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measuring 12V 12Ah Lead-Acid battery

A

aurgathor

Jan 1, 1970
0
I opened up my UPS (APC Pack-UPS Pro 650) that
occasionally beeps on me and flashes a battery failed light.

Upon first measurement, I measured 13.78V (holy smoke!!)
across the battery. (AC was disconnected for a few minutes
before). Figured that's the surface charge, so I hooked up
a 12V domelight from my Cutlass until it dropped to about 12.7V
in a few minutes. Disconnected light, and now it's back to 13.08V.

So, how do I measure the capacity of the battery, or how do
I determine whether it's good, OK, marginal, or bad?
I have a couple DMMs, and got a sealed beam headlight I
could put on as a more meaningful (though slightly non-linear)
load.

The battery doesn't appear bad to me, though I have a feeling
that it may be a bit overcharged.

TIA,
aur
 
K

Ken

Jan 1, 1970
0
I opened up my UPS (APC Pack-UPS Pro 650) that
occasionally beeps on me and flashes a battery failed light.

Upon first measurement, I measured 13.78V (holy smoke!!)
across the battery.

That's normal voltage.

(AC was disconnected for a few minutes before).
Figured that's the surface charge, so I hooked up
a 12V domelight from my Cutlass until it dropped to about 12.7V
in a few minutes. Disconnected light, and now it's back to 13.08V.

So, how do I measure the capacity of the battery,
or how do I determine whether it's good, OK, marginal, or bad?
I have a couple DMMs, and got a sealed beam headlight I
could put on as a more meaningful (though slightly non-linear)
load.

The battery doesn't appear bad to me, though I have a feeling
that it may be a bit overcharged.

The charging voltage is OK. 13.60V - 13.80V is normal.

Your problem can be bad connection on the battery terminals.
You have to tightening the terminal contacts.
The current can be over 50A from the battery and you need a very
good contact on the battery terminals to prevent voltage drop!
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that aurgathor <[email protected]>
So, how do I measure the capacity of the battery, or how do I determine
whether it's good, OK, marginal, or bad? I have a couple DMMs, and got a
sealed beam headlight I could put on as a more meaningful (though
slightly non-linear) load.

Well, you've proved for yourself that open-circuit voltage is no use as
a measure of capacity.

Use the headlight to time how long it takes to discharge the battery to
10 V on load. Compare headlight watts/12 (= nominal current) x time in
hours with the ampere-hour capacity marked on the battery. If the two
figure are in the same ball-park (you won't get better accuracy without
a far more complicated test), the battery is OK. For example, if it runs
a 60 W light for 2 hours down to 10 V, you have 5 A x 2 hours = 10
ampere-hours. For a 600 W UPS, that's a good enough battery.
The battery doesn't appear bad to me, though I have a feeling that it
may be a bit overcharged.

Unlikely, unless your UPS is faulty. Make sure that the battery
connections are clean and tight.

Sometimes, an APC UPS will give a false 'battery low' indication if you
try to start it with a load connected. Disconnect all loads and then
start the UPS.
 
J

John Doe

Jan 1, 1970
0
Ken said:
Your problem can be bad connection on the battery terminals.
You have to tightening the terminal contacts.
The current can be over 50A from the battery and you need a very
good contact on the battery terminals to prevent voltage drop!

Hmm, this is definitely a possibility, though I'm not exactly sure
how do I tighten up the contacts because the battery is equipped
with F2 faston terminals, and F2's plus F1's are used pretty much
everywhere on the PCB. I assume I can replace the two main
connectors on the PCB with something better if the contacts are
the culprit, though I'll probably try contact clean, or burnishing first.

BTW, to much of my surprise I found the battery's PDF:
http://www.csb-battery.com/Top/pdf/gp_12120.pdf
so I'll do a load test on it tomorow; umm, err, later today. ;-)
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
aurgathor said:
I opened up my UPS (APC Pack-UPS Pro 650) that
occasionally beeps on me and flashes a battery failed light.

Upon first measurement, I measured 13.78V (holy smoke!!)
across the battery. (AC was disconnected for a few minutes
before). Figured that's the surface charge, so I hooked up
a 12V domelight from my Cutlass until it dropped to about 12.7V
in a few minutes. Disconnected light, and now it's back to 13.08V.

So, how do I measure the capacity of the battery, or how do
I determine whether it's good, OK, marginal, or bad?
I have a couple DMMs, and got a sealed beam headlight I
could put on as a more meaningful (though slightly non-linear)
load.

The battery doesn't appear bad to me, though I have a feeling
that it may be a bit overcharged.

TIA,
aur

forget about measuring the capacity, and just connect it up to your
load, and unplug the power cord aqnd see how long it holds the load.
The rule of thumb is that if the battery is 5 years old or more, it
should be replaced. This time length could be a lot less if the battery
has had to supply heavy load current often. In other words, the battery
gets 'used up' when it is deeply discharged a lot. If you depend on
this UPS for backing up your important computer, then don't mess around.
Get a new battery.
 
J

Jerry G.

Jan 1, 1970
0
The battery is probably not loading the charging section of the UPS, and it
is probably not passing the load test that the UPS does. You must load the
battery at about 2 times its amp rating, and determine the time the load
should run, in order to properly test the battery. Your car headlamp is
nowhere near the proper load test required.

Generally speaking, the battery should be replaced about every 3 years in a
UPS. Sometimes I have seen them go for about 5 years, but this is rare. We
replace them every 3 years, because it is cheaper than waiting for a total
failure, and then having a more expensive data or computer loss.

--

Jerry G.
======


I opened up my UPS (APC Pack-UPS Pro 650) that
occasionally beeps on me and flashes a battery failed light.

Upon first measurement, I measured 13.78V (holy smoke!!)
across the battery. (AC was disconnected for a few minutes
before). Figured that's the surface charge, so I hooked up
a 12V domelight from my Cutlass until it dropped to about 12.7V
in a few minutes. Disconnected light, and now it's back to 13.08V.

So, how do I measure the capacity of the battery, or how do
I determine whether it's good, OK, marginal, or bad?
I have a couple DMMs, and got a sealed beam headlight I
could put on as a more meaningful (though slightly non-linear)
load.

The battery doesn't appear bad to me, though I have a feeling
that it may be a bit overcharged.

TIA,
aur
 
M

mike

Jan 1, 1970
0
aurgathor said:
I opened up my UPS (APC Pack-UPS Pro 650) that
occasionally beeps on me and flashes a battery failed light.

Upon first measurement, I measured 13.78V (holy smoke!!)
across the battery. (AC was disconnected for a few minutes
before). Figured that's the surface charge, so I hooked up
a 12V domelight from my Cutlass until it dropped to about 12.7V
in a few minutes. Disconnected light, and now it's back to 13.08V.

So, how do I measure the capacity of the battery, or how do
I determine whether it's good, OK, marginal, or bad?
I have a couple DMMs, and got a sealed beam headlight I
could put on as a more meaningful (though slightly non-linear)
load.

The battery doesn't appear bad to me, though I have a feeling
that it may be a bit overcharged.

TIA,
aur

Most of my failures have been due to increased series resistance.
Just replaced a set yesterday. 6V cells easured almost 7V open circuit
and quickly dropped to 4.3V under load.
Stick on enough light bulbs to match your load and measure the battery
volts.
mike
--
Return address is VALID.
500MHz Tek DSOscilloscope TDS540 $2200
http://nm7u.tripod.com/homepage/te.html
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/
 
A

aurgathor

Jan 1, 1970
0
Thanks for the replies.
Well, you've proved for yourself that open-circuit voltage
is no use as a measure of capacity.

Yes, I do know very well that the open circuit measurement
may not be very meaningful, that's why I'm asking for help.
I guess I'll just put up some load and measure how long it takes
run it down to 10Vas you said, and calculate capacity from that.
Although I think there exists some equation or formula which
allows capacity can be computed from a few measurement points
taken in time under some reasonable load.
Sometimes, an APC UPS will give a false 'battery low'
indication if you try to start it with a load connected.
Disconnect all loads and thenstart the UPS

While some bad battery warning happeneed when I tried to start
my PC on a non-fully charged UPS, the irritating ones seem to
happen randomly after some time (usual;ly weeks) of running.
Turning everything off, then restarting the UPS first usually fixes
the problem.
forget about measuring the capacity, and just connect it
up to your load

This is simple, but it also puts in the conversion losses.
If you depend on this UPS for backing up your important
computer, then don't mess around. Get a new battery.

Nothing is very important that really require UPS protection,
but I have quite a few brownouts and dropouts usually lasting
for a few seconds, and they can be very irritating.
it is probably not passing the load test that the UPS does.

That's very possible, but the thing I don't understand that
it can run for a long time just fine, then fail randomly. The
first time it happened was about a year ago, afterwards I
lessened the load on the UPS, but it happened again after
a while. I'd say the frequency is about 1 warning every other
month. If I had daily or constant warnings, yes, I'd say the
battery is probably no good.
If you have $300 to spend, get this great battery checker.

Very nice, but I don't think I can justify it right now. :-(
Most of my failures have been due to increased series
resistance. Just replaced a set yesterday. 6V cells
measured almost 7V open circuit and quickly dropped
to 4.3V under load. Stick on enough light bulbs to match
your load and measure the battery

Will do that, but I need to get a 0.1 ohm or so resistor to
measure current first.

aur
 
M

mike

Jan 1, 1970
0
aurgathor said:
Thanks for the replies.




Yes, I do know very well that the open circuit measurement
may not be very meaningful, that's why I'm asking for help.
I guess I'll just put up some load and measure how long it takes
run it down to 10Vas you said, and calculate capacity from that.
Although I think there exists some equation or formula which
allows capacity can be computed from a few measurement points
taken in time under some reasonable load.




While some bad battery warning happeneed when I tried to start
my PC on a non-fully charged UPS, the irritating ones seem to
happen randomly after some time (usual;ly weeks) of running.
Turning everything off, then restarting the UPS first usually fixes
the problem.




This is simple, but it also puts in the conversion losses.




Nothing is very important that really require UPS protection,
but I have quite a few brownouts and dropouts usually lasting
for a few seconds, and they can be very irritating.




That's very possible, but the thing I don't understand that
it can run for a long time just fine, then fail randomly. The
first time it happened was about a year ago, afterwards I
lessened the load on the UPS, but it happened again after
a while. I'd say the frequency is about 1 warning every other
month. If I had daily or constant warnings, yes, I'd say the
battery is probably no good.




Very nice, but I don't think I can justify it right now. :-(




Will do that, but I need to get a 0.1 ohm or so resistor to
measure current first.

aur

Measuring with resistors is problematic. 0.1ohm and 15amps is
1.5V. that's a lot in a 12V system. Clamp-on DC currrent probe
is your best bet. But you don't really care about the 12V current.
Load the AC side with the watts you need. The 12V current is whatever the
current is. You can't change it anyway. Just measure the voltage
for an INDICATION of how sad the batteries are. But even that is moot.
It runs for X minutes before shutting off. If you need more, change
the batteries. If you don't need more, it ain't broke.

Batteries are often rated at a 20 hour discharge rate. You can't expect
to get half the time at twice the current. And you sure can't expect
1/40 the time at the typical 40x current. Search the lead-acid battery
vendors. You'll probably find typical curves.
Consumer grade UPS systems SERIOUSLY
abuse batteries. They draw too much current when on and they charge too
much when off. I'd even bet that the cheapo batteries they use in
consumer systems don't even meet their spec at 20 hours. Most of us are
WAY more concerned about saving an extra buck than whether it runs 6 or
6.2 minutes.
mike

--
Return address is VALID.
500MHz Tek DSOscilloscope TDS540 $2200
http://nm7u.tripod.com/homepage/te.html
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/
 
A

aurgathor

Jan 1, 1970
0
Measuring with resistors is problematic. 0.1ohm and 15amps is
1.5V. that's a lot in a 12V system. Clamp-on DC currrent probe
is your best bet.

You're probably right, but I could always get by without one. ;-)
How much do they normally go for?
Load the AC side with the watts you need. The 12V current is whatever the
current is. You can't change it anyway. Just measure the voltage
for an INDICATION of how sad the batteries are. But even that is moot.
It runs for X minutes before shutting off. If you need more, change
the batteries. If you don't need more, it ain't broke.

The problem is not running time -- it's the occasional beeping and
battery bad light with seemingly no good reason. (the UPS is in
my bedroom) If the battery is indeed bad, I will replace it, but I
want to make sure it's really bad, and it's not something else that
causing the problem, with bad contacts being another possible cause.
 
J

Jean Castonguay

Jan 1, 1970
0
May I suggest the original poster to take the battery to his friendly
service station. They have a battery tester that can apply a lot of
up to perharps 400 or 500 A.
 
A

aurgathor

Jan 1, 1970
0
Well, it could be the battery after all. I hooked
up a headlight that started out at 2.6A, and
1 hour 20 mins later the battery reads only 9.50V
(loaded) while the current draw is down to 2.3A.
Looking at the terminal voltage/discharge time
graph, this battery appears to be around 50%.

PS: it's now down to 8.9V in just a few minutes,
so I guess I'm at the knee, and it's time to stop
this before I run it down completely.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Jerry G. said:
The battery is probably not loading the charging section of the UPS, and it
is probably not passing the load test that the UPS does. You must load the
battery at about 2 times its amp rating, and determine the time the load
should run, in order to properly test the battery. Your car headlamp is
nowhere near the proper load test required.

Generally speaking, the battery should be replaced about every 3 years in a
UPS. Sometimes I have seen them go for about 5 years, but this is rare. We
replace them every 3 years, because it is cheaper than waiting for a total
failure, and then having a more expensive data or computer loss.

Yeah, my boss was complaining because we had to spend several thousand
on UPSes to replace those over 5 years old. And it took almost two
years, so some of then were more like 7 years. And now we found that
the batteries on the 48VDC rectifier for the PBX say that they were
installed in '95, so they're over 9 years old. Those are gonna cost
some big money to replace.
 
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