UPS batteries

[D Yuniskis]

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply. And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer). But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?

 

[John Robertson]

D Yuniskis wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply. And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer). But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?

Here is where I visit when I have battery questions:

http://batteryuniversity.com/

Float voltage is critical for long storage battery life - +/- 0.01V!

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[William R. Walsh]

Hi!

We rarely have outages here.  So, there is no real
draw on the batteries in our UPS's.  So, they should just
be on float charges.

I rarely have power outages here, and my most recent UPS battery
change involved a unit that did nothing more than "buffer" a phone
system until a generator would come on. Its battery lasted 10 years
(1998-2008). The UPS in question is an APC Back-UPS 600.

I attribute part of that long lifetime to the fact that the battery
could have degraded to where it had almost no runtime left--but that
would have been fine as the generator started and stabilized within a
few seconds.

Can anyone with firsthand knowledge shed some light on
this?

I can't say that I have firsthand knowledge. (Meaning: I've never
designed or built a UPS circuit from scratch...) However, the trouble
is likely to come from the float charging. I'm of the impression that
at least some UPS units have an awfully "hot" float charge and it
probably leads to the battery being overcharged. I've seen some Tripp-
Lite UPS units that would slowly drive the water out of their
batteries if left float charging all the time.

I also think there are some that don't put enough of a float charge on
a battery to truly keep it up. I have an older APC Smart-UPS 1000 that
demonstrates this behavior--if the power hasn't been out in a while,
the battery will drop more quickly than it does when the unit has had
only a short time (a few days) between the completion of a battery
charge after use and a subsequent power outage.

You also have to consider that some UPS designs depend upon their
battery and inverter to deal with *every* little power line anomaly.
This too will shorten the battery's useful life. This seems to be true
of the inexpensive APC "plugstrip" UPS units that many people have.

Better designs have methods by which to stabilize, boost or trim the
power coming out of them without having to use the battery and
inverter.

William

 

[Van Chocstraw]

D Yuniskis wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply. And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer). But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?

I know what you mean. By the time you need the UPS, the batteries won't
carry a load. I found out that the chargers 'cook' the batteries.
I hooked up 2 motorcycle batteries to replace my dead ones. You need 2
to make 24 volts in series. The Belkin UPS boiled the water out of them
in 2 weeks. They are poorly designed.

 

[who where]

On Mon, 07 Dec 2009 14:09:42 -0700, D Yuniskis
<not.going.to.be@seen.com> wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply.

That's not what kills most UPS batteries.

And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer).

That, but also an unreasonably high float voltage, is what kills them.
We've seen literally dozens of UPS' from assorted manufacturers with
failed batteries - baked dry, swollen, cracked cases. On fitting new
batteries and checking the charger behaviour, we note that the
recovery charge rate is definitely "too aggressive" (motive onvious)
and the eventual float charge voltage was definitely destined to kill
the cells within a year or so.

The only time we were happy that the cells were within the
manufacturer approved envelope was ... on DISCHARGE.

But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?

 

[Sylvia Else]

who where wrote:

On Mon, 07 Dec 2009 14:09:42 -0700, D Yuniskis
not.going.to.be@seen.com> wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply.

That's not what kills most UPS batteries.

And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer).

That, but also an unreasonably high float voltage, is what kills them.
We've seen literally dozens of UPS' from assorted manufacturers with
failed batteries - baked dry, swollen, cracked cases. On fitting new
batteries and checking the charger behaviour, we note that the
recovery charge rate is definitely "too aggressive" (motive onvious)
and the eventual float charge voltage was definitely destined to kill
the cells within a year or so.

The only time we were happy that the cells were within the
manufacturer approved envelope was ... on DISCHARGE.

But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?

Both my old and my new SOLA UPS use a float voltage of 13.5 volts (near
enough), which is at the low end of the battery manufacturer's
recommendation (13.5 to 13.8). I get about three years out of batteries
in the old UPS. Too soon to say about the new one.

Once a month, the UPS switches to battery power for a minute, to test
the batteries. Given the current drawn, I have to wonder whether the
self test function itself tends to limit the life of the batteries.

Tests on the rejected batteries suggests that they still have 2/3 of
their nominal capacity - but maybe they can't deliver the current required.

Sylvia.

 

[Meat Plow]

On Mon, 07 Dec 2009 14:09:42 -0700, D Yuniskis
<not.going.to.be@seen.com>wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

I own two APC 1000va units purchased around 2002. Both function
perfect and do self tests regularly. Both have 'replace battery'
indication if they fail the self test. Neither are tethered to a
computer. Also own a 350va APC unit that provides power for my
modem and network storage device. It was purchased around 2004
and last time I tested it in Oct it ran for an hour unplugged.

I've seen plenty of APC units fail prematurely though so I really
don't understand the reasons why some do and some don't. And I've
owned other brands besides APC but they were not long-lived.

 

[Sylvia Else]

Meat Plow wrote:

It was purchased around 2004
and last time I tested it in Oct it ran for an hour unplugged.

That's a long time for a UPS, and suggest's it's not heavily loaded. The
self test would be similarly undemanding.

Sylvia.

 

[Meat Plow]

On Tue, 08 Dec 2009 23:32:19 +1100, Sylvia Else
<sylvia@not.at.this.address>wrote:

Meat Plow wrote:
It was purchased around 2004
and last time I tested it in Oct it ran for an hour unplugged.

That's a long time for a UPS, and suggest's it's not heavily loaded. The
self test would be similarly undemanding.

The 350va powers a cable modem, two USB hard drives and a Linksys
network storage server 24/7/365.

The self test on the two 1000va units simulate a power failure
allowing them to run off battery power for 10 seconds or so. Enough
time for the unit to evaluate the state of the batteries according to
how it was designed. One 1000va unit provides power for a SA Explorer
HDTV cable DVR and a Panasonic 51" rear projector TV. The other
powers a 3 yr old desktop PC and 22" monitor and a 32" LCD HDTV.

I don't think you understand the principals of demand or load well
enough.

 

[PeterD]

On Mon, 07 Dec 2009 14:09:42 -0700, D Yuniskis
<not.going.to.be@seen.com> wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

Define "most".

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

A quality UPS (not one of those cheap Chinese POS units) will
regularly exercise the batteries, running discharge/charge cycles and
measuring the results. Then the UPS will tell you the condition of the
batteries.

Yet, the batteries seem to wear out far too frequently, IMO.

So you keep a mystery what brand and model UPS you are using...

 

[Thomas Tornblom]

Meat Plow <meat@petitmorte.net> writes:

On Tue, 08 Dec 2009 23:32:19 +1100, Sylvia Else
sylvia@not.at.this.address>wrote:

Meat Plow wrote:
It was purchased around 2004
and last time I tested it in Oct it ran for an hour unplugged.

That's a long time for a UPS, and suggest's it's not heavily loaded. The
self test would be similarly undemanding.


The 350va powers a cable modem, two USB hard drives and a Linksys
network storage server 24/7/365.

The self test on the two 1000va units simulate a power failure
allowing them to run off battery power for 10 seconds or so. Enough
time for the unit to evaluate the state of the batteries according to
how it was designed. One 1000va unit provides power for a SA Explorer
HDTV cable DVR and a Panasonic 51" rear projector TV. The other
powers a 3 yr old desktop PC and 22" monitor and a 32" LCD HDTV.

I don't think you understand the principals of demand or load well
enough.

My APC SmartUPS 700 successfully ran selftests up until one of the
batteries failed and everything it supplied went down. :-(

It runs with a maximum load of 30%.

I have been contemplating using two full size 60Ah car batteries
externally instead of the small 7Ah internals.

 

[Bennett Price]

Don't automatically assume that doubling the batteries will extend the
run time. I was very surprised.

I've a 9 year old APC Smart-700 UPS. I tried at one point doubling up
on the batteries to extend run time. It performed as expected without
the powerchute software running - more than doubling the run time.

With powerchute, it performed as if the extra batteries were not there;
the run-time calibration 'couldn't see' the extra batteries, perhaps
because the EPROM 'knows' that no external batteries were installed.
I'd thought the hw/sw would look at the battery voltage (only) and use
that value to decide when to shut down; didn't happen.

You may get different results - different models, mfrs. firmware, etc.

 

[William R. Walsh]

Hi!

I own two APC 1000va units purchased around 2002. Both
function perfect and do self tests regularly. Both have 'replace
battery' indication if they fail the self test.

Don't expect that it will work. If any of my APC UPS units (about 12)
are anything to by, the only way you'll know the battery is dead is
when it fails to support the load. Most of these are not cheap units,
either--they are SmartUPS units that have a true sinewave inverter. So
far, only one has ever illuminated the "battery fault" indicator as a
result of a self test.

Even if they fail to support the load entirely, this is not enough to
trip the fault indicator.

I've seen plenty of APC units fail prematurely though so I really
don't understand the reasons why some do and some don't.

The ones I've seen the most failures out of are the ones that were
made in China. Every one of them failed in the same way--I came in and
found they were dead to the world. No fuses or breakers had blown, and
the batteries were good. Out of four units, three have failed in this
way. The fourth works but does not really charge its batteries
properly.

None of my APC units marked as being made in the US or India have
failed. Some of them are over ten years old (having had their
batteries replaced, of course).

And I've owned other brands besides APC but they were
not long-lived.

I've had good results with APC and Tripp Lite units. Everything else
(Belkin, Cyber Power) seems to have a poor lifetime
and...interesting...build quality. I have a big stack of CyberPower
units and they all look to have failed in the same way--something
inside them simply got too hot and gave up the ghost. And every one
has had a bad battery. Never seen any Belkin units, but I've heard bad
things about them...

Buying a UPS that is larger than you need will also improve the
lifetime of the unit and its batteries. The ratings provided by the
manufacturers are VERY optimistic and only result in a few minutes of
operation.

William

 

[D Yuniskis]

Hi William,

(and "All" -- I'll try to address all of the posts I have
seen here instead of with individual replies)

William R. Walsh wrote:

I rarely have power outages here, and my most recent UPS battery
change involved a unit that did nothing more than "buffer" a phone
system until a generator would come on. Its battery lasted 10 years
(1998-2008). The UPS in question is an APC Back-UPS 600.

IME, when the batteries are toast, you won't get *any* up-time
from the UPS. Power goes... and so does the UPS! :-/

I attribute part of that long lifetime to the fact that the battery
could have degraded to where it had almost no runtime left--but that
would have been fine as the generator started and stabilized within a
few seconds.

Can anyone with firsthand knowledge shed some light on
this?

I can't say that I have firsthand knowledge. (Meaning: I've never
designed or built a UPS circuit from scratch...) However, the trouble
is likely to come from the float charging. I'm of the impression that

Agreed.

at least some UPS units have an awfully "hot" float charge and it
probably leads to the battery being overcharged. I've seen some Tripp-
Lite UPS units that would slowly drive the water out of their
batteries if left float charging all the time.

I've seen lots of UPS's discarded because they have killed
their battery packs. Bulging battery cases, cracks, etc.

I also think there are some that don't put enough of a float charge on
a battery to truly keep it up. I have an older APC Smart-UPS 1000 that
demonstrates this behavior--if the power hasn't been out in a while,
the battery will drop more quickly than it does when the unit has had
only a short time (a few days) between the completion of a battery
charge after use and a subsequent power outage.

You also have to consider that some UPS designs depend upon their
battery and inverter to deal with *every* little power line anomaly.
This too will shorten the battery's useful life. This seems to be true
of the inexpensive APC "plugstrip" UPS units that many people have.

Some UPS's actually power the load continuously and are
recharging the battery from the AC line (like telco's operate).
I would think this would be more stressful on the switching
power supply than the battery (as, essentially, the same current
is flowing into the battery as out)

Better designs have methods by which to stabilize, boost or trim the
power coming out of them without having to use the battery and
inverter.

I (currently) have:
1x Back-UPS Pro 500
2x Back-UPS ES 550
2x Back-UPS XS 1000
1x Back-UPS RS 1500
1x MX 3000
(all APCC)

I discarded a Belkin unit that appeared to be a repackaged
Pro 500 (actually had the nice feature of using a removable
power cord!)

I've also previously discarded a Back UPS 600 (?) as it used
a different physical size battery that was hard to come by
(since it didn't offer any feature that I didn't have on other
UPS's -- and, also had two pigtail power outlets on the
rear which always seemed like a kludge).

I discarded a large HP "UPS 1000" which was a decent box (I
think Astec internals) but totally unsupported. IIRC, it
ran off 48V and had another 48V external battery pack.

I managed to blow up another larger UPS (3KVA... the size of
a dishwasher) by forgetting that power was still available
from the battery pack even though the AC mains were
disconnected... shorting a 120V battery into damn near anything
destroys the "anything"! :< )

All of my UPS's are connected to PC's or servers. So, all feed
reactive loads. Most are oversized for the loads they power.
Occasionally, I will run an extension cord from one of them to
power a CF light in another room if we have an outage at night.
(a "100 equivalent watt" CF runs for a LONG TIME on a small UPS!)

All of the APCC devices have "replace battery" indicators.
All of them do a loaded test on power up (for about 2-3 seconds).
I am not sure if they periodically run other tests as it is
hard to hear the characteristic "buzz" that accompanies the test
when a server is running (fan noise). I think all are tied in
to their respective computer/server (typically USB or EIA232)
though that should just help the machine shut down before power
is pulled.

I think all of the APCC designs use low voltage primaries. E.g.,
12 or 24V. I don't know if the battery abuse is consequential
to this (perhaps the charging circuits on the UPS's that I've
had that utilized 48V or 120V primaries were better designed
of necessity?)

I've taken to powering the UPS's off when their loads are not
in use. I.e., they can (over?)charge their batteries only while
I am using their loads. Thereafter, they act like power strips
and let me shut down all of the loads. This is intended to
see if the problem I -- and associates -- have been seeing is
related to an aggressive float. (it also has the advantage of
silencing the silly alarms that signal in the event of a power
outage -- if the UPS is on but its loads are NOT, then I really
don't want to be bothered by a chorus of half a dozen little
"chirpers"!)

I don't think it prudent to use regular lead acid batteries
("car batteries") in these applications unless the batteries
themselves could be located in a ventilated area -- I'd be
wary of outgassing. I had thought of replacing the gelled
electrolyte batteries in the UPS that I blew up with car
batteries (this would have required *10* such batteries)
and locating the UPS in the garage with the batteries on
the outside of the building for this very reason. Then,
starving the electrolyte in those batteries to improve
longevity.

In the short term, I see no other remedy for "fixing" the
battery mongers... :<

 

[Van Chocstraw]

D Yuniskis wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply. And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer). But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?

Better off to make your own. All you need is a good car battery, trickle
charger, RV inverter and a couple relays.

 

[Sylvia Else]

Meat Plow wrote:

I don't think you understand the principals of demand or load well
enough.

<blink> Where did you get that from?

A normal 1000VA unit would not usually have sufficient storage to
provide anything approaching 1000VA for an hour. So unless it's a
specially high capacity unit, the fact that it can supply its actual
load for an hour suggests that that load is nothing like 1000VA.

Sylvia.

 

[Sylvia Else]

Thomas Tornblom wrote:

Meat Plow <meat@petitmorte.net> writes:

On Tue, 08 Dec 2009 23:32:19 +1100, Sylvia Else
sylvia@not.at.this.address>wrote:

Meat Plow wrote:
It was purchased around 2004
and last time I tested it in Oct it ran for an hour unplugged.
That's a long time for a UPS, and suggest's it's not heavily loaded. The
self test would be similarly undemanding.

The 350va powers a cable modem, two USB hard drives and a Linksys
network storage server 24/7/365.

The self test on the two 1000va units simulate a power failure
allowing them to run off battery power for 10 seconds or so. Enough
time for the unit to evaluate the state of the batteries according to
how it was designed. One 1000va unit provides power for a SA Explorer
HDTV cable DVR and a Panasonic 51" rear projector TV. The other
powers a 3 yr old desktop PC and 22" monitor and a 32" LCD HDTV.

I don't think you understand the principals of demand or load well
enough.

My APC SmartUPS 700 successfully ran selftests up until one of the
batteries failed and everything it supplied went down. :-(

That doesn't sound a very sensible design - the expression "next to
useless" comes to mind, since it pretty much guarantees the very failure
it's designed to protect against. My SOLA UPS certainly didn't do that
on any of the times when it decided that the batteries were no longer up
to the task.

Sylvia.

 

[Michael A. Terrell]

Thomas Tornblom wrote:

Meat Plow <meat@petitmorte.net> writes:

On Tue, 08 Dec 2009 23:32:19 +1100, Sylvia Else
sylvia@not.at.this.address>wrote:

Meat Plow wrote:
It was purchased around 2004
and last time I tested it in Oct it ran for an hour unplugged.

That's a long time for a UPS, and suggest's it's not heavily loaded. The
self test would be similarly undemanding.


The 350va powers a cable modem, two USB hard drives and a Linksys
network storage server 24/7/365.

The self test on the two 1000va units simulate a power failure
allowing them to run off battery power for 10 seconds or so. Enough
time for the unit to evaluate the state of the batteries according to
how it was designed. One 1000va unit provides power for a SA Explorer
HDTV cable DVR and a Panasonic 51" rear projector TV. The other
powers a 3 yr old desktop PC and 22" monitor and a 32" LCD HDTV.

I don't think you understand the principals of demand or load well
enough.

My APC SmartUPS 700 successfully ran selftests up until one of the
batteries failed and everything it supplied went down. :-(

It runs with a maximum load of 30%.

I have been contemplating using two full size 60Ah car batteries
externally instead of the small 7Ah internals.

Make sure you keep a couple fire extinguishers handy.


--
Offworld checks no longer accepted!

 

[who where]

On Tue, 08 Dec 2009 13:14:30 +1100, Sylvia Else
<sylvia@not.at.this.address> wrote:

who where wrote:
On Mon, 07 Dec 2009 14:09:42 -0700, D Yuniskis
not.going.to.be@seen.com> wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply.

That's not what kills most UPS batteries.

And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer).

That, but also an unreasonably high float voltage, is what kills them.
We've seen literally dozens of UPS' from assorted manufacturers with
failed batteries - baked dry, swollen, cracked cases. On fitting new
batteries and checking the charger behaviour, we note that the
recovery charge rate is definitely "too aggressive" (motive onvious)
and the eventual float charge voltage was definitely destined to kill
the cells within a year or so.

The only time we were happy that the cells were within the
manufacturer approved envelope was ... on DISCHARGE.

But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?


Both my old and my new SOLA UPS use a float voltage of 13.5 volts (near
enough), which is at the low end of the battery manufacturer's
recommendation (13.5 to 13.8). I get about three years out of batteries
in the old UPS. Too soon to say about the new one.

That takes care of one of the killer parameters - float voltage. But
at what rate do they recharge after a serious discharge?

Once a month, the UPS switches to battery power for a minute, to test
the batteries. Given the current drawn, I have to wonder whether the
self test function itself tends to limit the life of the batteries.

The battery current to provide full UPS output is generally pushing
the envelope. But vecause it is typically for ten minutes or less, it
is generally not that deleterious IMOE.

Tests on the rejected batteries suggests that they still have 2/3 of
their nominal capacity - but maybe they can't deliver the current required.

Capacity, yes. But internal resistance will be too high to allow any
decent discharge current..

 

[Sylvia Else]

who where wrote:

On Tue, 08 Dec 2009 13:14:30 +1100, Sylvia Else
sylvia@not.at.this.address> wrote:

who where wrote:
On Mon, 07 Dec 2009 14:09:42 -0700, D Yuniskis
not.going.to.be@seen.com> wrote:

Hi,

I don't have anything other than "gut feel" to resort to
as evidence but it sure *seems* like most UPS designs
EAT batteries!

We rarely have outages here. So, there is no real
draw on the batteries in our UPS's. So, they should just
be on float charges.

Yet, the batteries seem to wear out far too frequently, IMO.

I could possibly understand regular outages cycling the
batteries too deeply.
That's not what kills most UPS batteries.

And, chargers too aggressively
replenishing them (after all, a UPS that quits because its
battery wasn't fully recharged earns a bad reputation for
its manufacturer).
That, but also an unreasonably high float voltage, is what kills them.
We've seen literally dozens of UPS' from assorted manufacturers with
failed batteries - baked dry, swollen, cracked cases. On fitting new
batteries and checking the charger behaviour, we note that the
recovery charge rate is definitely "too aggressive" (motive onvious)
and the eventual float charge voltage was definitely destined to kill
the cells within a year or so.

The only time we were happy that the cells were within the
manufacturer approved envelope was ... on DISCHARGE.

But, I can't see how even periodic
battery tests (performed by the UPS itself) could be the
problem -- unless there is something wrong with the
approach being used?

Can anyone with firsthand knowledge shed some light on this?
I.e., what *is* the UPS doing to/with the battery when it
is not being used to supply the load?
Both my old and my new SOLA UPS use a float voltage of 13.5 volts (near
enough), which is at the low end of the battery manufacturer's
recommendation (13.5 to 13.8). I get about three years out of batteries
in the old UPS. Too soon to say about the new one.

That takes care of one of the killer parameters - float voltage. But
at what rate do they recharge after a serious discharge?

I haven't checked that. My AVO meter apparently has a significant
voltage drop on its current range which messes up the result

Sylvia.