because a surge protector can only divert energy somewhere if that path exists. MOVs are sacrificial, they degrade with every hit, so SPDs with status indication should be checked after storms. On the repair bench, transient damage shows up as shorted input-stage FETs, cracked MOVs, and dead PSUs on machines whose hashboards are otherwise healthy; if that pattern sounds familiar, a repair assessment is cheaper than a replacement unit.

Transients in the power-quality picture

Unlike a voltage swell, which lasts cycles, a transient is a sub-cycle event, and unlike harmonics it is episodic rather than continuous. All of them belong to the same power quality picture an operator should monitor. A power-quality logger that captures waveforms, not just RMS values, is the only way to actually see transients; RMS meters average them into invisibility. For a fleet owner, unexplained clusters of PSU and control-board failures on particular circuits are the classic signature that transients, not bad luck, are eating the hardware.

The practical checklist is short. Put a rated SPD at the service entrance and verify its status indicators seasonally; keep miners off circuits shared with motors and compressors where possible; make sure the grounding electrode system is intact, since every clamping device depends on it; and if a site keeps eating power supplies, log the waveform before replacing the third unit. Transients are invisible to the eye and to most cheap meters, but they leave fingerprints in failure patterns, and reading those fingerprints is cheaper than buying hardware on a schedule set by the local utility's capacitor bank.