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Looking for a UPS Design That Doesn't Overheat Batteries

J

Jerry Avins

Floyd said:
That simply is *not* true.

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

That's true only if you monitor individual battery voltages. (You can't
get at the cells.) In practice, the only measurement is of the total
voltage across the string. The batteries must be matched to support the
assumption that all voltages are the same and can be known from the sum.
Don't do battery plants much?

We're discussing UPSs, not battery plants in general. Typically,
"periodic maintenance" amounts to response to failure.

Jerry
 
N

no one that you know

Untrue. Take a look at some capacity vs temp curves. Warming a fully-charged
cold battery can increase the available capacity, releasing more than
the energy used to warm it.

Nick

And warming up a pair of pliers is just stupid and a waste of reserve cranking
amps...........when it's minus 40 I just hit the key and hold it even if it
doesnt crank very good at first it will. 99 times out of a hundred it allways
starts the car.
I got allot of practice at this I never plug my beaters in.
If it fails me more than two or three times I fix the car or get a new beater.
 
J

Jerry Avins

Floyd said:
...



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

I tried it as a skeptic, and it worked for me. Have you tried it?
Yes, and I can't for the life of me understand why you continue
to espouse such a philosophy for battery plant engineering.
???



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

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

Procedure: (1)Get into car, turn key, press starter button. (2)Hear
starter groan to no effect. (3) Get out, open hood, short battery, close
hood. (4) Repeat 1. (5) Hear starter rather more sprightly. Most times,
car starts.

That old Ford had a six-volt battery. Do you suppose that makes a
difference?
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.

I don't doubt that at all.

Jerry
 
J

Jerry Avins

JoeSP said:
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.

Lye is worse, but you still have a couple of minutes to rinse off. Eyes
excepted.

I use sulfuric acid as a pickle when soldering silver, with a rinse bath
near by. For delicate pieces that I don't want to grab with tongs
(copper to avoid electroplating) I use my fingers. No ill effects if
rinsed in a minute or so. I use muriatic acid to clean copper and brass,
and as a flux for soldering galvanized iron. I also dunk my hands in it
to reveal any small skin breaks that would warn me not to handle
cyanide. (When a cyanide bath is available, it's handy for lightening
nitric-acid stains from skin, but one wants assurance that the skin
isn't broken.)

Jerry
 
W

William P.N. Smith

Doh. I read that off the Trojan spec sheet, without bothering to do
the math myself, and without untangling the pointer to the fact that
they are talking about a string of 6 of them (36V). Div 6, really
small values of 5.2. 8*|
 
Roy L. Fuchs said:
No, it does not...

It does indeed, with a positive copper tempco:

RHOt = 1.8x10^-8(1+0.0039(T-20) ohm-meters at T(C).
The bearings do not, but any greases on them are like putty.

Cold bearings probably have less friction. Most cold things shrink,
so tolerances would increase. Warming engine oil helps, but that's
a different story.

Nick
 
J

Jerry Avins

Ah, rarely :)




I made no such claim.

Somebody did; I thought it was you. The OP, probably. He certainly
implied it in the starting message.

Jerry
 
J

Jerry Avins

It does indeed, with a positive copper tempco:

RHOt = 1.8x10^-8(1+0.0039(T-20) ohm-meters at T(C).




Cold bearings probably have less friction. Most cold things shrink,
so tolerances would increase. Warming engine oil helps, but that's
a different story.

The steel shaft probably shrinks less that the bronze bushing it rides in.

Jerry
 
D

Duane C. Johnson

i Roy;

Roy L. Fuchs said:
Nick Pine <[email protected]> Gave us:
No, it does not. A SUPERCOOLED copper wire
MAY be less resistive,

Maybe less resistive???
Wire resistance is close to the definition of
temperature.

The electrical resistance changes fairly linearly
from 0 ohms at 0 deg K.
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.

Of course it does.
As the shunt resistance approaches 0 ohms a greater
percentage of the power will be dissipated in the
battery resistance.

Duane

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Duane C. Johnson said:
As the shunt resistance approaches 0 ohms a greater
percentage of the power will be dissipated in the
battery resistance.

Wow, somebody agrees with me :)

The Exide site says their ORB78DT84 auto battery can deliver 770
"cold cranking amps" for 30 seconds at 0 F at 1.2 volts per cell,
ie 7.2 volts at the terminals. That makes the internal resistance
about (12-7.2)/770 = 0.00623 ohms... 770^2x0.00623x30/3600x3.412
= 105 Btu, which might warm the battery up to 0+105/15 = 7 F...

Nick
 
Y

Yankee Lima

Will said:
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.

Well i dont 've much idea abt UPS specifications but im using one of
locally made ups 24V, 1.5KW backed up by 2 acid batteries of 200 A
each. It gives me backup time for abt 8 to 9 hours continuously. Im
from Pakistan. where we 've Electricity load shedding more often...
I've faced no problem of overheating batteries...
 
R

Roy L. Fuchs

If it works, don't knock it.

It doesn't "work", dufus.
The attitude, "If I can't explain it, I
can't believe it" is more than a bit silly,

Then explain it, since you can't... you are more than a bit silly.

Shorting out a battery DEPLETES its charge, nothing more.
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.

The lamp was and still is viable, though not much of a punch in
truly cold conditions.

The pliers is just plain silly, and totally ineffective.
 
R

Roy L. Fuchs

Roy L. Fuchs wrote:



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

As soon as the wire carries current, what is its temperature?

The ambient temp has NOTHING to do with the operating temp of the
wire at that point.

You are crazier than a friggin loon with your position on this.
 
R

Roy L. Fuchs

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

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.
[/QUOTE]

The problem is that you do not even know what you observed.
 
R

Roy L. Fuchs

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

Good for you. I HAVE seen batteries that have exploded.
-- 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.

It is a well established warning on wet lead acid batteries that
dead shorts can cause explosions of the battery.
I
don't know what it is about the construction of gel cells that's
different, but something clearly is.

The electrolyte medium is a gel as opposed to a liquid... D'oh!
 
R

Roy L. Fuchs

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.
Glass jar batteries? I would say that the sulfuric solution was
likely quite weak. If you get a high concentration splashed on you,
you WILL remember it, and you would change you view.
 
R

Roy L. Fuchs

And warming up a pair of pliers is just stupid and a waste of reserve cranking
amps...........when it's minus 40 I just hit the key and hold it even if it
doesnt crank very good at first it will. 99 times out of a hundred it allways
starts the car.
I got allot of practice at this I never plug my beaters in.
If it fails me more than two or three times I fix the car or get a new beater.


Holding the starter on while it is NOT cranking can damage the
starter in a matter of a few seconds. That is the only thing wrong
with what you have said. You should crank, and pause... crank and
pause. If the starter stops cranking, sure it passes current, but it
ALL passes through one winding in the starter, and the commutator bars
for that winding, as well as the winding itself can suffer greatly.
For one thing the heat generated causes the shellac on the mag wire to
liquify, allowing inter-winding shorts to occur.
 
R

Roy L. Fuchs

I tried it as a skeptic, and it worked for me. Have you tried it?

You do not know what you tried, nor did you observe the results
correctly enough to know what occurred.
 
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