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William P.N. Smith wrote:
... replace the batteries on a regular schedule, before they fail.
Sounds expensive, vs periodically testing and replacing any that don't pass the test.
Second, battery strings must be matched, so replace all the batteries in a string at the same time.
Sounds expensive. How well-matched must they be?
Nick
"Will" wrote:
Our company has had a long-standing problem where UPS batteries will at various points in their lifetime suddenly overheat, sometimes catastrophically to the point where the battery casing starts to melt and you can actually smell the gases from the battery leaking.
I wonder if you don't have a bit of confusion between cause and effect here. Old batteries can short a cell when the plates age (and swell) sufficiently, generating quite a bit of heat when the stored energy in that cell is released. This _can_ cause an avalanche effect in nearby cells and batteries, but the primary cause is ignoring the PM schedule on battery replacement...
budgie wrote:
...
Years ago, when wet cells were the only game, we ran a synchronous generator as a motor driving a flywheel. When power dropped, the contactor to the line did too, and a clutch engaged an internal combustion engine that ran on illuminating gas. The system never failed, but short dropouts -- they're more frequent than we had imagined -- were painful. Switching back to line power required that the generator be phase locked by hand before the contactor was re-energized. We couldn't let the flywheel carry the load while the contactor remained closed for the obvious reason.
Geez, Jerry, autosync has been around for ages.
So have I. :-)
In our configuration, the three gensets were (obviously) all initiated after the outage had lasted 15 secs. They were 2*300kVA and the added one was 900kVA. We used a PLC to set the rules: if the 300's were up and the 900 wasn't, they would attempt to parallel (autosync) off-load and then connect to the gen bus. If the 900 came up and the others weren't already on the bus (the usual case) it would connect, and the others would then abandon their off-load parallelling attempts and join individually.
We were a lot smaller than that, about 12 KVA, kludged together from war surplus equipment.
It took a bit of fine tuning to handle the dynamics of different sized machines, but it worked a treat. Worst case when all three fired was about 50 secs to have them all parallelled on load.
Great fun when you get it all working.
I have seen the in-line prime-mover, alternator, motor combos. My main issue with them was the frequency drop when the flywheel accelerated the prime mover up from 0 to 1500 (1800 your side?) rpm.
We have turbines at the sewage plant that run on Diesel fuel, with gravity feed from 500-gallon tanks indoors and the rest of the storage underground. They are set to wait 45 seconds before starting, and go on line 15 seconds later. It takes another minute or so for frequency to settle to spec, but not much cares. The pumps and aerators can wait a bit. The local power plant uses similar turbines to run their peaking generators, but they are on turning gear when idle. Ours can wait still.
The rotary that the big bank HO used was by "HH". It ran a controlled fluid coupling, with the flywheel at ~3000rpm. Once motor drive failed, as the flywheel decelerated the coupling was controlled so the alternator remained at line frequency. But you only had a finite (read *short*) time to get the prime mover(s) up. And really only one shot.
Our PM's were Detroit two-strokes. The 900kVA would be at speed within seven secs of the start of cranking - presuming it fired of course. But a failure to fire withing 30 secs would be the end of the bank (who also used a DD prime mover on their genset).
Jerry -- Engineering is the art of making what you want from things you can get.
On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:
William P.N. Smith wrote:
... replace the batteries on a regular schedule, before they fail.
Sounds expensive, vs periodically testing and replacing any that don't pass the test.
It is expensive, but you have to do it, since by replacing battery per battery you will end up with a string of unmatched batteries in various states of degredation. That's a perfect recipe for the symptoms you've described.
The NUMBER ONE rule of "battery packs" is strings of batteries must be replaced at the same time, no mixing and matching is allowed.
Second, battery strings must be matched, so replace all the batteries in a string at the same time.
Sounds expensive. How well-matched must they be?
Same date code is the only thing I'd be happy with.
TTYL
repatch wrote:
On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:
...
Sounds expensive. How well-matched must they be?
Same date code is the only thing I'd be happy with.
And, of course, same maker and model number.
It's simple, really. Once one cell in a team dies of old age, it's time to treat its buddies as honored veterans and put them out to pasture. Used individually instead of hitched as a team, they may have a useful contribution in a high-school lab or science club.
Jerry -- Engineering is the art of making what you want from things you can get.
repatch wrote:
On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:
William P.N. Smith wrote:
... replace the batteries on a regular schedule, before they fail.
Sounds expensive, vs periodically testing and replacing any that don't pass the test.
It is expensive, but you have to do it, since by replacing battery per battery you will end up with a string of unmatched batteries in various states of degredation. That's a perfect recipe for the symptoms you've described.
I haven't described any symptoms.
The NUMBER ONE rule of "battery packs" is strings of batteries must be replaced at the same time, no mixing and matching is allowed.
According to "solar consultant" George Ghio? :-)
Second, battery strings must be matched, so replace all the batteries in a string at the same time.
Sounds expensive. How well-matched must they be?
Same date code is the only thing I'd be happy with.
Spoken like a hide-bound bureaucrat :-) How about matching voltages within some range or equivalent series resistances? Given a max charging current, we could use these imbalances to predict the max temp rise.
Nick
"Will" wrote:
Our company has had a long-standing problem where UPS batteries will at various points in their lifetime suddenly overheat, sometimes catastrophically to the point where the battery casing starts to melt and you can actually smell the gases from the battery leaking. So far we have been lucky to catch such thermal events with temperature sensors but it has always been a goal of mine to better understand why this happens, and to find some UPS system where it can be avoided entirely. To date, we have seen these problems with APC Symmetra tower, Symmetra rackmount, and SmartUPS.
Maybe an electrical engineer can step in here and explain what is happening, but my pure guess is that to maintain the same power output, an increased amount of current probably has to flow through the batteries.
IN both charge and discharge, this is true
That creates problems with heating for the "good" battery, which is still measuring 12V. THe same current flows through both.
Regardless of the actual mechanism for the overheating we are observing, it seems to me that the obvious solution is to design UPS systems to physically connect to each 12V battery individually. Forget connecting multiple batteries in series, at least don't do that at the battery itself. By connecting to and monitoring individual batteries, now the UPS can see when an individual battery falls below some critical voltage threshold and put it into a special recharge state (not put any load on it). If the battery fails to recharge, the UPS can declare the battery defective and can signal the condition by an LED on the battery's compartment. If there is a network attached monitoring system, the UPS can send an e-mail.
What you want here is not that (Separate chargers for each battery gets expensive) but a cell/ battery monitor system. Such as Cell watch, or Alber.
"Real" ups systems use them all the time. jk
"Cameron Dorrough" wrote:
One idea that has been missed so far: If you are really serious about reliability (most UPS users aren't) and don't like dealing with batteries, consider installing a Rotary UPS. You'll find plenty of good info via a Google search.
BZZZT, won't work. Rotary UPS systems still use batteries, and still have all of the attendant problems. You are perhaps thinking of Flywheel UPS systems. THose, while they work for the VERY short term, give support in time periods measured in SECONDS, and require (on the ones I have worked on) several minutes to HOURS to recharge the fly wheel. They also have a low KW/KHW support per sq ft of consumed space in my opinion.
I know it's "old school" and more expensive initial outlay, but Rotary UPS's are used by the majority of the world's Stock Exchanges and major data centres for all of the reasons you mentioned in your post - and on power failure, they just work.
On all of the data centers I have worked on, only two had rotary UPS systems, and only one had a flywheel system. Certainly not the majority.
HTH, Cameron:-)
jk
"Cameron Dorrough" wrote:
One idea that has been missed so far: If you are really serious about reliability (most UPS users aren't)
Truer words were never typed. Amazing isn't it, how much money people will spend to ALMOST have reliable power to "Mission critical" systems.
jk
On Thu, 1 Jun 2006 23:28:26 -0700, "Will" wrote:
"budgie" wrote in message Focus on float voltage being whatever gives about 85-90% S.O.C. Any higher and you WILL progressively cook the batteries
What is "S.O.C."?
?? Deep cycle vs SLA/VRLA. You need to decide on one battery type.
I guess deep cycle would be a better choice for battery life, but probably requires a lot of additional cost and no one will support them in a smaller UPS?
Deep cycle batteries can be had as flooded cell, gel or AGM (gel and AGM are also known as SLA/VRLA.
I'm not sure that a deep cycle battery is the best type for a UPS, since a UPS will demand fairly high currents from the batteries when supplying power - as I understand it, deep cycle batteries are optimized for delivering low to moderate currents over a long period, and to survive many charge/discharge cycles. I would expect most UPS applications to have very few charge/discharge cycles (unless the power service is _very_ poor).
-- Peter Bennett VE7CEI email: peterbb4 (at) interchange.ubc.ca GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html Newsgroup new user info: http://vancouver-webpages.com/nnq
On 2 Jun 2006 07:45:03 -0400, nicksanspam@ece.villanova.edu wrote:
William P.N. Smith wrote:
Second, battery strings must be matched, so replace all the batteries in a string at the same time.
Sounds expensive. How well-matched must they be?
Nick
Quite well - since two batteries permanently connected in series are acting as a single battery, all cells will have the same "life experience". Chances are that when one cell fails, most of others are nearing end-of-life.
-- Peter Bennett VE7CEI email: peterbb4 (at) interchange.ubc.ca GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html Newsgroup new user info: http://vancouver-webpages.com/nnq
"William P.N. Smith" wrote in message
I wonder if you don't have a bit of confusion between cause and effect here. Old batteries can short a cell when the plates age (and swell) sufficiently, generating quite a bit of heat when the stored energy in that cell is released. This _can_ cause an avalanche effect in nearby cells and batteries, but the primary cause is ignoring the PM schedule on battery replacement...
When testing batteries, is there some key sign that might disclose imminent failure of one of the 12V bricks? Would we for example see the voltage decline in a non-linear way as it declines from 12V to 10V?
-- Will
"Will" wrote:
When testing batteries, is there some key sign that might disclose imminent failure of one of the 12V bricks? Would we for example see the voltage decline in a non-linear way as it declines from 12V to 10V?
You might notice a decrease in capacity, but since they are gelled batteries, you aren't going to be able to watch the voltage on individual cells or test the specific gravity of the electrolyte, so your best bet is (quick, cover your ears!) to replace them on a regular basis to avoid end-of-life phenomena.
nicksanspam@ece.villanova.edu wrote:
...
Spoken like a hide-bound bureaucrat :-) How about matching voltages within some range or equivalent series resistances? Given a max charging current, we could use these imbalances to predict the max temp rise.
Only if you know that the internal construction of each unit is the same. Cells are designed specifically to hide any symptom of sulfation for as long as possible, The laudable goal is building a cell that behaves as much like new as long as possible. Eventually, it falls apart quickly.
Jerry -- Engineering is the art of making what you want from things you can get.
Will wrote:
"William P.N. Smith" wrote in message
I wonder if you don't have a bit of confusion between cause and effect here. Old batteries can short a cell when the plates age (and swell) sufficiently, generating quite a bit of heat when the stored energy in that cell is released. This _can_ cause an avalanche effect in nearby cells and batteries, but the primary cause is ignoring the PM schedule on battery replacement...
When testing batteries, is there some key sign that might disclose imminent failure of one of the 12V bricks? Would we for example see the voltage decline in a non-linear way as it declines from 12V to 10V?
Back in the days of six-volt car batteries, they tested individual cell's short-circuit current. Anything less than 250 amps indicated immanent failure.
Jerry -- Engineering is the art of making what you want from things you can get.
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