Looking for a UPS Design That Doesn't Overheat Batteries

[William P.N. Smith]

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.

 

[Jerry Avins]

[email protected] wrote:

...

Spoken like a hide-bound bureaucrat 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

 

[Jerry Avins]

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

 

[[email protected]]

Quite well...

Got numbers?

Nick

 

[William P.N. Smith]

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.

 

[Will]

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?

 

[Jerry Avins]

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.

And the heat shorts the neighboring cells. It works both ways.

Jerry

 

[Jerry Avins]

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?

The shorting process is accelerated by heat. If you notice the external
temperature of a battery rising spontaneously, you may have less than
five minutes to cut it loose, probably less than half an hour.

Jerry

 

[William P.N. Smith]

And the heat shorts the neighboring cells. It works both ways.

Right, it's a thermal runaway. Hard to predict, hard to control, easy
to avoid.

 

[budgie]

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.

and the subsequent damage by a none-too-bright charging system.

 

[budgie]

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?

Sometimes - but certainly not always - you can detect slight bulging of the case
which pre-empts failure in SLA's. Apart from that, as others have pointed out,
failure can be rather sudden and without warning, especially if it results from
internal shorting.

You MAY be able to pick other types of deterioration by ESR measurements, but I
have never bothered. Also sometimes timing a regular test run to cutoff will
give early warning. But neither reliably warns of an impending shorted cell.

 

[budgie]

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.

and then the manufacturers decided to bury the inter-cell links where you
couldn't access them without drilling into the wet chambers.

 

[Roy L. Fuchs]

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.

Lead acid gel cells exhibit heat when charged. It is a simple fact.
Period.

 

[Peter Dettmann]

You also have probelms keeping your posts just to appropriate news
groups. SPAM is what is is.

Peter Dettmann

 

[Roy L. Fuchs]

You also have probelms keeping your posts just to appropriate news
groups. SPAM is what is is.

Peter Dettmann

Yet your retarded ass had to quote and repost the entire chunk of
crap again.

You TOFUd it too.

Looks like you need to learn a few things about Usenet as well.

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

 

[[email protected]]

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.

I doubt that.

Nick

 

[William P.N. Smith]

You also have probelms keeping your posts just to appropriate news
groups. SPAM is what is is.

Oh, I dunno, I invited him over to alt.energy.homepower from the
battery newsgroup, as there are a lot more people here with battery
experience. He might have ranged a bit wider than I would have, but
it's certainly marginally on-topic for these groups.

And SPAM is unsolicited commercial advertising, which I don't see any
of here. If you don't like the thread, click that little "ignore
thread" button underneath where it says "Tools".

 

[Eric Sears]

(snip)

???? a 3000VA inverter is going to want 250A @12V input, assuming 100%
efficiency. There IS a reason why higher input voltages are used as the output
rating climbs. Even my 1000VA unit runs a 60V string of 5*12V.

I absolutely agree.
However, since the originator of this thread wanted something that was
easier to "fail-proof" I thought that less cells might be better (even
if larger amperage capacity).
My 350 watt UPS has a single 12v/6ah battery - which I guess means
that at full power it might draw 30 amps (not for long!). So maybe I
should have said about 50 ah for 3kw if scaled correctly.

But you are correct about input power. I suppose that most UPS's have
the "inverter" part running in sync with the grid power all the time,
and the battery only gets called on when the grid fails.

Perhaps a standard 48v inverter would be better, but then there is the
problem of "all those cells".

I guess in the end, as others have said, the best system is a regular
maintenance schedule of replacing batteries at a set time period.
If the regular batteries in the UPS were re-sited OUTSIDE the box, it
might be possible to a) prevent the heat from one battery affecting
the adjacent ones and b) monitor the individual battery voltages more
easily.

Thanks for your comments budgie.

Eric Sears.

 

[JoeSP]

I doubt that.

Nick

LOL

 

[JoeSP]

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?

Our organization has opted for the simplest solution I can think of. Two
UPS's, one backing up the line, and the other backing up the first. They are
made of 10 gel cells each, inverted to AC without the need of a step-up
transformer. For long power failures, when one cuts out, the other one
takes over, to give us well over 4 hours of backup power. It also gives us
the redundancy of having two systems that won't fail at the same time. A
warning beep alerts us when the battery is no longer taking a proper charge
and needs to be replaced.