Looking for a UPS Design That Doesn't Overheat Batteries

[[email protected]]

[email protected] Gave us:
You're an idiot. Batteries, when delivering energy, do not exhibit
the same heat as that which they deliver the energy to (the load).

Care to explain that further?

Nick

 

[Floyd L. Davidson]

I doubt that.

With the type of battery strings I've seen it *never* happens
that one cell shorts, so it really isn't a problem. That is with
large lead-acid batteries. I don't know if it is more likely with
others or not.

We might somehow come up with a "dangerous" example of this kind, but
it seems to me that the electrical energy in a battery is insufficient
to raise its temp more than a few degrees. For example, a Diehard might
store 1 kWh (3400 Btu) and weigh 30 pounds. If it contained half water,
the temp rise might be 3400/15 = 226 F.

True. It isn't going to warm the battery up. The idea that one should
short a car battery on a cold day is *stupid*.

The water might boil, but it
seems unlikely to explode, even if every cell in the battery shorts at
the same instant.

Oh, it might well explode! Notice that big spark? Well that's
what sets off the hydrogen gases that do get a wee bit warmer
than any 3400 Btu stored in the battery can manage. It tends to
spill sulfuric acid on the idiot too.

 

[Roy L. Fuchs]

No. I'm sure about the first, and cold copper wire conducts more current,

No, it does not. A SUPERCOOLED copper wire MAY be less resistive,
but for ALL intents and purposes, we get the same wire in arctic
conditions that we get in a desert swill. As far as it taking more
current, it will heat up to the fuse point at MAYBE a slightly higher
current due to a lower starting ambient, but the reason isn't because
it conducts better.

but maybe cold bearings have more friction.

The bearings do not, but any greases on them are like putty.

Which part do you doubt, with
all your cold weather (Barrow, brrrh) starting experience?

The part that you posted.

 

[Roy L. Fuchs]

Care to explain that further?

Nick

http://en.wikipedia.org/wiki/Battery_(electricity)

 

[Floyd L. Davidson]

No. I'm sure about the first, and cold copper wire conducts more current,

With negligible effect though... we aren't talking about
absolute zero temperatures, just reasonable ones, say like -40.

but maybe cold bearings have more friction. Which part do you doubt, with
all your cold weather (Barrow, brrrh) starting experience?

At -40 the grease normally used is nearly solid. If it hasn't
been changed, the starter probably won't work at all.

Worse though, is that metals can sometimes simply break when
that cold if they are subjected to "shock".

 

[Jerry Avins]

Floyd L. Davidson wrote:

...

If the battery is in series with another battery, they must have
the same *current* ratings. That's it. ...

Nonsense! The batteries must also have the same ampere-hour capacity,
and ampere-hour capacity decreases with age and use. I suppose it's
possible to hitch a percheron and a pony, but a standard doubletree is
designed for a matched team.

Jerry

 

[Floyd L. Davidson]

Floyd L. Davidson wrote:

...


Nonsense! The batteries must also have the same ampere-hour capacity,

That simply is *not* true.

What is true is that you cannot safely exceed the ampere-hour
capacity of any battery in the string.

and ampere-hour capacity decreases with age and use. I suppose it's
possible to hitch a percheron and a pony, but a standard doubletree is
designed for a matched team.

Don't do battery plants much?

 

[Jerry Avins]

That 200Ah 6V battery might, for small values of 5.2




Believable numbers, consistent stories. I've read here that we might have
"a half-hour" to turn off a UPS with a swelling battery. Some claim the
problem is that energy in a shorted battery heats up the battery. How
would turning a UPS off stop such a battery from destroying itself?

It wouldn't. You have to remove the battery to a safe place. It will
rarely melt down in open air. You claimed the charging current melted
it. How silly! Even the fastest charge won't exceed rated discharge
current, and most will be a fifth of that or less. In the short term,
the energy for melt-down can't come from the charger. Where else then?

Others
say it's an overcharging problem (my favorite scenario.) Others say it's
a hydrogen problem. Then again, batteries lose heat to their surroundings.

Except as it affects case pressure, hydrogen is a red herring here.

Battery capacity drops with higher currents and shorter discharges.
A T-105 can supply 75 amps for 115 minutes, ie 862.5 Wh at 6 volts,
ie 2943 Btu. In yet another scenario, that might boil away 3 pounds
of water...

Your point?

Jerry

 

[Jerry Avins]

Wrong. Read what he wrote: "doesn't warm the battery enough".
That is true. Long before you get the battery warmer, you make
it deader!

Besides, shorting a battery to warm it is about the stupidest
thing I've ever heard of for other reasons, not the least of
which is the potential for an explosion that will make you
really really really ugly.

If it works, don't knock it. The attitude, "If I can't explain it, I
can't believe it" is more than a bit silly, don't you think? Back when
we had cold weather and ice skating on the local lakes, I used to keep a
kerosene lantern under the hood or a 60-watt bulb when a cold snap was
expected. The pliers were for when it was cold but not expected.

Jerry

 

[Floyd L. Davidson]

If it works, don't knock it.

If it *doesn't* work, do knock it. As stated, it will *not*
warm up the battery enough to make any difference.

The attitude, "If I can't explain it, I
can't believe it" is more than a bit silly, don't you think?

Yes, and I can't for the life of me understand why you continue
to espouse such a philosophy for battery plant engineering.

Back when
we had cold weather and ice skating on the local lakes, I used to keep a
kerosene lantern under the hood or a 60-watt bulb when a cold snap was
expected. The pliers were for when it was cold but not expected.

Just think, if you merely tried *starting* the vehicle,

1) it would start anyway, and
2) you would not be be risking your life.

You *can* trust that I've seen more vehicles started in the cold
without *any* sort of heat on the battery, and at temperatures
you've probably never come close to, than you can imagine. The
idea that you even needed more energy from the battery than it
was ready to supply is wrong to begin with.

 

[Jerry Avins]

http://en.wikipedia.org/wiki/Battery_(electricity)

Which paragraph?

jerry

 

[JoeSP]

Do you actually believe that the charging current is the culprit? Why
doesn't is affect new batteries? Put your thinking cap back on.

Jerry
--

Is there any other way for a battery to short internally, than when
lead-sulfide crystals build up on the plates? If other batteries are in
parallel, they too will short through that point.

 

[Jerry Avins]

Roy L. Fuchs wrote:

... A SUPERCOOLED copper wire MAY be less resistive,
but for ALL intents and purposes, we get the same wire in arctic
conditions that we get in a desert swill.

The thermal coefficient or resistivity in that range is 0.38%/degF. A
change from 120F in the Sahara to -40 at Point Barrow works out to about
2:1.

Jerry

 

[JoeSP]

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.

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,
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.

Here's a link I found, that might be useful, but since it was only cached, I
have pasted it here:

Designing cost effective critical back-up battery systems

Now an independent consultant in battery technology and marketing, Anthony
Green explains how there is no universal solution
A critical system is any system whose failure could threaten human life, the
system's environment or the existence of the organisation that operates the
system. Failure in this context does not mean failure to conform to a
specification but means any potentially threatening system behaviour. The
system should be resistant to failure and, if it does fail, it must be
fail-safe.
When evaluating a critical system it is important to look at the cost of
failure of the system. This is likely to be far greater than the cost of any
emergency back-up system, whether the cost is measured as a financial loss
or as a risk to human life. It could, therefore, be argued that the cost of
failure is so high that the investment cost of the emergency back up system
is not relevant and the security of the installation is the controlling
factor. However, this is not the reality and it is therefore important to
make an analysis of the risks and the costs to allow the right system to be
chosen.
Examples of critical systems are:
Communication systems such as telephone switching systems and aircraft radio
systems
Embedded control systems for process plants and medical devices
Signalling and information systems such as railway signalling, road networks
and runway lighting
Command and control systems such as air-traffic control systems and disaster
management systems
Financial systems such as foreign exchange transaction systems and account
management systems
Economically the requirement is to provide a cost-effective solution within
the requirements of the criticality of the system. This should be calculated
using life cycle costing as this is a technique which produces a spend
profile of a product over its life span. However, it must be recognised that
this economic calculation has to be for predictable life and failure
attributes. It cannot take into account the cost of an unexpected failure
and the consequential cost.
Reliable systems should be 'fault-free' systems where fault-free means that
the system's behaviour always conforms to its specification. Systems that
are fault-free may still fail because of specification or operational
errors. The costs of producing reliable systems grow exponentially as
reliability requirements are increased.
This is because of the use of more expensive development techniques and
hardware that is required to achieve the higher levels of dependability.
Increased testing and system validation is required to convince the user
that the required levels of dependability have been achieved
Batteries: reliability and economic characteristics
A battery is an electrochemical device and it has certain characteristics
resulting from this. Different electro-chemistries, lead-acid,
nickel-cadmium, nickel-metal-hydride, lithium ion, have different
characteristics, and even within these electro-chemistries different designs
and constructions give different attributes. All technologies have different
advantages and disadvantages and so an important activity is to find the
correct balance for the application.
The attributes of an electrochemical battery can be characterised as
relating to the critical aspects of the application and to the economics of
the system.
This is shown in Table 1 where the major attributes are listed and their
relevance to these two factors.
Reliability Factors
Reliability is based on the number of failure modes and their severity. The
measure of reliability is related to battery performance under the actual
operating conditions and a predictable failure mode is important for any
controlled maintenance regime.
If failure is regarded as the ability of the battery to meet the discharge
specification, then it is probably more important for the battery to
fail-safe than not to fail. In other words, the battery should avoid sudden
failure.
The most resistant of the existing technologies to sudden failure is
nickel-cadmium. Due to its metal plate structure an individual cell cannot
fail in open circuit, the worst-case failure being short circuit. This means
that a battery will not suddenly fail to perform. In the case of lead acid,
where the plate structure and active material are lead, open circuit failure
is possible. Thus to avoid a sudden battery loss it is necessary to use
parallel strings to ensure redundancy in the system. However, the cost
difference between lead acid and nickel-cadmium can still mean that the lead
acid parallel strings are the more cost effective solution.
Operation at high temperature or frequent cycling can cause certain failure
modes to become more prevalent and so reduce the reliability. These two
factors are important both with regard to the reliability of the system and
the economics.
Tolerance to over-charge and over-discharge and resistance to shock and
vibration are factors that can affect the reliability of the system and
cause failure modes not normally existing. Charging systems moving into
fault conditions or badly set up can cause over-charge and over-discharge
which can have serious consequences for some battery types. There are many
forms of mechanical abuse to which batteries may be subjected. While
stationary batteries are not normally subjected to shocks they may have to
tolerate vibration from rotating machinery, seismic loads and transport
during installation.
Economic Factors
Lifetime is a factor related entirely to the economics of the system. In
terms of reliability a two-year lifetime reliable battery is perfectly
acceptable provided it is replaced every two years.
Battery manufacturers sometimes quote design life and warranty life. These
have little bearing on real-life performance and it is important to use
actual service life under normal operation conditions.
Typical lifetimes under normal float conditions are shown in Table 2. The
longest established lifetimes, 20 to 25 years, are for thick plate lead acid
Planté cells and nickel-cadmium cells. Newer technologies have predicted
lifetimes of up to 20 years but have not been available in industrial
battery sizes long enough to be in real applications for this length of
time.
The lifetime of a battery has a large impact on a life cycle costing for a
system, as the cost of ownership of a battery system is much more than the
simple initial procurement cost.
In practice, unless the application discharges for longer than three hours,
does not endure any cycling, is in a temperature-controlled environment at
20°C to 25°C and does not have any specific requirements, it is unlikely
that the same kWh of battery support would be calculated for the different
technologies and plate types.
It is therefore important that battery sizing should be to a recognised
standard, the most well known of which are those produced by the IEEE which
has standards for sizing of industrial VRLA, vented lead acid and
nickel-cadmium batteries.
After the battery has been correctly sized, the only accurate way to compare
competing battery types is to perform a life cycle cost analysis. Such an
exercise considers all the costs associated with battery owner-ship over a
certain period of time, including the replacement of shorter-life batteries
and all associated maintenance and testing activities.
Examples of these costs are
Purchasing and administrative costs
Battery cost (initial and replacement, if applicable)
Transportation
Storage
Installation
Commissioning
Routine surveillance
Discharge testing to verify operability and predict end of life
Decommissioning and removal (if applicable)
Downtime cost of system shutdown during battery replacement
Disposal
Most of these costs can be quantified with some accuracy. However, the life
cycle analysis cannot calculate the cost of sudden and catastrophic battery
failure and this is no less important the predictable costs.
The shallow and deep discharge cycle life is related to the economics of the
system depending on the application requirements. The depth and frequency of
discharges to which it is subjected can limit the service life of a
stationary battery, so that it is less than the lifetime to be expected
under normal float conditions. Again, this is related to the technology, and
in a cycling application care must be taken to choose a product designed for
cycling applications and not simple float applications.
High temperatures have an effect on the lifetime of batteries, increasing
temperatures above 20oC to 25oC having the effect of reducing the lifetime.
This has a greater effect on lead acid batteries than nickel-cadmium
batteries but is, nevertheless, applicable to all electrochemical systems
due to the increased chemical activity.
Conversely, for temperatures less than 20oC to 25oC, there is a slowing of
the chemical reaction in a cell and result in a reversible loss of
performance. This means that, if the battery is required to give its full
performance at low temperatures, then it will need to be 'oversized' at
normal temperatures. Again this has a greater effect on lead acid batteries
than nickel-cadmium and differs between the various lead acid technologies.
Battery maintenance can have a significant effect on the economics of a
battery system, particularly when a remote or difficult site is involved and
so should be should be simple and not time consuming. It involves a variety
of tasks, including water additions (if applicable), voltage readings,
specific gravity checks, internal ohmic measurements, and connection
maintenance.
In open cells, the excess electrical energy absorbed by a lead-acid or a
Ni-Cd battery on float charge is converted to chemical energy through the
breakdown of water (electrolysis).
In VRLA batteries, the products of electrolysis are recombined to minimise
water consumption and eliminate water additions. However, this benefit comes
at the expense of battery life and reliability.
In vented batteries, water must be added periodically to compensate for
losses due to electrolysis and evaporation. The watering interval varies by
battery type and should be taken into account in maintenance calculations.
No universal solution
To paraphrase Abraham Lincoln, some of the points are applicable to all
applications, and all of the points are applicable to some applications, but
not all of the points are applicable to all of the applications.
What is important is to decide the priorities related to the application.
How critical is it? What is the cost of failure? How important is the cost
of implementation? Who makes the final decision?
There is no universal solution which can be applied to all applications.
Instead, it is necessary to fully aware of the requirements of the
application, be sure about its needs and choose a battery system that
satisfies those needs.
Email: [email protected]

 

[Jerry Avins]

If your car battery won't crank when it's -20F out, do what I do: short
the battery briefly by bridging the terminals with the handles of a pair
of pliers. The initial Short-circuit current won't be large at that
temperature, but the battery quickly warms up, so don't tarry. About two
seconds will raise the battery temperature to where it will crank the
cold engine just fine. Only a small fraction of the energy raised the
battery temperature 20F or so. Imagine the rise if all the energy went
to heat!

Try it. I doubt the battery will blow up or melt or swell.
How warm will it get?[/QUOTE]

I guessed up to about zero internally. All I really know is that the car
cranked fast enough to start after being shorted, but not before. It's
been 30 years since it was that cold around here. Successful
demonstration beats negative analysis every time in my book.

Jerry

 

[Jerry Avins]

You're an idiot. A wet cell type lead acid battery can most
certainly explode under short circuit conditions. Gel cells would
likely burst in their cases as well.

I've never seen or heard of a wet cell that spontaneously developed a
low-resistance internal short while significantly charged. Instead, they
develop high-resistance shorts -- due, I'm told, to sulfate bridging --
that disables them more-or-less quietly. Such abuse as shorting one with
pliers too long* can warp the plates, but even so, a separator would
also have to fail for a low-resistance internal short to develop. I
don't know what it is about the construction of gel cells that's
different, but something clearly is.

Jerry
_______________
*

 

[JoeSP]

If it works, don't knock it. The attitude, "If I can't explain it, I
can't believe it" is more than a bit silly, don't you think? Back when
we had cold weather and ice skating on the local lakes, I used to keep a
kerosene lantern under the hood or a 60-watt bulb when a cold snap was
expected. The pliers were for when it was cold but not expected.

I'm not sure the warming would happen in the cells when you short the
battery. Besides, in cold weather, the starter should provide all the load
necessary to do that on the first try. Theoretically, the starter should
crank faster on the second try if the battery is warmed. I don't recall
that happening in all my lengthy experience with lead-acid batteries and
cold weather.

 

[JoeSP]

Along with a nice big spark, you not only warm the battery but
you risk setting off an explosion which will douse your body
with sulfuric acid. With any luck you'll die, because you
probably don't want to live the rest of your life with the
effects of taking the acid bath...

I took an acid bath when I was about 9 years old. I was walking past a bank
of glass-jar batteries being charged and one blew up, showering me with
glass and sulfuric acid. It took about a minute for them to strip me down,
wash me off, and soak my clothes in water and baking soda. I didn't get any
in my eyes, so I didn't suffer any ill effects. The acid didn't burn my skin
or damage my clothes. I think the above paragraph might be a little
exaggerated.

 

[Floyd L. Davidson]

I took an acid bath when I was about 9 years old. I was walking past a bank
of glass-jar batteries being charged and one blew up, showering me with
glass and sulfuric acid. It took about a minute for them to strip me down,
wash me off, and soak my clothes in water and baking soda. I didn't get any
in my eyes, so I didn't suffer any ill effects. The acid didn't burn my skin
or damage my clothes. I think the above paragraph might be a little
exaggerated.

If you had been showered with full strength battery acid that
was not washed off for 1 minute, I assure you that it *would*
have burned your skin and damaged your cloths, to put it mildly.
(The clothes, incidentally, might not show a great deal of
damage immediately... but the next time they are run through the
washing machine they come out with more holes than not!)

From the description you give it would appear that the cell
which exploded was nearly discharged, and thus you were sprayed
with a mostly water solution. Damned lucky! Keep in mind that
even in relatively dilute form, if you had inhaled any
significant amount of it, the results would have been extremely
uncomfortable.

 

[Jerry Avins]

JoeSP wrote:

...

Is there any other way for a battery to short internally, than when
lead-sulfide crystals build up on the plates?

Warped plated can touch. Separators can disintegrate.

If other batteries are in
parallel, they too will short through that point.

You're right, of course, but it hadn't occurred to me. Parallel
batteries are as iffy as parallel diodes. Ballast resistors can force
load sharing, but that's lousy design.

Jerry