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HomeTips & GuidesMomentary Start Switch: How It Works and Compares to Latching Switches

Momentary Start Switch: How It Works and Compares to Latching Switches

Although most people prefer push-button ignitions, old folks are more accustomed to key-start ignition systems. Key start ignition interfaces feature momentary start switches as the underlying technology. 

This switch completes the electrical link that powers the starter relay to run the starter. 

And since it is momentary, it has a spring that pushes the key back to the original position once the engine starts.

Let’s look at how this switch works and its comparison to the push-to-start switch.

Table of Contents

What Is a Momentary Start Switch?

A momentary start switch is a two-state switch in the OFF position by default (when not pressed). 

When you depress the switch button or lever, it goes into the ON state, allowing power to flow through the circuit.

Let’s focus on automotive applications.

This pushing activates the switch to send power to the starter relay, which powers the starter motor.

A vital defining feature of this engine is it does not latch in the depressed state. Therefore, the switch goes back off when you release the button or lever.

If you’ve driven a vehicle with a key-start ignition, you must have noticed the ignition has four positions. These are Off (Lock), ACC (Accessory), On, and Start.

The positions of a key-start ignition switch

The positions of a key-start ignition switch

You only use the last position (start) to ignite the engine. Once it is on, the switch returns to the On position. 

Therefore, the momentary start switch sits between the On and Start positions.

Key-Start Switch vs. Keyless Push-Button-Start Systems

The primary difference between the two is in the momentary vs. latching mechanisms. 

Key-start switches feature momentary start switches that only engage the starter motor via the relay when pressed.

But push-button ignition switches operate differently. If you’ve driven a car with this ignition type, you must have noted that it does not have four positions like the keyed type.

Instead, the button has a latching mechanism. Therefore, it maintains the On state when you depress it. So, you must press and release it to change its state from On to Off.

How Does It Turn On the Engine Without Keeping the Starter on Throughout?

Regardless of the ignition mechanism, the starter only requires power for a short period to crank the engine.

 However, the automotive push-button switch has a latching mechanism that keeps the switch on. How does it cut power to the starter relay?

Well, the automotive switch operates slightly differently. The button does not send power directly to the relay.

A push-to-start ignition system

A push-to-start ignition system

These systems must have a key fob for authentication. The button cannot start the vehicle if this fob is not within range. 

This fob usually has a transponder or RFID chip that the vehicle’s computer uses for authentication. Usually, it turns the button green.

The push button switch will only turn on the accessories without depressing the brake pedal; the engine will remain off. 

This brake pressing is a safety feature to ensure the vehicle is in a safe condition.

But when you depress the brake pedal and push the push-to-start button, it sends a signal to the computer. 

This onboard module checks the key fob signal to confirm it is within range (in the vehicle). Once verified, the module transmits a signal to the starter motor to crank the engine.

What About Push Button Starter Switches?

You might find push buttons with momentary start switches in some automotive units, especially race or high-performance cars. These vehicles require this ignition-type switch for quick engine starting.

Miniature micro momentary tactile push-button switches

Miniature micro momentary tactile push-button switches

The devices operate like key-start switches because they complete the starter relay circuit momentarily. When you release the button, the switch cuts off power to the relay.

Common Applications of Momentary Start Switches

These switches have multiple applications outside the scope of vehicles because you can find them in the following areas.

  • Consumer electronic devices
  • Medical devices
  • Aviation and aerospace
  • Medical devices
  • Boats
  • Construction machines
  • Agricultural equipment
  • Elevator control buttons
  • Control panels
  • Instrumentation

Advantages of Momentary Start Switches

These power/signal control devices have the following benefits.

Reduced Wear and Tear

Compared to their latching counterparts, momentary start switches only make contact briefly. 

When you release the button or lever, the switch disconnects the circuit. 

This operating mechanism reduces wear and tear on the switch, making it last longer than the latching type.

A momentary switch

A momentary switch

Prevents Accidental Activation

Since the switch does not latch, it is less prone to accidental activation. Even if you press the button accidentally, you cannot leave it on. 

The activation must be intentional. But latching mechanisms can remain on by accident, causing safety hazards.

Momentary Start Switch: Introduces a Security Layer

Holding down a button or turning a key to activate a car or machine adds a security layer. Unauthorized persons will have a difficult time trying to start the vehicle.

Gives Better Control

Momentary start switching gives better control and precision over the activation process. 

This feature is critical where you need brief, regulated activation controls, such as when running assembly-line motors from control panels.

A momentary push button switch

A momentary push button switch

Integrates Easily with Modern Technology

These switches can integrate seamlessly with digital and electronic interfaces like touchscreens.

Momentary Start Switch: Convenient UI

These start switches are intuitive and user-friendly, especially if they have a push-button activation mechanism. 

Key-start momentary switches in vehicles and control panels are intuitive, as well.

Adaptable in Various Applications

Lastly, momentary switches are versatile enough to work in multiple applications, including automotive, industrial, and agricultural machinery, control panels, etc.

Red and black momentary switches

Red and black momentary switches

Wrap Up

Although momentary start switches are usually synonymous with vehicle starting (automotive switches), their applications extend far beyond this scope.

Therefore, consider using them for the other momentary switching applications listed above to make the interface more intuitive and user-friendly.

Contact us if you need these electrical switches and automotive wire harnesses, and we’ll show you how to get them at reasonable prices.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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