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Looking for a UPS Design That Doesn't Overheat Batteries
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repatch
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Joined: 02 Jun 2006
Posts: 9

PostPosted: Fri Jun 02, 2006 5:14 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:

Quote:
William P.N. Smith <news2006c@compusmiths.com> 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.

Quote:
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
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Jerry Avins
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Joined: 03 May 2005
Posts: 534

PostPosted: Fri Jun 02, 2006 6:00 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

repatch wrote:

Quote:
On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:

...

Quote:
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.
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nicksanspam@ece.villanova
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Joined: 26 Sep 2005
Posts: 35

PostPosted: Fri Jun 02, 2006 8:46 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

repatch <repatch42@yahoo.com> wrote:

Quote:
On Fri, 02 Jun 2006 07:45:03 -0400, nicksanspam wrote:

William P.N. Smith <news2006c@compusmiths.com> 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.

Quote:
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? :-)

Quote:
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 Smile 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
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jk
science forum beginner


Joined: 02 Jun 2006
Posts: 6

PostPosted: Fri Jun 02, 2006 9:07 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

"Will" <westes-usc@noemail.nospam> wrote:

Quote:
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
Quote:
That
creates problems with heating for the "good" battery, which is still
measuring 12V.
THe same current flows through both.



Quote:

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
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jk
science forum beginner


Joined: 02 Jun 2006
Posts: 6

PostPosted: Fri Jun 02, 2006 9:16 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

"Cameron Dorrough" <cdorrough@nortonconsultants.com> wrote:

Quote:
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.



Quote:
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.


Quote:

HTH,
Cameron:-)


jk
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jk
science forum beginner


Joined: 02 Jun 2006
Posts: 6

PostPosted: Fri Jun 02, 2006 9:18 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

"Cameron Dorrough" <cdorrough@nortonconsultants.com> wrote:

Quote:
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
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Peter Bennett
science forum beginner


Joined: 02 Jun 2006
Posts: 2

PostPosted: Fri Jun 02, 2006 9:48 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

On Thu, 1 Jun 2006 23:28:26 -0700, "Will" <westes-usc@noemail.nospam>
wrote:

Quote:
"budgie" <me@privacy.net> wrote in message
news:n8iv72tgf9kue7mhgaguvg5ciah6tj97mq@4ax.com...
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
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Peter Bennett
science forum beginner


Joined: 02 Jun 2006
Posts: 2

PostPosted: Fri Jun 02, 2006 9:48 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

On 2 Jun 2006 07:45:03 -0400, nicksanspam@ece.villanova.edu wrote:

Quote:
William P.N. Smith <news2006c@compusmiths.com> 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
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Will11
science forum beginner


Joined: 01 Jun 2006
Posts: 7

PostPosted: Fri Jun 02, 2006 10:26 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
news:8oa082laev3l0g698qa28gr212uk519k69@4ax.com...
Quote:
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
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William P.N. Smith
science forum addict


Joined: 23 Nov 2005
Posts: 56

PostPosted: Fri Jun 02, 2006 10:45 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

"Will" <westes-usc@noemail.nospam> wrote:
Quote:
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.
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Fri Jun 02, 2006 10:54 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

nicksanspam@ece.villanova.edu wrote:

...

Quote:
Spoken like a hide-bound bureaucrat Smile 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.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Fri Jun 02, 2006 10:59 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

Will wrote:

Quote:
"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
news:8oa082laev3l0g698qa28gr212uk519k69@4ax.com...

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.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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nicksanspam@ece.villanova
science forum beginner


Joined: 26 Sep 2005
Posts: 35

PostPosted: Fri Jun 02, 2006 11:07 pm    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

Peter Bennett <peterbb@nowhere.invalid> wrote:

Quote:
William P.N. Smith <news2006c@compusmiths.com> 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?

Quite well...

Got numbers?

Nick
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William P.N. Smith
science forum addict


Joined: 23 Nov 2005
Posts: 56

PostPosted: Sat Jun 03, 2006 1:04 am    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

nicksanspam@ece.villanova.edu wrote:
Quote:
Given a max charging current,
we could use these imbalances to predict the max temp rise.

But the meltdown doesn't come from charging current, it comes from
internal shorting of a cell quickly converting all it's stored energy
to heat.
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Will11
science forum beginner


Joined: 01 Jun 2006
Posts: 7

PostPosted: Sat Jun 03, 2006 1:35 am    Post subject: Re: Looking for a UPS Design That Doesn't Overheat Batteries Reply with quote

Out of curiosity, would there be a detectable temperature increase prior to
the shorting event within the battery? If you saw increasing internal
temperatures at a point in time (like night) when outside temperatures are
falling, might that be a clue that the battery's failure is imminent?

--
Will


"William P.N. Smith" <news2006c@compusmiths.com> wrote in message
news:jun182tbr5nq2tin60mi75s8evaksspo7d@4ax.com...
Quote:
nicksanspam@ece.villanova.edu wrote:
Given a max charging current,
we could use these imbalances to predict the max temp rise.

But the meltdown doesn't come from charging current, it comes from
internal shorting of a cell quickly converting all it's stored energy
to heat.
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