Looking for a UPS Design That Doesn't Overheat Batteries

On Fri, 2 Jun 2006 09:45:40 +1000, "Cameron Dorrough" wrote:

"William P.N. Smith" wrote in message "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.
Don't Rotary UPSes just provide a few seconds of power while your diesel generators are firing up?
I'm sure some are configured that way - that would be a TPS (Temporary Power Supply). Although it takes a lot longer than a few seconds to run the flywheel down.
It depends what you buy. The Pillar UPS powering the Melbourne Stock Exchange (that's Melbourne, Australia - not Melbourne, USA) is rated for 30 minutes at full load.

When I had to re-engineer the power systems at a large govt computing centre here in Perth (Oz) we looked at several rotary systems. They all relied on the flywheel energy to cover the break until the backup diesel genset(s) start. One rather large bank's head office had this config with ONE diesel alternator. The outlook if it fails to fire is rather bleak.
I opted for three parallelled 300kVA UPS units, with inherent redundancy as we had a base load below 600kVA. I also added a third diesel set to the existing pair, bringing total diesel-generated output to ~1500kVA. Again, redundancy - and necessary capacity.
I don't "like" large battery banks, but I would never seriously consider a rotary storage system in any critical application. And I doubt there is a rotary offering in the O/P's 3kVA size.

budgie wrote:

On Fri, 2 Jun 2006 09:45:40 +1000, "Cameron Dorrough" cdorrough@nortonconsultants.com> wrote:
"William P.N. Smith" wrote in message
"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.
Don't Rotary UPSes just provide a few seconds of power while your diesel generators are firing up?
I'm sure some are configured that way - that would be a TPS (Temporary Power Supply). Although it takes a lot longer than a few seconds to run the flywheel down.
It depends what you buy. The Pillar UPS powering the Melbourne Stock Exchange (that's Melbourne, Australia - not Melbourne, USA) is rated for 30 minutes at full load.
When I had to re-engineer the power systems at a large govt computing centre here in Perth (Oz) we looked at several rotary systems. They all relied on the flywheel energy to cover the break until the backup diesel genset(s) start. One rather large bank's head office had this config with ONE diesel alternator. The outlook if it fails to fire is rather bleak.
I opted for three parallelled 300kVA UPS units, with inherent redundancy as we had a base load below 600kVA. I also added a third diesel set to the existing pair, bringing total diesel-generated output to ~1500kVA. Again, redundancy - and necessary capacity.
I don't "like" large battery banks, but I would never seriously consider a rotary storage system in any critical application. And I doubt there is a rotary offering in the O/P's 3kVA size.

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.
Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������

"budgie" wrote in message

Recovery after a discharge is a tradeoff. Do you want minimum recovery to (substantially) full charge to best position you for a possible follow-up outage, or a leisurely recovery which treats the battery properly?
The bad news is that you don't get to choose - the UPS manufacturers have made that decision for you and have opted for the over-zealous rate. This is usually compounded by an excessively high float voltage. To further shorten the life of the batteries, the regime is often one of current-limited (too high) constant voltage (also too high) charging. An example of a far better regime is set out in the data sheet for the Unitrode/TI UC2906/3906 SLA charge controller chips. Unfortunately - and yes, there seems to be only bad news - it is usually impossible to splice in a better charging system without causing the UPS' monitoring circuits to go apeshit.

Could you reformulate the above statements as a set of requirements I can put into a requirements document for a new UPS? I'm guessing that the requirements would be something similar to the following, but I am hoping you will make these statements more precise:
- UPS should use a recharge / recovery scheme that maximizes battery lifetime rather than minimizing recharge times, or should as a worst case allow this to be a user configurable option.
- UPS should use an appropriate float voltage for the batteries it uses.
- UPS should allow the use of deep cycle batteries.
- UPS should provide a way to use an appropriate topping charge every six months with the battery.

By the time one battery in a series string needs replacing, they all should be replaced. You create the exact situation you referred to above by replacing one of a series string.

If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I test each 12V and find that one is giving a good 12V reading when charged and the other never goes above 10V, why can't I just replace the dead 10V battery with a fresher 12V? How is replacing the dying battery promoting overheating?
-- Will

Will wrote:
...

If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I test each 12V and find that one is giving a good 12V reading when charged and the other never goes above 10V, why can't I just replace the dead 10V battery with a fresher 12V? How is replacing the dying battery promoting overheating?

You can replace only the bad one*, but expect short life from the one not replaced.
Jerry __________________________________ * You might even revive the bad one by floating it separately. Don't rely heavily on it, though. -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������

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.
After working with an electrician, I have a theory about why this is happening, and if correct, the theory suggests a different design for UPS systems that would avoid the problem. I am hoping some manufacturer has already implemented this idea and someone can refer me to their products.

This is a very complex problem and the best solutions are EXPENSIVE!
Well your industrial electrician should have first told you (electricity 101) that you need a PM( Preventative Maintenance) schedule on UPSes. This would involved thaking the UPS offline monthly/quarterly and testing the batteries and other portions of the UPS. The industrial size UPS all come with offers from 3rd party companies to perform PM on you UPS gear. If you buy cheap equipment, a quality 3rd party company (which will usually also sell you an extended warranty as part of the PM) will tell you to buy something industrial grade, like a 3-phase UPS that is interfaces to a Gen_Set.
Also I always design UPS systems, no matter how large, to have a 1:1 isolation transformer upstream of the all power feedeing the UPS. This eliminates most power quality problems from the local utility or the ass_hole down the street that is wreaking havoc on the electrical grid because he's using a 3phase welder and the idiot that run the utility commissions (here in the US) or elsewhere to not have the common sense to test/monitor and require such folk to put in equipment to mitigate the effects of certain types of industrial equipment on the electrical grid. (expensive equipment will allow you to monitor the power quality (or lack thereof) from you local electrical utility feed.

On all of the UPS systems we use generic "brick" batteries are joined together in a series, then the leads from the ends of these battery chains are connected to the UPS. The problem is that batteries rarely fail all together. If a 12V battery should be considered discharged and not useful at around 10V, and you have two 12V batteries joined in series, what happens when one of the batteries maintains a full charge at 12V but the other battery in the series starts to lose its ability to hold charge and slips below some critical level? From the point of view of the UPS, it doesn't see anything about the state of individual batteries. The UPS only sees that the total voltage of the two 12V batteries in series has fallen from 24V to 22V.
Maybe an electrical engineer can step in here and explain what is happening,

UPS batteries and battery charging circuits and semiconductors leave much to be desired. If you spend some time researching 'gel-cel' batteries and other types of batteries used in UPSes, you find there are subtle difference in the batteries. When these differences are combined with with poorly designed charging circuits are poorly chosen semiconductors in the charging circuitry, trade offs are made. These are compounded by subtle differences in the electrical characteristics of different batteries supplied from a variety of low_cost suppliers.
If you look at battery charging semi conductors, such as those provide my Maxim, you can read the data sheets for some really good/detailed discussions on a myriad of issues related to this complex problem.

but my pure guess is that to maintain the same power output, an increased amount of current probably has to flow through the batteries. That creates problems with heating for the "good" battery, which is still measuring 12V. Now that 12V is receiving too much current, overcharges, overheats, and at some point the casing of the battery starts to melt. I haven't done enough experimentation to determine if it is the good battery or bad battery that is overheating. To be honest, in such situations I have often seen evidence that both batteries start to melt. Perhaps this is nothing more than one battery being in physical proximity to the overheating battery and therefore gaining heat from its physical contact. The only thing that is common to all cases is that one of the two batteries has discharged and should have been replaced before the overheating event took place.
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.
Aside from increasing safety and utility of the monitoring system, such a design would allow much easier re-use of off-the-shelf batteries, improving ease-of-use in making battery changes and lowering cost. While I realize that APC in particular has no desire to make anything regarding batteries non proprietary, maybe some other vendor has a UPS design that puts a direct monitoring circuit on each individual 12V brick battery, thus avoiding the overheating problem I have described?
Any information on why this overheating takes place, how to avoid it, and any referrals to third party UPS products that employ a more robust design are appreciated.

Overheating is unfortunately a vestige of a variety of problems with this complex issue. Search and read as much of this information is available via googling the net.......
HTH,
James

Will wrote:

Does any UPS manufacturer make a unit that will do about 3000VA - rackmount or tower configuration - that will treat the batteries better and use less aggressive charging in favor of long battery life? And of those units, does anyone make a unit where the batteries are given enough space between them that overheating in one battery stays localized to that battery?

On smaller UPS systems ( less that 10,000 VA) I'd suggest you make sure the UPS vendor uses a 'ferro-resonant' transformer in the UPS. It is a big heavy iron core that will filter most power quality feed problems (particularly transients) out from the utility power feed, thus making the UPS more durable and less transient electrical effects that deteriorate the solid state components and the batteries in the UPS.
BEST use to make a 'Ferrups' but they sold out and you have to do your research as this sort of UPS will be larger, much heavier and definitely more expensive. Alternatively, you can get use cheap UPSes and get your electrician to install a big 1:1 (one to one) isolation transformer upstream of all of the upses in your facility.
If you get an industrial grade UPS as the vendor about 3rd party maintenance PM costs and extended warranties which include PM or do the PM yourself (if you are a qualified electrician)....
HTH,
James

wrote in message

Well your industrial electrician should have first told you (electricity 101) that you need a PM( Preventative Maintenance) schedule on UPSes. This would involved thaking the UPS offline monthly/quarterly and testing the batteries and other portions of the UPS. The industrial size UPS all come with offers from 3rd party companies to perform PM on you UPS gear. If you buy cheap equipment, a quality 3rd party company (which will usually also sell you an extended warranty as part of the PM) will tell you to buy something industrial grade, like a 3-phase UPS that is interfaces to a Gen_Set.

I called every APC UPS dealer in the San Francisco Bay Area and asked them to quote on a service to come in once each quarter and test batteries and replace them. They all basically said "Huh, what do you mean?" Most of the dealers appear to be nothing more than part ordering shops, and they don't understand the technology let alone provide preventative service for it.
I'm with you completely that a device like this needs a qualified technician to test batteries periodically, and I would be quite happy to outsource that to a qualified organization or person who specializes in battery and UPS systems. I honestly couldn't locate one in the South San Francisco Bay Area, and if you know of a few organizations or consultants that would be able to quote on this I would be glad to know about them. I can't see us spending much more than maybe $200/quarter on the activity, but my surprise was not about pricing but rather in not finding anyone who even seemed qualified to do the task.
-- Will

On Thu, 1 Jun 2006 19:31:20 -0700, "Will" wrote:

Could you reformulate the above statements as a set of requirements I can put into a requirements document for a new UPS? I'm guessing that the requirements would be something similar to the following, but I am hoping you will make these statements more precise:
- UPS should use a recharge / recovery scheme that maximizes battery lifetime rather than minimizing recharge times, or should as a worst case allow this to be a user configurable option.
- UPS should use an appropriate float voltage for the batteries it uses.

I avoid the word "should" in specifications. Unless you intend to scour responses with a fine tooth comb and solicit clause-by-clause statements of compliance, you are wasting your time. Even then, if the supplier states "comply" to a "should", it doesn't mean he actually DOES what you preferred. I "should" eat less fatty food, but I don't.
Focus on the recovery time, and maximum recharge current being less than (say) 60% of manufacturer's recommended max charge rate - the derating being for thermal reasons given that the MR figure will usually be free air rated.
Focus on float voltage being whatever gives about 85-90% S.O.C. Any higher and you WILL progressively cook the batteries.

- UPS should allow the use of deep cycle batteries.

?? Deep cycle vs SLA/VRLA. You need to decide on one battery type.
I'm not sure whether you are looking at the 3kVA size or not, so battery choice and ventilation are unknowns here. SLA's are widely used simply because they avoid ventilation issues.
I'm also not sure whether you are buying one or a hundred. Writing a spec for one is a bit of overkill unless it is BIG (50kVA or more), otherwise just keep the spec as purchasing guidelines to enable interrogation of wannabe suppliers.

- UPS should provide a way to use an appropriate topping charge every six months with the battery.

Not only pointless, but probably deleterious in gelled electrolyte types. See above re battery type.

By the time one battery in a series string needs replacing, they all should be replaced. You create the exact situation you referred to above by replacing one of a series string.
If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I test each 12V and find that one is giving a good 12V reading when charged and the other never goes above 10V, why can't I just replace the dead 10V battery with a fresher 12V? How is replacing the dying battery promoting overheating?

By the time one battery has died - unless we are talking of infant mortality - it's mates have been subject to the same regime of use/abuse, and should be replaced before they follow. You are creating a series string of unequals, which is a recipe for failure. It's almost like changing tyres one at a time, except with tyres you can at least see their condition. False economy.

Well, what about finding a motherboard with lower power consumption? I use the VIA C3 cpus because they only draw 8-10 watts.
My house in the woods got taken out by a brush fire; but before I used to run a 486 directly off the batteries. no ups, no AC power supply. I just center tapped two 12v and a 6v battery. Ran the 6 volt thru a silicon diode, which dropped the voltage to 5.3 vdc.
But you could get the ATX 3.3 vdc with 3 nicads in series, and the 5.3 vdc with a six volt, and run the two (+12vdc & -12vdc) straight off lead acid cells. maybe use a germanium diode to cut the full charge 12.7 back down to 12.3 which is within spec for the ATX.
Its gonzo more efficient than taking the DC from the battery bank and turning it into 110AC, then having the SMPS change it back down again into the DC the ATX jack wants.
BTW: I usta have telco RSU batteries; 259 pound 2.08 volt cells. THe voltage was a little low because the acid was watered down; the runtime was only 50%. But the result was that these cells, which had been manufactured in 1958, were still doing just fine. No *sulphation*. so- if you wanna quit worrying about dead cells, water them down.

On Thu, 01 Jun 2006 21:58:39 -0400, Jerry Avins wrote:

budgie wrote:
On Fri, 2 Jun 2006 09:45:40 +1000, "Cameron Dorrough" cdorrough@nortonconsultants.com> wrote:
"William P.N. Smith" wrote in message
"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.
Don't Rotary UPSes just provide a few seconds of power while your diesel generators are firing up?
I'm sure some are configured that way - that would be a TPS (Temporary Power Supply). Although it takes a lot longer than a few seconds to run the flywheel down.
It depends what you buy. The Pillar UPS powering the Melbourne Stock Exchange (that's Melbourne, Australia - not Melbourne, USA) is rated for 30 minutes at full load.
When I had to re-engineer the power systems at a large govt computing centre here in Perth (Oz) we looked at several rotary systems. They all relied on the flywheel energy to cover the break until the backup diesel genset(s) start. One rather large bank's head office had this config with ONE diesel alternator. The outlook if it fails to fire is rather bleak.
I opted for three parallelled 300kVA UPS units, with inherent redundancy as we had a base load below 600kVA. I also added a third diesel set to the existing pair, bringing total diesel-generated output to ~1500kVA. Again, redundancy - and necessary capacity.
I don't "like" large battery banks, but I would never seriously consider a rotary storage system in any critical application. And I doubt there is a rotary offering in the O/P's 3kVA size.
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.
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.
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.
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.
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).

"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?
-- Will

On 2006-06-01, 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.

a shorted cell could do that if you've batteries in parallel.

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. That creates problems with heating for the "good" battery, which is still measuring 12V. Now that 12V is receiving too much current, overcharges, overheats, and at some point the casing of the battery starts to melt.

It'd lots of power for that to happen. many UPSs only charge at a low rate...

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.

If a battery fails it's time to replace all of them either they failed early and it's possiblty a bad batch, or you've missed the due date to replace them.
Bye. Jasen

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."?

Sorry, State of Charge

?? 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?

I'd venture you're correct.

"Will" wrote:

If I take an older UPS gel-cell battery which is in series as 2 x 12V, and I test each 12V and find that one is giving a good 12V reading when charged and the other never goes above 10V, why can't I just replace the dead 10V battery with a fresher 12V? How is replacing the dying battery promoting overheating?

Ah, we've discovered the problem with your existing UPSen.
First, replace the batteries on a regular schedule, before they fail.
Second, battery strings must be matched, so replace all the batteries in a string at the same time.
Please note: You haven't specified your requirements very well. The answers for hundreds of kilowatts of UPS for a stock exchange and a few kilowatts for a local business are significantly different, and you are getting answers all over the map.

"Will" wrote:

I called every APC UPS dealer in the San Francisco Bay Area and asked them to quote on a service to come in once each quarter and test batteries and replace them.

You are asking the wrong folks. I'm not sure what to look for, but you want repair and PM, not sales.

I can't see us spending much more than maybe $200/quarter on the activity

Well, how many UPSen of what size are you talking about? I'd do 3 or 4 in the kilowatt range if you delivered them to my shop and picked them up a couple days later, and a service call would cost quite a bit more. I suspect a scheduled battery change regimen would cost you less money and provide better reliability.
[Not actually an offer, I'm on the wrong coast.]