PW5115 UPS – Quick Post

Okay, maybe not so quick. Tonight I was playing around inside the Power Ware 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, and cracked it open in hopes of finding some answers (as well as to change the noisy fan for something quieter.)

I was experiencing two issues:

  1. Every couple of days, the fan will randomly turn off. This happened ever since I got it, and sometimes happened every 4 days, once a week, then it happened twice in two days.
  2. It was no longer capable of supporting the server when mains was removed.
For the first issue, although the silence was welcomed, and the server remained powered, my concern was that, if this wasn’t a design feature, the UPS may overheat. Indeed, it did get warm when left for half an hour. However, the moment mains would fail, the fan would resume active duty.
It was after a couple of weeks that the server would no longer remain powered with battery power. Before I only had 15 seconds of runtime – not a lot, but enough to handle flickers and short brownouts. Now it tries to keep the server going, you can hear the hum inside when mains is cut, but the server simply dies.
I tested output voltage to make sure it was around 120VAC, and measured 117VAC. I then tried powering a smaller load, my laptop, which had no issues powering up.

When I opened it, there was nothing out of the ordinary. No bulging caps of anything of the sort. I believe at this point I can attribute the problem to aging, ready to retire batteries.

This is the huge bus capacitor at the 36VDC input. It has enough power that, when the batteries are disconnected, it can fire several relays and hold them for a second, before finally dying. As well, when the battery pack is connected initially, considerable current is sucked to charge this cap, enough that a large blue arc appears, creating ozone and smoke. Awesome.

Here you can see where the buzzer used┬áto be, removed to preserve my sanity. I don’t know if any of you have a UPS (or two) in your bedroom, but they will beep, non stop, for no reason. Power failed? Beep every 2 seconds. Battery dying? Beep continuously. If a power outage happens at 3am, this is not a sound you want to be woken up for. It has happened to me, and the adrenaline rush is actually kind of unpleasant.

To the top right of the buzzer footprint you can see a black-red-yellow wire. This is the wire going to the fan. I plan on replacing the stock turbine with a much quieter CPU fan. The turbine didn’t really even move that much air, anyway.

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Monday, January 30th, 2012 electronics 2 Comments