Table of Contents
2022 MG HS PHEV Electrical Systems
In the 2022 MG HS PHEV (Plug-in Hybrid), the electrical system differs significantly from a traditional petrol car. It manages its 12v battery through a high-voltage conversion system rather than a mechanical alternator.
How the 12v Battery Charges
The vehicle does not use an alternator to charge the 12v battery. Instead, it uses a DC/DC Converter.
The Process
This converter takes high-voltage power from the large hybrid traction battery and “steps it down” to approximately 14 volts to charge the 12v battery and run the car's electronics (lights, infotainment, etc.).
Intelligent Charging
The car features an “intelligent charging” function. It can automatically charge the 12v battery using the high-voltage battery even when the car is parked, provided the high-voltage battery has enough juice. This ensures ther is enough power to “wake up” the car’s computers and start the system.
Does it have an Alternator
No. Ther is no traditional belt-driven alternator attached to the engine. In most PHEVs like the MG HS, the DC/DC converter completely replaces the alternator’s job. This reduces mechanical drag on the engine and improves fuel efficiency.
Does it have a Starter Motor?
No, not in the traditional sense. * Motor Generator: Instead of a separate small starter motor that engages a flywheel, the MG HS PHEV uses its powerful Integrated Starter Generator (ISG) or the main electric traction motor to spin the petrol engine up to speed.
Seamless Transition
This allows the engine to start much more quickly and smoothly than a standard car, which is necessary for the constant switching between electric and petrol modes while driving.
| Component | Status | Description |
|---|---|---|
| Alternator | None | Replaced by a DC/DC Converter that draws power from the high-voltage hybrid battery. |
| Starter Motor | None | Engine is started by the Integrated Starter Generator (ISG) or the main electric motor. |
| 12v Battery | Present | Still used to boot ECUs and power low-voltage systems; charges via the DC/DC converter. |
Key Feature: Intelligent Charging The MG HS PHEV can automatically charge the 12v battery from the traction battery while the vehicle is parked to ensure the system can always “wake up.”
Note: If you find the 12v battery is flat, the car will not start even if the big hybrid battery is full, because the 12v system is needed to “close the switches” (contactors) that engage the high-voltage system
Why it doesn't charge while "Charging the Big Battery"
As you noticed with your multimeter, when you plug the car into a wall charger, the 12v battery often sits at 12v (not 14v). This is because:
- Prioritization: The car focuses on charging the big battery first.
- Logic Gap: MG's software often disables the “Intelligent 12v Charging” while the car is actively being charged by the wall
- The Result: If you leave the car plugged in for days without driving it, or if you leave the doors open while it's charging, the 12v battery can actually go flat because it isn't receiving that 14v “top-up” from the converter.
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