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New Gear: Eaton 9130 Dual Conversion UPS

We have a pair of UPSs here; one in the office and another in the house. In both cases, they run the network core; Ethernet switches, Wi-Fi access points, IoT hubs and the like. Our reliance on power-over-ethernet means that there are actually quite a lot of gear that’s on the UPSs.

For many years the UPS in my office was made by Belkin. It was cheap. It did the job, sustaining the network core through many a minor outage. Being fanless, it was silent…which I deeply admire.Eaton 9130 2UHowever, as with most low-cost UPSs, it was “line-interactive” design. In such a design the power provided by the batteries and invertor is connected in parallel to the utility power. When utility power falters the local circuitry tries to make up the slack. The design is simple. Any UPS under $500 new is almost certainly a line-interactive design.

More sensitive gear is better served using a more sophisticated design known as “online” or “dual-conversion.” An online UPS puts its active circuitry between the utility power and the load. The utility power is turned into DC, which feeds the batteries and the invertor, which makes brand new, pristine, stable AC power for the load.

The switching is all done at the DC layer. When utility power fails the invertor keeps merrily chugging along using DC from the batteries. The load never sees any change in delivered power. Not even a line switch.

Online UPSs are standard fare in data centers, but more costly than a typical home office dweller could justify.

Welcoming Mr. Eaton

In the Great Texas Freeze of February 2021 I learned that our UPSs did not like generator power. Nor did our American Standard gas furnace. This made me reconsider another round of batteries for the elderly Belkin UPS. Instead, I’ve opted to replace it with a new Eaton 9130 online UPS.

This device is technically new-in-box, unsold inventory, even though the 9130 is officially past end-of-life. I’m told this is because some of the parts used in its manufacture are no longer available. So, Eaton replaced the old 9xxx series with the newer 9SX Series. They are largely cosmetically different, their internals only slightly updated.

These devices are very long-lived. My Belkin is over around 14 years old, having seen seen several sets of batteries over the years. I found used Eaton 9xxx series available from electronics recyclers on E-bay. The one I thought a particular bargain is a 9130 2RU model rated for 1KVA. It was just $100 + shipping, without batteries.

Given its age, even new-in-box, the original batteries would have been badly degraded. In truth, the devices requires three batteries that can be found for just $30 each!

EBP-1605 Compatible Replacement Battery PackBut I needed the wiring harness, too. It was easier to buy the EBP-1605 Compatible Replacement Battery Pack via Amazon for $199. So, for around $350 I have a proper, online UPS, new-to-me, for my network core.

Let’s Make Some Noise!

With the new battery pack installed I fired the unit up on my bench. As Karl Fife had warned me, the cooling fan made quite a roar. The original fan, a 12 vdc model from Sanyo Denki, is rated for 24 dBA.

Sanyo Denki 9A0824G401

Rather than accept this disturbance in my otherwise blissfully silent home office, I ordered an 80mm Noctua Ultra Quiet fan to upgrade the UPS. It’s rated for 16.1 dB A noise level, which is much quieter. Basically silent.

Noctua NF-8FLX

Spinning at 2000 RPM, it’s markedly slower than the original fan. As a result, it’s rated for 50.4 m³/h air flow vs 55 m³/h for the original fan. Nonetheless, I am confident that it will suffice.

Tach vs Locked Rotor Signal

While both fans have three wire connections, they differ in how they use the third (yellow) lead. Noctua uses the third lead to send a tachometer pulse, so the host can know the fan speed. The original Sanyo Denki fan uses it for a “locked rotor signal” that get tied to v+ should the fan actually fail.

This mismatch in status signaling means that the UPS constantly thinks the fan has failed. So, it alerts, which defaults to including a loud beeping sound. Happily, the UPS configuration allows audible alarms to be defeated.


I started to write this post a couple weeks ago when Mr. Eaton arrived. The new battery arrived last week. Installation was easy. The fan arrived earlier this week and is now installed. In fact, earlier today I swapped Mr. Eaton into service.

Using the LCD panel and buttons on the front of the device I’ve been able to determine that the UPS is seeing 69 watts of load, which corresponds to 7% of capacity. This reflects the limited set of devices that constitute the network core; POE switch, cable modem, router, Algo SIP door phone, and various small POE-powered devices.

Karl also tipped me to the two different modes of operation: (1) Online and (2) High-Efficiency. Set via the front panel menu, this basically allows the UPS to toggle between online and line-interactive  modes. In high-efficiency mode, it operates as line-interactive. If there’s any anomaly with the utility power it automatically changes to online mode. This is supposedly easier on power consumption and battery life.


I kinda wish I had the optional network monitoring & management card. That’s beyond the budget for the project. At least for the moment.

Eaton 9130 NIC

The 9130 has onboard USB and serial interfaces allowing remote monitoring. Eaton provides a UPS Companion application. I may try monitoring using NUT, which can be installed as a extension on the Raspberry Pi4 running Home Assistant. USB is possible, since the PI has the requisite port and the devices are located in the same short rack.


Mr. Eaton seems to be happy in his new home. He’s a nice upgrade from the old Belkin UPS.

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