A UPS for a mining rig: do you need one, which type, and when it pays off

The grid flickers for a second — and the rig sits silent until morning because you were asleep. A familiar story, and it is exactly what sells UPS units for farms. But a UPS under a rig is not obvious: its job differs from an office one, and the price of a mistake is a fried power supply. Let's go through when you need one, which kind, and when a protection relay for a tenth of the price is enough.

The short version (for the no-time-to-read)

A rig UPS exists to survive one-second flickers, not to "mine through an outage" — an hour of autonomy at 2 kW costs unjustifiably much.
Modern PSUs need a pure sine wave. A cheap UPS with "stepped approximation" may not save the PSU — it may kill it.
Volt-amps on the box are not watts. A "1500 VA" UPS usually holds about 900 W. Size by watts with a third of headroom.
Against surges and phase imbalance the answer is a voltage relay, not a UPS — and it costs times less. Often the right answer is the relay.
Autonomy beats the battery: if the rig returns to work by itself after a flicker, half the reasons to buy a UPS disappear.

What actually threatens a rig from the outlet

Household power has four problems, and they have four different fixes:

Flickers (0.1–2 seconds). The most common one. For a rig that is a full stop: the miner dies, the system may reboot. The damage is not "a second" — it is hours of downtime if you are not around.
Sags. Voltage drops for minutes to hours (evening peaks, old grids). A PSU with a wide input range survives it but runs hotter.
Surges and spikes. Lightning, a neighbor's welder, switching in the panel. They hit the power supply directly — and through it, the cards.
Full outages. Here a UPS only helps to bridge the pause: 5–10 minutes is enough to wait out the return of power or shut the rig down cleanly.

Note: three of the four are not about "a long blackout". That is what drives the choice.

UPS types, and why watts ≠ volt-amps

Off-line (standby). The cheapest: the load runs straight off the grid, switching to battery in 4–10 ms. A modern PSU usually rides through that switch, but the output waveform is stepped — and a PSU with active power-factor correction (nearly every decent one) may drop out or wear faster.
Line-interactive. The same plus sag correction. A reasonable minimum for a rig — provided it outputs a pure sine on battery.
On-line (double conversion). The grid is rebuilt from scratch at all times: no switching at all, perfect output. The right choice for a farm — priced accordingly.

Separately, on ratings. The box says volt-amps; a UPS's watts are usually 0.6–0.7 of the VA figure. "1500 VA" means roughly 900 W of load. A 1.5 kW rig needs a 2.5–3 kVA pure-sine unit — real money. That is exactly why large farms rarely put everything on a UPS: the system and the router go on the battery, and the cards ride out flickers thanks to a fast automatic restart.

Honest economics and the alternatives

Before buying an on-line UPS priced like a graphics card, count what you are actually insuring. A monthly flicker discovered in the morning is a night of downtime. If the rig picks itself up when power returns and is back on proven presets within minutes, the damage from a flicker shrinks to those minutes — and the expensive UPS stops paying for itself.

A voltage relay in the panel (or a protection outlet) — against surges and phase imbalance. Cheap, and it closes the most destructive scenario.
A small UPS for the router and the motherboard — notifications and control stay alive even when the cards go dark.
An on-line UPS for the whole rig — justified where the grid flickers several times a week and every minute of downtime is expensive.

On the wiring around the farm — outlets, cable gauges and breakers — we have a dedicated article, and on PSU headroom — the PSU article.

Where automation fits

A rig sitting silent after a flicker is the scenario that sells most UPS units. OCBot starts automatically after a reboot, restores the cards' proven presets, and reports to Telegram that the rig survived the outage and is mining again. The grid flickered — minutes later the rig is back at work, and you already know instead of guessing.

This article is general information summarizing public practice; equipment choice depends on your grid and load. OCBot is an independent project: not affiliated with NVIDIA, HiveOS or Hiveon. Use at your own risk — see the disclaimer.