Uninterruptible Power Supply

Being a very technology-inclined person, electricity has an important role in much of my daily life. Many of my tools require it (I include computers in this category) and, when the power goes out, it is the absence of server noise that alerts me, not that of light. The best way to keep these devices running is with a UPS (see previous post on the subject).


Above is the “defender of the Internet” – this UPS keeps the modem, router, gigabit switch (and in passing, my amplifier) powered in the event of a power outage.

This UPS was $15 at a thrift store, is rated for 350VA (so… 275W?), and originally came with a 7Ah battery. Naturally, the battery was toast. I instead ran some wire from the terminals to a 12Ah battery from a broken car booster pack. Yes, I simply wrapped the wire around the terminal.

I haven’t tested the life span, however I once left it unplugged, with my amplifier playing music, for 30 minutes without failure. Boredom led me to plug it back in. I expect it should last several hours powering only the network.


The server has 8 hard drives, and consumes a fair amount of electricity (more than the small UPS can provide). Because of this, a much larger UPS is needed. While browsing Kijiji one day, it occurred to me that I’ve never checked there for a UPS before. It was a good thing I did this time:

Someone had a Powerware 5115 1400VA UPS for $15. The batteries were bad, of course, but it was able to provide a full load of 950 watts – more than sufficient for the server.

I picked it up, and discovered it had three 12V, 9Ah batteries in series, producing 36V @ 9Ah. I just so happen to have my trusty 36V SuperPak, which is made of six 12V 4.5Ah scooter batteries, for a total of, ahem, 36V @ 9Ah.

The SuperPak is contained in a video camera bag that just manages to hold all the batteries, and speaker wire is doubled up to carry the current. I’ve (temporarily?) inserted the wires into the female spade connectors exiting the UPS, however this probably does not provide the best conductivity (no heat issues though).

The Powerware 5115

This UPS generates a pure sine wave output. This is VERY nice for audio equipment, as there is no obnoxious hum that exits your speakers. The UPS, however, does make significantly more noise than the Internet UPS – aside from the cooling fan, which is louder than the whole server, a significant hum is generated when the UPS is operating on battery power. Ah well.

Like all UPSes, this one has a loud buzzer that kindly reminds you every 4 seconds that the power is out. It can be turned off for some error conditions, but others (such as battery low), it cannot. This simply doesn’t work in a house setting, so, simple enough, I desoldered the buzzer (just like with the Internet UPS).

It has 6 outlets in the back, coupled with RJ11/45 surge suppression, a console port to tell a connected computer of a power outage, and a convenient “Building Wiring Fault” light, that illuminates if hot/neutral are swapped, or ground is missing. In my case, there is no ground in my room : )

Power Handling

I connected my desktop and my monitor to the UPS to determine how long it could last using my SuperPak. I disconnected it, and as an initial test, I initiated a shut down on my desktop, to make sure the UPS could at least allow that.

It could not. I got 15 seconds of runtime before it cut off.

This is, of course, entirely due to my SLA battery pack being old (over 5 years old), and no longer packing the current handling it (may have) once had. My desktop is, however, a power hog (with dual graphics cards and 3 hard drives). But, if this is an indication of anything, it means that it will be inadequate for the server with these batteries.

Final Thoughts

I found a good deal online for three 12V @ 18Ah batteries, around $165 shipped. This will at least allow the server over 1h30 of runtime (according to the table in the UPS manual).

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Monday, January 9th, 2012 electronics, projects

3 Comments to Uninterruptible Power Supply

  • […] maybe not so quick. Tonight I was playing around inside the PW5115 UPS I wrote about here. Over the last several weeks it has been in service, I’ve run into a few problems with it, […]

  • Amy says:


    What size UPS would you recommend for a small business that has 1 server and 10 pc’s. Do I need to get a ups for each pc? Thanks!

    • Dan says:

      You are better off getting individual units for each PC, and a dedicated unit for the server. You would need a huge 3+ kVA unit to power all of that together, and the wiring would be a nightmare.

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