APC Smart-UPS ... battery float voltage adjustment?
 

Does anyone know how to adjust the voltage at which an APC Smart-UPS floats
its batteries? Their factory default at room temperature seems to be about
2.33V/cell, which exceeds the manufacturer-recommended voltages for every
sealed-lead acid battery I've looked up (equivalent to 14.0V on a 12V string).

We've had to replace batteries these UPSes every 2-3 years, on average,
probably as a result of electrolyte loss from the high charging voltage.

On smaller APCs (Back-UPS line), it's easy enough to tweak a trim pot inside
and turn down the charging voltage. This decreases the runtime slightly, but
does halp the batteries last longer. But Smart-UPSes have no such adjustment
pot... their charging regime seems to be under the microprocessor's control.

Can this be controlled from an attached PC through the serial interface?
APC's tools seem to offer no such option, but I've heard rumors about an
undocumented calibration procedure.

Failing that, any suggestions on physically modifying one to drop the float
level a bit? I've thought about changing the thermistor circuit to fool the
UPS into seeing a higher internal temperature (charging is supposedly
temperature-correlated), but then it would probably run its fan constantly.

APC Smart-UPS ... battery float voltage adjustment?
 

"stu" wrote in
:

Put all this in brackets and label "l think". l am sure someone will
yell at me if l have it wrong.
Dpends on how "smart" the charger is, if it is just a float charger
and doesn't monitor the battery voltage and you wanted to drop the
float voltage to about 13.2V a diode in the charge cable will do it.
there are different sorts of diodes that will give you a lower voltage
drops. but the "normal" diode is about 0.8V drop(l think)

just an idea
don't be afraid to yell at me if l am wrong.




You're right. In the past I have put a diode in series with a charger and
readjusted the float to compensate for the drop. This was to prevent the
charger from draining the battery during a power failure.

Tim

APC Smart-UPS ... battery float voltage adjustment?
 

Bob Adkins wrote:
On Tue, 1 Jul 2003 21:34:11 +1000, "stu" wrote:


Put all this in brackets and label "l think". l am sure someone will yell at
me if l have it wrong.
Dpends on how "smart" the charger is, if it is just a float charger and
doesn't monitor the battery voltage and you wanted to drop the float voltage
to about 13.2V a diode in the charge cable will do it. there are different
sorts of diodes that will give you a lower voltage drops. but the "normal"
diode is about 0.8V drop(l think)


Don't you mean a resistor?

Bob

He certainly does NOT! Many diodes will drop the voltage by
0.4 ~ 0.5vDC when forward biased.

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Sealed lead acid batteries recommend a charge voltage from
2.25-2.33volts/cell. This works out at the top end at 14.0v and should be
ok. Batteries typically last about 3 years based on the frequency of
discharges, the duration of discharge and the ambient temperature. The best
thing you can do is make sure the battery/UPS is kept at 77 degrees F.

The diode option will not work because it is directional and the battery
needs to work in both directions (charging when utility is present and
discharge when the UPS is on battery).

"Browntimdc" wrote in message
...
"stu" wrote in
:

Put all this in brackets and label "l think". l am sure someone will
yell at me if l have it wrong.
Dpends on how "smart" the charger is, if it is just a float charger
and doesn't monitor the battery voltage and you wanted to drop the
float voltage to about 13.2V a diode in the charge cable will do it.
there are different sorts of diodes that will give you a lower voltage
drops. but the "normal" diode is about 0.8V drop(l think)

just an idea
don't be afraid to yell at me if l am wrong.




You're right. In the past I have put a diode in series with a charger and
readjusted the float to compensate for the drop. This was to prevent the
charger from draining the battery during a power failure.

Tim

Read again what Tim said, not what you thought. Of course it works.

"stu_e" wrote in message =
...
=20
The diode option will not work because it is directional and the =
battery=20
needs to work in both directions (charging when utility is present and =

discharge when the UPS is on battery).
=20
"Browntimdc" wrote in message=20
...

You're right. In the past I have put a diode in series with a charger =
and
readjusted the float to compensate for the drop. This was to prevent =
the
charger from draining the battery during a power failure.

Tim=20

On Thu, 9 Dec 2004 14:49:37 -0500, "stu_e" wrote:

Sealed lead acid batteries recommend a charge voltage from
2.25-2.33volts/cell. This works out at the top end at 14.0v and should be
ok. Batteries typically last about 3 years based on the frequency of
discharges, the duration of discharge and the ambient temperature. The best
thing you can do is make sure the battery/UPS is kept at 77 degrees F.

The diode option will not work because it is directional and the battery
needs to work in both directions (charging when utility is present and
discharge when the UPS is on battery).

If the diode is in the charging circuit only, it will work, but if it
is also in the load circuit it will not. Not sure how the SmartUps is
set up.

"Browntimdc" wrote in message
...
"stu" wrote in
:

Put all this in brackets and label "l think". l am sure someone will
yell at me if l have it wrong.
Dpends on how "smart" the charger is, if it is just a float charger
and doesn't monitor the battery voltage and you wanted to drop the
float voltage to about 13.2V a diode in the charge cable will do it.
there are different sorts of diodes that will give you a lower voltage
drops. but the "normal" diode is about 0.8V drop(l think)

just an idea
don't be afraid to yell at me if l am wrong.




You're right. In the past I have put a diode in series with a charger and
readjusted the float to compensate for the drop. This was to prevent the
charger from draining the battery during a power failure.

Tim

I have an APC like this as well, it seems to eat batteries rather
frequently.
I don't suppose they publish a schematic anywhere...