Insights & Tips

Warm Weather Battery Charging

June 09, 2015 | Technical Info,

Temperature Compensation

When the temperature probe is connected to the Majortel DC rectifier system, the controller will perform voltage control based on air temperature around the probe for effective battery charging. The insulated probe should be installed on or near the battery post for best results and accurate temperature compensation operation.  If the probe is not connected to the power system this battery charger feature will not operate.  Temperature compensation has an inverse relationship to voltage control, therefore, a warmer increase in temperature results in a compensated lower DC charge voltage.  A lower charge voltage means less heat dissipation in the battery.

Temperature coefficient setting

Obtain the temperature coefficient in mV/°C for floating charge from the battery supplier or input operation parameters manually. Verify proper probe operation by monitoring the measured temperature on the MTS-Com screen. Input the coefficient value in mV/°C and reference temperature in °C for the battery parameters under the controller menu.  Factory default settings are center temperature 25°C and 3mV/°C per cell; based on string size. The center temperature setting range is available from 10°C through 40°C.  Temperature compensation is only active for a temperature within the feature range. The range of settings for XXmV/°C is 0-500mV. User applications may change based on actual battery chemistry and manufacturer recommendations. Assume a 2.25 volt per cell battery for the illustrations below.

Float charge value calculation

When the air temperature(ambient probe), near the battery, is higher or lower than the reference (normally 25°C temperature) the float charge voltage will change using the temperature compensation calculation.  Temperature has an inverse relationship to voltage control in the Majortel DC power system. A) The Set Point voltage(Vfc) @ reference temperature = Float charge voltage on the bus B) The Vfc +/- temperature coefficient = temperature compensated Vfc

For example, the chart below contains sample voltages for a range of temperatures  based on 25°C center set point; offsets of +10 degrees and -5 degrees.
48V system set point for a 24 cell string and 54 Vfc. with a 72mV/°C coefficient a string.3mV x 24 cell = 72mV/string for each degree
A) Set Pt Vfc T °C Comp Δ B) Final Vfc
35(+10) -0.72V 53.28
54.00 25  0.0 54.00
20(-5) +0.36V 54.36
24V system set point for 12 cell string and 27 Vfc. with a 144mV/°C coefficient a string.3mV x 12 cell = 144mV/string for each degree
Set Point Vfc T °C Comp Δ Final Vfc
35 -1.44V 25.56
27.00 25  0.0 27.00
20 +0.72V 27.72
130V system set point for 60 cell string and 135 Vfc. with a 180mV/°C coefficient a string.3mV x 60 cell = 180mV/string for each degree
Set Point Vfc T °C Comp Δ Final Vfc
35 -1.80V 133.20
135.00 25  0.0 135.00
20 +0.9V 134.10
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