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An electronic starter-alternator is a reversible motor-generator: it starts or assists the engine like a motor, then generates electricity as the vehicle slows. In many mild hybrids, a 48-volt belt-integrated starter-generator replaces the conventional alternator and works with a 48V battery, power electronics, and the car’s 12V electrical system.
What is an electronic starter-alternator?
It is one electrical machine that can operate in two directions. When powered by the vehicle’s electrical system, it turns the engine or adds torque. When driven by the engine, it produces electricity. This is why a starter-alternator is more than a conventional alternator with a new name: its motor function is part of the system’s design.
Valeo describes its 48V iBSG as a belt-driven reversible starter-generator fitted in place of the alternator. Bosch describes a combined starter-generator connected to a 48V battery; in some designs it occupies the conventional belt-driven generator position. The specific layout varies by vehicle.
How does a 48V starter-generator work?
It recovers energy while slowing down
During braking or deceleration, the engine turns the starter-generator, which produces electricity. The system stores that energy in a 48V battery instead of letting all of it become heat at the brakes. The battery can then supply energy for engine restarts, torque assistance, or vehicle electrical loads.
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- H5H9 HQ9 1.8T 2.0T mild hybrid electric vehicle 48V 85A belt starter generator.
- Reversible motor: starts the engine, generates 48V voltage, assists in boosting, and regenerates braking.
- Replace IBSG4W046, 9100210DB01, 9100210DB01A.
- Built in power electronic equipment, 4-point installation, V-shaped ribbed pulley.
- Disconnect the 48V battery. Wait for 5 minutes. Code using diagnostic tools after installation.
It restarts the engine and can assist acceleration
When the engine needs to start, the machine switches to motor operation. Depending on the vehicle’s control strategy, it can also add torque during launch or acceleration, helping fill in while the combustion engine responds. The system can support smoother stop-start operation, engine-off coasting, and reduced engine load.
It connects the 48V system to 12V equipment
Most conventional vehicle electrical equipment operates on 12 volts. A DC-DC converter supplies the 12V network from the 48V system, allowing the mild-hybrid components and the vehicle’s lower-voltage electrical loads to work together.
Rank #2
- Compatible with GC9, Epro, OKAVANGO and models 01/02/03, equipped with a 1.5T 48V mild hybrid system.
- 48V, 60A belt-driven starter generator (BSG). Integrates starter, alternator and energy recovery functions.
- Key components of the 48V MHEV system: supports automatic start-stop, electric assistance and regenerative braking, providing a stable 48V output.
- Suitable for bolt-mounted installation of model 11601324 / 2040010000. The installation position and electrical connectors are the same, no modifications required.
- 48V high-voltage components. Installation requires operation by technicians certified for hybrid systems. Before maintenance, disconnect the 48V battery.
What performance figures are published?
Published specifications describe particular products or architectures, not a guaranteed result for every mild hybrid. Valeo’s 2024 figures for its referenced 48V iBSG product family include:
- Up to 6% fuel-economy benefit on the WLTP cycle compared with a conventional stop-start system. This is Valeo’s product claim, not a universal real-world saving.
- Peak regenerative braking power up to 15 kW and peak mechanical power up to 10 kW.
- Maximum torque above 65 Nm and efficiency above 85%.
- More than 1 million stop/start operations.
Separately, STMicroelectronics describes 10 kW as a typical figure for a belt-driven starter-generator. It is an architecture-level typical value, not a rating that applies to every unit.
Rank #3
- It provides stable power to the vehicle's electronic equipment and efficiently charges the battery, ensuring long-term stable vehicle operation.
- It ensures normal engine operation, prevents short-circuit failures, and supplies power to all electrical equipment except the starter motor.
- Made of high-quality materials, it is wear-resistant, corrosion-resistant, high-temperature resistant, and vibration-resistant, making it robust, durable, and not easily damaged.
- No vehicle modifications are required, allowing you to quickly and easily get your vehicle back on the road.
- Please carefully check the compatibility of this product with your vehicle before purchasing. If you have any questions, please contact us immediately, and we will resolve them for you as soon as possible.
How does it differ from a conventional alternator?
A conventional alternator generates electricity when the engine drives it. A starter-alternator can also act as a motor, so the system can use stored electrical energy to restart the engine or provide torque assistance. The 48V mild-hybrid version adds a battery and associated power electronics; it does not, by itself, mean the vehicle can drive as a full battery-electric car.
What should you check before replacing one?
Do not choose a part based only on a listing that says “hybrid alternator.” Fitment depends on the vehicle and its complete electrical and mechanical arrangement. Identify the vehicle’s year, make, model, engine, 48V architecture, and original-equipment part number, then verify the details below against vehicle-specific parts and service information.
Rank #4
- 100% New Aftermarket Part - all of our units are manufactured to meet or exceed OEM specifications
- Specs: Starter, Voltage: 12, Rotation: CW, MTG Type: Flange, Num MTG Holes: 2, Starter Type: OSGR, KW: 2.2, Number of Teeth: 9, Gear OD: 1.417in / 36mm, Mtg Ear 1 Hole: 13mm Unthreaded, Mtg Ear 2 Hole: 13mm Unthreaded, Wet Clutch Seal: No, Weight: 11.12 lbs / 5.05 kg
- Replaces OEM Part Numbers: Hitachi: S13-407A, S13-407, Lucas Electrical Europe: LRS02763, Thermo King: 45-2711, 45-2324, 845-2324, 845-2177, Unipoint: STR-6019, STR-6007, Wood Auto: STR72213
- We want to make sure that you get the correct part for your application - please use the part information below to verify that this is the correct replacement for your vehicle. If you need assistance, please contact us.
- We are committed to ensuring that our customers are satisfied with their purchase which is why all of our parts are backed by a 1-year warranty to protect you in the event that there are any issues with your order
- Belt routing and width, plus the pulley or decoupler design.
- Electrical connector and wiring, battery, inverter, and DC-DC converter compatibility.
- Cooling arrangement, belt tensioner, and control-system integration.
- Whether installation requires vehicle coding, calibration, or other model-specific steps.
- Availability of the correct vehicle-specific service parts.
A generic marketplace listing can be a lead, but it is not proof of compatibility. A mismatch in the belt drive or electrical and control interfaces can make a part unsuitable even if it is described as a 48V starter-generator.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can you replace a hybrid starter-generator yourself?
There is no safe universal replacement procedure: access, electrical isolation, belt removal, installation, and any required calibration depend on the vehicle. The system includes a 48V battery and power electronics as well as the belt-driven unit, so do not treat the job as an ordinary alternator swap. Valeo Service warns that incorrect removal or installation can damage the component or injure the technician. Use the vehicle-specific service procedure and have the work done by a qualified technician if you do not have the required training and equipment.
Quick Recap
Best Value
- BVWBCR Self Starter Motor Compatible with AUDI A6 C8 Avant A7 A8 D5 Q7 Q8 3.0T Mild Hybrid 2018- 06M911022 06M911022X 438349 12V
Sources
- Valeo, “48V Belt Starter Generator (iBSG),” updated 12 July 2024
- Bosch, “Here comes Bosch’s 48V hybrid battery”
- STMicroelectronics, “48 V Starter Generator” brochure
- Valeo Service, “What is the belt integrated starter generator (iBSG) in a 48v system?”
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
