How Does Car Start/Stop Technology Work?

Starting a car eats up more fuel than letting it idle for an hour. While cold starts tend to suck down a fair amount of gas when you first turn the ignition key, it’s the exact opposite when the engine is at optimal running temperature.

This is why so many new car manufacturers are incorporating start/stop technology into their automobiles. The Society of Automotive Engineers ran a study that found that modern stop/start systems actually help increase fuel economy by over eight percent when running in heavy traffic. Over time, this can add up to a tremendous amount of fuel—and money—savings.

Read on to learn more about how to stop/start technology works and one critical component of that system that uses more power than you may realize.

 

Start/Stop Technology

While each car manufacturer has its own proprietary system, they all work very similarly. When you apply the brakes, and your car comes to a complete stop, the ECU cuts both fuel and spark, thereby instantly shutting the engine down. When you take your foot off of the brake, the computer re-engages the fuel and spark, and your car starts right back up.

One of the initial downsides to early start/stop technology was that it tended to put a strain on the starter motor from a mechanical perspective. Automotive manufacturers realized this early on and solved the problem by beefing it up to withstand hundreds of thousands of on/off cycles.

 

A car’s start-stop button (keyless ignition).

 

The Start/Stop Car Battery

A vital component of the stop/start technology is the car battery. This is because the starting process requires a considerable amount of energy to provide power to the spark plug, which allows the engine to turn over.

Just one trip running errands around town will require your engine to start and stop many times over. A standard starter battery (SLI) is not designed to turn a car off and on multiple times in a relative quick succession, or continuously charge and discharge it.

Once the car is turned over, the generator takes over and provides on-demand power to the assorted electronics, such as the navigation and infotainment system. This means that there is no charge being sent back to the battery when the generator is operational.

Bottom line: if you were to have a standard car battery powering the stop/start technology inside your car, it would get depleted in a very short period of time. Your run-of-the-mill standard auto battery just isn’t going to cut it.

 

Why You Need a Superior Battery

Consider the last time you left your house to run some errands. You probably got stuck at a few traffic lights along the way. While your car’s engine is technically turned off, the infotainment, computer, and other electrical systems still require power.

The load is further increased by continuous stopping and starting of the engine. In short, driving short distances puts a heavy strain on car batteries. This is compounded in cold climates where the battery will outright refuse to accept a full charge.

It’s recommended that you only use superior performance AGM batteries, such as those from Houny Battery when replacing the battery on your stop/start car. There are three distinct advantages to an AGM battery powering your vehicle:

1. Balanced Charge State – In most modern vehicles, an AGM battery is powered by a generator and fed energy from the braking energy recovery system. Unlike standard car batteries, which need to be kept fully charged at all times, an AGM battery can operate in a partially charged state and still provide extra capacity to store the braking energy.

2. Superior Cold Starts – AGM batteries provide a substantial cold start current. They reduce the running time of the starter motor by providing a powerful boost of energy. Due to the inherent cycle stability, they can stop and start the engine many times over without the risk of problems arising.

3. Excellent Reserve Capacity – AGM batteries have a high reserve capacity. This means they can provide the high-power demands required by today’s modern vehicles no matter what state of charge they’re in. In short, an AGM battery is way more efficient than a standard car battery.

 

Why is my car’s start-stop system not working?

My car has a start-stop system, which seems to activate less frequently these days.

When it used to activate more frequently, I noticed a small improvement in my car’s fuel economy.

Under what circumstances would the system not work?

As a fully automatic function, the start-stop system allows only one driver-input, which is to turn it off or deactivate it completely with a dashboard button that is provided on all cars with this feature.

At all other times, the feature is controlled by its electronic controller.

In normal operation, the system shuts off the engine whenever the car comes to a standstill (or in some cars, almost at a standstill).

However, this will occur only if the electronic controller has checked a number of parameters and confirmed that the start-stop function can be activated.

For example, the engine must be at its normal operating temperature, the interior climate has to have a suitable temperature and humidity, the battery’s condition is at an optimum voltage and the braking force at the instant the car is at a standstill should be enough.

All these “check boxes” must be ticked for the start-stop system to kick in.

For instance, if the car’s battery is approaching its end-of-life and the voltage is hence not up to the value recognized by the electronic controller as “okay” for start-stop operation, the said function will not be activated.

If you need to change the battery on a car with the start-stop feature, make sure the correct type of battery (specified in the owner’s manual) is installed.

Batteries meant for start-stop systems are capable of sustaining voltage over a higher frequency of starts and are different from regular lead-acid batteries.

Accessories such as powerful audio systems and certain in-car cameras may demand high enough power from the battery to cause the minimum voltage to be unsustainable for continuous start-stop function.

Also, on a very hot day, when the air-conditioning system is called upon to maintain a comfortable interior temperature for the occupants, the engine will not shut down, so as to keep the air-conditioning compressor running and ensure that the ventilation system can deliver cool air inside the cabin.