Power plant on board

The electricity source in a vehicle is the generator, while the devices such as starters, fans, controllers, lamps, and heaters are the consumers. The battery acts like a bank card that gets charged every time the engine starts and is replenished by the generator. If this does not happen, the battery may quickly deplete and the vehicle will lose the ability to start again. This mirrors real life where spending more than one earns leads to a depleted balance.

If the battery runs low, the culprit is often the generator. In slow traffic or long jams it can struggle to supply all electrical loads at once, leaving the battery short on power.

Old machines can’t handle it

Is there enough generator capacity to power all systems such as headlights, windscreen wipers, and heating when the engine idles? Decades ago, a car magazine tested endurance in vehicles like the Volga GAZ-3110 with the ZMZ-4062 engine and the Zhiguli VAZ-2104. The results showed that at idle, many generators could not meet all electrical demands, causing the battery to discharge. The same scenario occurs in slow traffic when lights, fans, and audio operate while the generator barely spins.

With modern layouts, vehicles that sit in traffic show higher energy use. Editors at Largus checked a car with about 136 thousand kilometers on the clock. They warmed the engine and turned on everything feasible, from high beams to wipers. Yet the on-board voltage stabilized at 13.2 V and the battery remained charged.

Do generators reliably supply power to all loads when another vehicle operates at idle, or does the battery tend to discharge in those conditions? Industry representatives were consulted for answers.

Manufacturer perspectives

Jaguar Land Rover

These brands employ a system that continuously monitors battery charge. If the battery is weak, certain vehicle functions may be limited to prevent deep discharge and to ensure reliable starting.

Hyundai

The electricity balance is computed during design and depends on many factors. Designers do not guarantee uninterrupted operation of every system for an unlimited time.

Mazda

There will be no battery discharge under normal operation.

Renault

A healthy alternator supports standard operation. If something goes wrong, a warning appears to alert the driver.

Volvo

The generator management in the engine control unit continually provides the required charge and adjusts engine operation based on power loads from connected systems.

Kia

Battery discharge is not expected under typical conditions.

VAZ

In a warm, well-maintained car, at idle, the generator powers standard loads and preserves the battery for a future start.

These responses suggest caution about always having enough power for every load simultaneously in all cars, including premium models.

Denis Zagarin, head of the NAMI Test Center, notes that there are no separate generator standards for energy balance or generator units beyond general vehicle requirements.

Expert commentary

There are no distinct rules for generators as standalone parts. If generators are treated as spare components, there are general requirements applying to their performance under environmental conditions, voltage changes, electromagnetic compatibility, vibration and shock resistance, dust and moisture protection, and insulation strength.

Jaguar Land Rover’s stance is informative but not universal for all vehicles, especially lower-cost models that may lack advanced load-shedding features.

Stock pocket not pulling?

Is it really possible to guarantee that every car can power all loads even at idle? The design assumes reasonable adequacy. A vehicle is built for driving, not idling in traffic, so generators are sized for typical use patterns that mix slow and highway speeds. Attempts to increase generator power through gear ratio changes can hasten bearing wear and add weight, cost, and fuel consumption. As load rises, the output voltage can drop, which is easy to monitor with a voltmeter. Charging can continue at a lower voltage until the battery and generator voltages equalize, after which charging slows or stops and the battery may discharge if the load remains high.

How not to drain your battery

The lower limit for a healthy voltage is around 12.7 V. If the system voltage dips under load in idle conditions, it helps to check battery terminals with the engine running at idle and many devices on. Normal operation for the electrical system is typically between 13.8 and 14.2 V. If the voltage rises to the upper range during shutdown with no signs of network issues, it indicates that under heavy load in traffic the battery cannot accept more charge and a local consumer may be sacrificed.

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