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

Discussion in 'Electronic Repair' started by Jordan Hazen, Jun 30, 2003.

  1. Jordan Hazen

    Jordan Hazen Guest

    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.
     
    Jordan Hazen, Jun 30, 2003
    #1
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  2. Jordan Hazen

    Browntimdc Guest

    "stu" <> wrote in
    news:3f0171ba$0$5431$:

    > 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
     
    Browntimdc, Jul 1, 2003
    #2
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  3. Jordan Hazen

    Bob Adkins Guest

    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
     
    Bob Adkins, Jul 2, 2003
    #3
  4. Jordan Hazen

    Jack Daynes Guest

    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.

    --
    -- Jack --
    ===================================
    The difference between intelligence
    and stupidity, is that intelligence
    has limits.
    =================================
    Clean Up Return Address To Reply
    =================================
    Poway, California (San Diego Co.)
    N 32° 57' W 117° 04'
    At 508' Elevation
    =================================
     
    Jack Daynes, Jul 2, 2003
    #4
  5. Jordan Hazen

    stu_e Guest

    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" <browntR*E*M*O*V*> wrote in message
    news:Xns93AB6FCEA68D0tbflash@207.115.63.159...
    > "stu" <> wrote in
    > news:3f0171ba$0$5431$:
    >
    >> 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
     
    stu_e, Dec 9, 2004
    #5
  6. Read again what Tim said, not what you thought. Of course it works.

    "stu_e" <> wrote in message news:...
    >
    > 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" <browntR*E*M*O*V*> wrote in message
    > news:Xns93AB6FCEA68D0tbflash@207.115.63.159...
    >>
    >> 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

    >
     
    John R. Copeland, Dec 9, 2004
    #6
  7. Jordan Hazen

    Guest

    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" <browntR*E*M*O*V*> wrote in message
    >news:Xns93AB6FCEA68D0tbflash@207.115.63.159...
    >> "stu" <> wrote in
    >> news:3f0171ba$0$5431$:
    >>
    >>> 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

    >
     
    , Dec 10, 2004
    #7
  8. Jordan Hazen

    Dave VanHorn Guest

    I have an APC like this as well, it seems to eat batteries rather
    frequently.
    I don't suppose they publish a schematic anywhere...
     
    Dave VanHorn, Dec 10, 2004
    #8
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