On Wednesday 26 March 2008 07:49:48 am John Summerfield wrote: > Tom Horsley wrote: > > On Wed, 26 Mar 2008 08:35:49 -0500 > > > > "David G. Mackay" <mackay_d@xxxxxxxxxxxxx> wrote: > > ... > > Most UPS boxes seem to be about the same. They'll be reporting > > self test OK and lots of battery life, then the power actually > > fails, and they fall over dead. > ... > Really all it has to go on is the potential difference between > positive and negative connectors. The electronics aren't going to > know how fast it goes from 72V (about where my UPS should be) to > something unsatisfactory without actually running it (partially) > down. While that's technically true, they could also use the age of the battery. Most (f not all) UPS batteries need replacing after 5-6 years, and decent modern UPS's allow you to set the date that you installed the battery. This is a fairly good indicator that the battery needs replacing. So they do have more to go on than the voltage. Unfortunately, they don't seem to use it, and this requires manual awareness and intervention. I bring this point up for the folks out there who have old UPS's and batteries, and are under the mistaken impression that their UPS is going to work the next time they lose power. I had to find this out the hard way, years ago, unfortunately. Hopefully someone else won't. Oh, and if you're buying a used UPS off of eBay, find out how old it is first. You might be able to buy it without the worthless battery, and save yourself some shipping cost, and possibly lower the price of the UPS. -dwight-
