Looking for a UPS Design That Doesn't Overheat Batteries

[budgie]

Back in the days when batteries were mostly considered a power source, and
ran 36 VDC lights and appliances, charged by a donkey engine or a
windcharger, it was part of regular maintenance to test each 2V glass-jar
cell with a hydrometer and an ammeter. When one was faulty, you simply
unbolted the lead bars, inspected the lead plates for sulfation and erosion,
replaced the electrolyte, cleaned the plates, and you were back in business.

That was certainly a valid and viable approach. As long as there is (also read
*can be*) regular maintenance checks at the 2V (sic) cell level, the arguments
in favour of replacing an entire string are fairly much negated. Unfortunately,
except in certain larger UPS systems with external single-cell battery banks
this tends not to be the case, and I'd be VERY surprised to see any extent of 2V
modules in a 3kVA rackmount UPS.

There was also a period in time when replacing one cell contents in a 12V
automotive six-pack was considered a viable practice.

 

[Peter Dettmann]

I rarely cross post this widely, but for this thread there was not a single
newsgroup that best covered UPS. Which specific newsgroups do you think
this subject didn't belong in, and why?

sci.engr.electrical.sys-protection is the most obvious one as the
question seems not to be a question related to power line system
protection.

Peter Dettmann

 

[Roy L. Fuchs]

sci.engr.electrical.sys-protection is the most obvious one as the
question seems not to be a question related to power line system
protection.

Peter Dettmann

What a wuss. Get over it, boy.

 

[no one that you know]

Ok now I step in.
Bullshit myth about the pliers across the post.
why would you waste that current as heat in a set of pliers when all you have to
do is crank it for a few sec and warm your frozen starter up as well

 

[no one that you know]

Wait a sec you do this lol I wish you were my neighbour........I would have all
my friends over for a laugh.

 

[Roy L. Fuchs]

Ok now I step in.
Bullshit myth about the pliers across the post.
why would you waste that current as heat in a set of pliers when all you have to
do is crank it for a few sec and warm your frozen starter up as well

Jerry Avins wrote:

Aside from being top posted like that of a retarded Usenet newbie,
IAWTP.

The best way to manage cold batteries is to have them on a trickle
charger all night. Even a warmer blanket works.

Shorting them actually uses up what charge is available and doesn't
warm the battery enough to make it crank harder.

It is total myth.

 

[Roy L. Fuchs]

Wait a sec you do this lol I wish you were my neighbour........I would have all
my friends over for a laugh.

He claims to be an engineer too.

Your only claim to fame is that you are a top posting Usenet retard.

http://en.wikipedia.org/wiki/Top-posting

 

[[email protected]]

I happen also to be an electrical engineer, and I diagree with YOU.

Oh yeah? Well, I have *TWO* EE degrees, and I disagree with YOU.

Nick

 

[[email protected]]

why would you waste that current as heat in a set of pliers when all you
have to do is crank it for a few sec and warm your frozen starter up as well

Because the pliers put more heat into the battery,
and the starter works better when cold.

Nick

 

[Roy L. Fuchs]

Oh yeah? Well, I have *TWO* EE degrees, and I disagree with YOU.

Nick

I don't even believe that you have one at this point.

 

[[email protected]]

Shorting them actually uses up what charge is available and doesn't
warm the battery enough to make it crank harder.

It is total myth.

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

 

[Roy L. Fuchs]

I doubt that.


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

Nick

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.

 

[Roy L. Fuchs]

Because the pliers put more heat into the battery,
and the starter works better when cold.

You're an idiot. Batteries, when delivering energy, do not exhibit
the same heat as that which they deliver the energy to (the load).

And no, a starter motor on a car does NOT work better cold.

We are not at absolute zero here, and anything up in the temperature
range we ARE at will NOT make one IOTA of difference to a DC fed high
torque motor. In fact, the cold starter is likely to be more
reluctant to turn, not less.

Do you always make shit up?

 

[[email protected]]

[email protected] wrote:

Or a T-105 might store 5.2KWHR (17KBTU) and weigh 62#.

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

What's it take to convince you?

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? 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.

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...

Nick

 

[[email protected]]

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?

Nick

 

[Floyd L. Davidson]

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!

You came for advice, and you got it from people with experience. If you
value your "logic" more than their experience, have it your way.

I've got more experience with cold weather starting in my little
toe that you do all totaled times 100.

The above claims about how to warm a car battery are *stupid*
beyond belief.

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...

 

[Floyd L. Davidson]

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.

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.

 

[Floyd L. Davidson]

Because the pliers put more heat into the battery,
and the starter works better when cold.

Wanna bet money on that?

 

[Nick Pine]

Wanna bet money on that?

No. I'm sure about the first, and cold copper wire conducts more current,
but maybe cold bearings have more friction. Which part do you doubt, with
all your cold weather (Barrow, brrrh) starting experience?

Nick

 

[Floyd L. Davidson]

Oh yeah? Well, I have *TWO* EE degrees, and I disagree with YOU.

If I followed this exchange correctly, you appear (despite the
inability to state your case) to be *correct*.

Why anyone would go to all that trouble for "matching" batteries I
don't know! It isn't necessary.

If the battery is in parallel with another battery, they must
have the same float voltage rating. That's it. A regular
charge voltage necessarily must be current limited at for the
lesser rated of the two batteries.

If the battery is in series with another battery, they must have
the same *current* ratings. That's it. Float voltage will
provide the same current to both, and that is what must be
correct. Otherwise the lower limit of which ever battery must
be regulated.

Replacing perfectly good batteries just because one cell in a
string is bad is a ridiculous expense for large batteries; and
not doing it is an equally waste of money for small batteries!
That doesn't require engineering, it's something a damned bean
counter can figure out with a spread sheet!