Phase Imbalance When Mixing Miner Batches on One PDU
A facility in Ulsan called us after three breaker trips in one week on a 40 A three-phase feed. The operator had added Whatsminer M50 units to a row that previously held only Antminer S19s. Total wattage was within spec. The problem was phase distribution.
Why Mixed Batches Matter
Antminer PSUs draw slightly heavier on L1. Whatsminer units shift load toward L2. When six of each share a PDU, L1 runs 19% above L3. Korean industrial breakers tolerate brief imbalance but trip on sustained deviation above 15% on any leg.
Diagnosis Steps
- Clamp each phase at the PDU output during peak hashing.
- Record per-unit wall draw with a plug-in meter on each leg.
- Build a spreadsheet mapping unit position to phase load.
Rebalancing Without Full Shutdown
We schedule moves in two-hour windows per bay. Power down one bay, relocate two to three units to swap phase loading, power up, verify balance, move to the next bay. Total fleet downtime for the Ulsan site: four hours across two evenings.
Prevention
Standardise on one miner model per PDU where possible. If you must mix, alternate unit brands within the bay rather than grouping by batch arrival date.