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JD5003-00
The thermistor used in current production has a nominal value of 10K Ohms at 25°C, and is interfaced with
the charger microcontroller by an analog circuit, using a 5Vdc power supply. The maximum power
dissipation of the thermistor is 0.6mW, and occurs at 25°C, which minimizes self-heating effects (less than
0.4°K). Because of the adhesive tape layer, the probe has a response time of one minute or longer.
Please note that only a shielded twisted pair cable should be used, such as the cable supplied with the
probe. The shield should be grounded only at the battery charger end, as described in the installation
instructions. Never run the cable in the same conduit or trough with power wiring. If possible, run the
cable in its own dedicated conduit.
The thermistor manufacturer does not specify the dielectric strength. In factory tests, we have found that
the probe and adhesive will withstand at least 500Vdc without damage. To be safe, do not use the probe in
a dc system higher than 130Vdc (nominal).
The thermistor resistance is measured by the battery charger control circuit, and that is converted to
temperature using a linear-izing calculation.
Therefore, with the thermistor tolerance, self-heating effects, and algorithm accuracy, the temperature
measurement is accurate to within ±2°C. The calculation is linearized only between 0°C and 50°C. These
temperatures define lower and upper limits, respectively, on temperature compensation.
temperatures below 0°C, the output voltage no longer changes, and at temperatures above 50°C, the output
voltage no longer changes.
Temperature compensation affects high and low dc voltage alarm set points differently, dependent upon
utilizing compensated or uncompensated voltages. Refer to the two sections describing these differences,
starting on Page 3 of 8. If you anticipate large temperature excursions, you may need to adjust the HVDC
and LVDC alarms accordingly.
The compensation slopes chosen for lead-acid and nickel-cadmium batteries are typical values specified by
battery manufacturers. Some manufacturers specify float voltage adjustments over a limited range (such as
10° - 40°C), and may choose to specify the "room temperature" as 20°C instead of 25°C. This does not
change the slope. If you want to adjust the float and equalize voltages for the exact battery temperature as
described above, you should consult the battery manufacturer's instructions to determine the correct float
voltage value at 25°C.
There are two (2) temperature compensation slopes for the AT Series microprocessor-controlled battery
charger, which are linear between 0° and 50°C:
1) Lead Acid:
2) Nickel Cadmium: -1.9mV/V/°C (-1.1mV/V/°F) or
If you want to perform manual temperature compensation, you should first have a good temperature-
controlled environment. You may use the slopes (in the graph featured at the end of this application note)
to calculate the correct float voltage for any battery temperature.
This application note primarily covers TempCo use with float voltage. The same considerations apply to
equalize voltage. If you are using temperature compensation because of environmental requirements, never
try to equalize the battery without the temperature compensation active. This is especially true for VRLA
batteries, since thermal runaway, and consequent permanent battery damage, are possible when equalizing
at elevated temperatures.
A major goal of temperature compensation is to minimize "excess Ampere-hours" delivered to the battery
at elevated temperatures. Excess charge Ampere-hours translates to increased electrolyte loss and grid
corrosion, resulting in a reduction of battery life. Since temperature compensation does not adjust the
output voltage for temperatures over 50°C, never operate a battery in an environment warmer than 50°C
(122°F). Most VRLA manufacturers recommend the battery temperature never exceed 40°C (105°F).
JD5003-00.Rev6.doc
AT10.1/AT30 Series Battery Charger
The algorithm used has a maximum error of 1.0°C.
-2.5mV/V/°C (-1.4mV/V/°F) or
-6.0mV/cell/°C (-3.3mV/cell/°F) at 2.4VPC (Volts per cell)
-2.7mV/cell/°C (-1.5mV/cell/°F) at 1.4VPC (Volts per cell)
Page 4 of 8
Application Note
Rev. 6 - Last Printed 10/31/2014 10:31:00 PM
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