Single-phase online UPS
Single-phase online UPS
An online double-conversion UPS rebuilds its output continuously, so the load never sees a transfer, a sag or a spike from the utility. These are the systems for servers, network cores, medical and lab equipment, from 1 kVA rack/tower units to modular systems with N+1 redundancy.
Rack and tower
Online double-conversion with lead-acid batteries, at 120V, 208/230V and 240/120V.
Isolated
Online UPS with a built-in isolation transformer, for noise, ground loops and sensitive instruments.
Modular
The 4S, 6S and 12S add 6 kW hot-swap modules with N+1 redundancy in one frame; the 2S is a fixed 6 kW entry model.
Online lithium models (J90, J90i, P91 Li, P91g Li) are listed with the other lithium UPS on the single-phase UPS page →
How to choose
| If you need | Start with |
|---|---|
| Online protection for a server rack or network core, 1-3 kVA | P91 or P91g |
| A tower beside the equipment | T91 or T91i |
| 5-10 kW at 208V or 240/120V | P91 5-10k |
| Isolation for noisy power, ground loops or lab instruments, 3.8-10 kW | TX91 or TX91L |
| Below 3.8 kW with isolation | A UPS plus an isolation transformer after it |
| N+1 redundancy or room to grow, 6-48 kW | M90S family |
Frequently asked questions
What is an online double-conversion UPS?
It converts incoming AC to DC and back to clean AC continuously, so the load runs from the inverter at all times. When utility power fails there is no transfer, because the load was never on utility power to begin with.
When do I need online instead of line-interactive?
When the load cannot tolerate a transfer of a few milliseconds, when the utility power is poor (frequent sags, generator power, motor loads on the same service), or when the equipment is critical enough that you want the cleanest possible output.
What is an isolation UPS for?
An isolation transformer gives the load its own ground reference, which blocks common mode noise and breaks ground loops. The TX91 builds that transformer into an online UPS from 3.8 to 10 kW. Below 3.8 kW, pair a UPS with a separate isolation transformer connected after it.
Why choose a modular UPS?
Power modules are hot-swappable, so a failed module can be replaced without dropping the load, and one extra module gives N+1 redundancy. You can also start with the capacity you need today and add modules later instead of replacing the UPS.
Are lithium online UPS available?
Yes. The J90 and J90i are 1U online lithium UPS from 1 to 3 kVA, and the P91 Li and P91g Li are online lithium rack/tower units. They are listed on the single-phase UPS page with the other lithium models.