Monday, 18 May 2015

UPSs tinkering

Doing a bit of tinkering with UPSs (Uninterruptible Power Supplies) for the FM station I help out at, and been discovering some interesting fact and details that I'm making note of, again more for my benefit that others probably!

Firstly, the problem. Several old UPS units well past their prime have been in use to smooth the power out and keep the equipment going for all those little blips in power, this is to provide power to an FM transmitter, audio processor and RDS encoder. All together they don't draw a huge amount of power (approx 130 watts), but I need them protected against surges and other nasties, also the power in our particular location isn't very good, drops out often and suffers from surges, brownouts and all sorts, so protecting this sensitive and expensive equipment is a must.

I've used a variety of APC, Belkin and no-name UPSs for this job, mainly ones I've salvaged and either got working enough by cycle charging them or pure luck, and they hold up for at least a few minutes in a power failure which smoothes out most of the dips we get. Now I had a chance to properly replace a couple, the first was my old ALC Smart-UPS sc420 which is a reasonably new model (4 years approx), and I didn't use as it was alarming about battery failure. So looking to purchase a new battery, hit the APC website and they wanted me to trade the whole UPS in for a replacement. This seems excessive, it only needs a new battery. So, all of these units are able to be replaced, taking the battery out, it's a regular sealed lead-acid (or gel, I'm not sure) battery. Looking it up, APC call it the RBC2 which is a single unit 12v battery. You can get replacements relatively cheap, in this case around the £25 mark including delivery, so that was a no-brainer, order that, swap the battery and off we go. Went well, and now using it's monitoring on my linux server (apcupsd) it's currently showing it's at 55% load capacity, battery at 100% and approx 16 minutes of run-time available. Excellent, so that solves the immediate problem.

I therefore now have a 'spare' UPS to tinker with, and this one has a bit more power behind it. This one is the APC smart-ups 1500, and after looking it up this can deal with 980 watts at max, so this is a pretty decent size unit (It's also quite heavy!), so again pulling it apart to see what batteries it has, and this one has two joined together. The pic below shows what configuration it has:

These are considerable larger batteries than the RBC2 units, and you can see there are two joined together. On the right terminals (the blue block) is a large fuse joining the terminals together, and on the left you see the cables that are connected into the UPS itself (the yellow marks are the adhesive that had covers over all the exciting bits). Taking it all apart, I'm expecting two 12v batteries again, so joining them in series like this would give a 24v pack. Each battery was registering around 2v on their own, and so seem pretty dead to me (This ups is probably more like 10 years old, and in my use it died probably 2yrs ago and has been left unplugged ever since, so I suspect sulphurisation has occurred and completely ruined them), so onto the next thing, identifying so I can replace. This isn't easy.
APC batteries are completely generic, no markings, or anything. I suspect they either burn, scrub or simply cover all markings showing voltage, current, etc, which makes it harder. Luckily most websites have direct lookups for these batteries, just put in the ups product and it'll tell you what size, etc. So that looks like the next plan, to order a couple, wire them up and get this UPS back on the road!

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