MACS Monthly Newsletter - 2021 - JAN4
Cabin Heater Power Controls
Cabin Heater power controls can be very
simple or elaborate, depending on the component supplier. Within the Cabin Heater
electronic controls, are power transistor systems (i.e., N-Channel Enhancement MOSFET or IGBT transistor) that are voltage conFigure 8: Graphic of a cabin heater control system and power transistors con- trolled by placing a 0 - 5V or a 0 - 12V Gate
voltage (5V or 12V = 100% PWM). Firmware
nected to a high voltage battery pack.
(F/W) that resides within a dedicated mienergized, heating causes the resistance of the heating element
crocontroller (i.e., embedded controller) will
to drop. The decreasing resistance, in turn, causes more current control how much heat is generated by the Cabin Heater (Figto flow which heats the part still further. If the voltage is high ures 9, 10). There is a difference between Software (S/W) and
enough, the unit will self-heat until it passes into the PTC region F/W. S/W systems utilize an operating system (i.e., iOS, Winof resistance.
dows, Linux, etc.). F/W doesn't use an operating system. The
Once in the PTC region, it reaches the point where I2R (or, controller is programmed with S/W by coding the F/W hardCurrent2)(Resistance), heat generated by the part is sufficient to ware using S/W program syntax commands. The syntax commake up for the loss of heat to the ambient. In this situation, the mands are then uploaded to the microcontroller. The microcondevice is in equilibrium. If it starts to decrease in temperature, troller will only execute the commands that have been uploaded
Eberspaecher
Quarto Technical Services, LLC
its resistance will decrease drawing more
current and countering the cooling tendency. Conversely, any tendency to increase its
temperature meets just the opposite effect.
In this condition, the PTC is auto-stabilized
(self-regulation) at a fixed temperature. In
summary, the PTC current is self-regulating
after it reaches operating temperature. Relative to HV Battery Pack voltage changes during a drive cycle, the constant temperature
mechanism will be effective. If the operating
voltage increases, the PTC initially consumes
more power, but as a result, its temperature
increases and thus the current becomes stabilized at a lower level.
Figure 9: Block diagram of a cabin heater control, power system, and PTC heater elements.
January 2021
4
MACS Service Reports
MACS Monthly Newsletter - 2021
Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2021
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