Sealed lead acid battery maintenance?
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From: Cydrome Leader on 3 Jun 2010 13:23 In sci.electronics.basics John Tserkezis <jt(a)techniciansyndrome.org.invalid> wrote: > Martin Brown wrote: > >> And it is at least worth the occasional visual inspection of the >> batteries for obvious signs of swelling and distortion of the case. > > Unfortunately, that's not an effective enough test. Most fail at end > of life looking like new. So a visual test alone is not enough. > > Some of the large commercial scale units perform an internal battery > test with a limited load, with the marketing blurb claiming it's good > enough to detect a dud battery even while the unit is live and running, > never having to go offline for the test. I've chatted with and watched quite a few large (tens to hundreds of kVA) UPS maintenance techs. the standard procedure seems to be a visual check, retighten all connectors, measure voltage across all batteries, then again with the UPS in test mode where there is a real load across the batteries. They can usually spot a bad battery before it would cause problems. larger UPSes have redundant strings of batteries so even with a dud you can still operate.
From: terryS on 9 Jun 2010 16:43
On Jun 3, 3:23 pm, Cydrome Leader <prese...(a)MUNGEpanix.com> wrote: > In sci.electronics.basics John Tserkezis <j...(a)techniciansyndrome.org.invalid> wrote: > > > Martin Brown wrote: > > >> And it is at least worth the occasional visual inspection of the > >> batteries for obvious signs of swelling and distortion of the case. > > > Unfortunately, that's not an effective enough test. Most fail at end > > of life looking like new. So a visual test alone is not enough. > > > Some of the large commercial scale units perform an internal battery > > test with a limited load, with the marketing blurb claiming it's good > > enough to detect a dud battery even while the unit is live and running, > > never having to go offline for the test. > > I've chatted with and watched quite a few large (tens to hundreds of kVA) > UPS maintenance techs. > > the standard procedure seems to be a visual check, retighten all > connectors, measure voltage across all batteries, then again with the UPS > in test mode where there is a real load across the batteries. > > They can usually spot a bad battery before it would cause problems. > > larger UPSes have redundant strings of batteries so even with a dud you > can still operate. The telephone industry has been using vented lead acid batteries for decades; and has very precuise instructions for charging and then maintaining the 'maintenance' or float voltage. Also checking for discrepancies between individual cells. Mostly telecomm. batteries are 'floated' so that they are sitting there neither charging or discharging ready for instant use if/when the power fails. So while most auto and similar batteries will charge at anything up to a voltage of 2.33 volts per cell (that's 14 volts for a so called, six cell, 12 volt auto battery) and be completely discharged at just below 2.00 volts per cell ( 11.9 volts for auto) the telecommunications batteries are carefully floated at ether 2.15 volts or 2.17 volts per cell, dependent on which administration e.g. ATT or UK Telecomms. and whether the battery cells are Lead-Calcium or Lead Antimony construction. As said; you can ruin a battery by overcharging it (have seen them boiled dry) and or leaving them in a discharged state for long periods of time. Heat is also a factor, under the hood of a motor vehicle in hot climate being one of the worst environments. In some parts of the Middle East auto batteries sometimes last only a couple of years; whereas in a cool climate with light use our Nissan pickup battery is already 8 years old and may not have to be replaced yet, even next winter! UPS batteries are also floated; but when they are needed they are probably discharged aggressively for relatively short periods of time to operate inverters etc. |