Electrical 2-3
Section 2: Electrical
High and Low-Voltage Systems
NOTICE: Do not backprobe or splice into the high-voltage system. Voltage in the system is
275v DC. Damage may occur to equipment added to the system.
The high-voltage system has a floating ground. When the engine is operating or the vehicle is
moving, the high-voltage generator begins to generate high voltage, AC electricity. High-voltage
AC electricity can be consumed or generated by the motor generator, the traction motor or a
combination of both motors. Excess high-voltage current is converted from high-voltage AC to
high-voltage DC electrical power inside the motor generator unit and transmitted through the
high-voltage (orange) cables. The high-voltage DC electrical power is converted to low-voltage DC
electrical power through the DC/DC converter. This low-voltage DC electrical power is then
supplied to the 12-volt battery through the low-voltage battery cables.
12-Volt Battery
The 12-volt battery is a standard automotive battery. It is a DC source connected in a negative
ground system. The battery case is sealed, with 2 vent holes to release gases. The battery has 3
major functions:
• Storage of electricity for later use
• Voltage stabilizer for the electrical system
• Temporary power source when electrical loads exceed the DC/DC converter output current
High-Voltage Traction Battery (HVTB)
NOTICE: Do not backprobe, splice or repair the high-voltage (orange) wiring. Voltage in the
system is 275 volts DC. Damage may occur to equipment added to the system.
The high-voltage traction battery (HVTB) is a 275 volts DC source connected in a floating ground
system. The battery receives, stores and delivers high-voltage electrical power when required by
the vehicle control strategy. On the HVTB there are 2 controllers: a battery energy control module
(BECM) and a battery pack sensing module (BPSM). None of the BECM or the BPSM wiring
should be tapped or spliced to check for battery voltage (power), ground or signals. There is also
the bussed electrical center (BEC) which houses the contactors, current sensor and the associated
components. The service disconnect is mounted between the BEC and the BPSM and is used to
disconnect the high-voltage from the vehicle system.
2012 Fusion Hybrid, MKZ Hybrid Modifiers Guide, 09/2011
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