The Difference Between Hard Start And Soft Start

Hard starters and soft starters are extremely valuable in protecting your motor and applications from the uncontrollable inrush of current that is created when you start up your motor. They can both be used to protect the motor and appliances to an extent, but both do this in very different ways.

Today we’ll be comparing the hard starter and the soft starter, considering what they both are, how they work, and the benefits and drawbacks of each.

What is a hard start?

A hard start is where the inrush of current is spiked to reduce the time taken to get a system started up. You can use a hard start when your electrical current needs a boost to get the motor starter.

The inrush of current is heightened which can put your motor at risk of overheating or suffering a shorter lifespan.

Hard starters are most helpful when it comes to large AC units within residential or commercial buildings. You can use hard starters when you have a powerful power source that is able to offer your AC unit motors enough power to manipulate the inrush of current enough.

A hard start kit includes a start capacitor and a start relay. Plug the hard start kit onto the run capacitor with two wires, incredibly easily and quickly. You’ll need no professional to help with this installation. Hard starters begin at a mere $10 online, so they’re worth a try if your AC is not turning on properly.

Many people are surprised at how simple the fix is to install an inexpensive device into the system before starting it up. Your motor will begin as soon as the hard starter is installed, so you can get your system fixed within minutes.

What is a soft start?

On the other hand, a soft start is used to protect the motor and your appliances from a shorter lifespan. The soft start reduces the inrush of current by up to 70%, reducing the potential damage from occurring and allowing the motor to startup more smoothly and safely than a hard start.

Soft starters are best used when the power source is a small generator. For example, soft starters can be used in RVs when you need an AC unit working but you don’t have access to mains power. A hard starter will not work with a small generator, so they are useless in an RV powered by a generator.

A soft starter also contains a start capacitor and a start relay like the hard starter. However, the soft starter also uses comprehensive electronics with impressive algorithms that can sense and record numerous things in the startup of your motor.

How does a hard starter work?

A hard starter works by storing energy in a capacitor. Once you try to turn the motor on, the energy from the capacitor will be released and join with the initial inrush of current to amp it up and get the struggling motor going.

You will be able to hear when your AC is hard starting by listening closely. Once you turn on the AC, if you hear stuttering or clicking sounds paired with the AC not staying on for too long, it could indicate that the AC needs a hard start kit.

When starting up an AC, the compressor often needs 4 to 8 times more electrical current to allow it to startup. Over time, this additional power can overheat the system and shorten its lifespan considerably.

A hard start kit can shorten the startup period of the motor and reduce the amount of electrical current needed to start your AC up. Without a hard starter, the electrical efficiency will only be around 50%. However, a hard starter can see this rise to up to 98%.

While the hard starter can protect your motor to a certain extent, it still allows a lot of power to race to the motor all at once. This is bound to reduce the lifespan somewhat, so a hard starter is still not as protective as a soft starter.

How does a soft starter work?

A soft starter works by controlling the amount of voltage running through the circuits of a motor. The soft starter can do this by affecting the torque of a motor, which reduces the voltage and allows it to manipulate the voltage to allow for a smooth startup and acceleration.

The majority of modern soft starters now use Silicon Controlled Rectifiers (SCRs) or thyristors to limit the voltage more effectively. Once the motor starts up, the SCRs turn on and limit the voltage able to reach the motor.

Once the motor begins to accelerate, the SCRs begin to relax and allow more voltage to reach the motor. After all of the voltage is allowed to reach the motor, the SCRs will turn themselves off. Soft starters tend to have an efficiency of 99% or higher.

Soft starters can protect the motor and circuits from the initial inrush of power, extending the lifespan of these components. Soft starters can protect against overheating. AC units are also known for their thumping noises, which the soft starter can prevent once installed.

When should a hard start kit be installed?

There are a few reasons why you might need a hard starter, which we have detailed below.

Your AC is hard starting already

We mentioned earlier how you might be able to tell whether your current AC is hard starting or not. Here they are again, as well as a few new indications to look out for:

  • The AC starts but then shuts off soon thereafter – or short-cycling, which usually indicates something wrong with the compressor.
  • There is a clicking noise as the compressor starts, which is another indication of something wrong with your compressor.
  • The lights flicker when you turn on the AC, which shows that the AC is draining too much power to get started.
  • The compressor trips your circuit breaker, showing that too much energy is being used to start up and causing the entire circuit to trip before any electrical damage can occur.

These are four symptoms of a hard starting AC unit. Bear in mind that all of these symptoms don’t need to be present to mean that your AC is hard starting, just one symptom may be present. You might want to call a professional to help you realize your next steps.

If the compressor is at the end of its life, you will need a new one installed or to purchase a new air conditioner altogether. However, if the compressor is struggling to turn the motor on, installing a hard start kit could fix this issue without having to spend a lot on a new AC.

You have purchased a new air conditioner

Many older AC units used to come with hard start kits already installed, but newer models do not have these commonly. Make sure that you ask wherever you’re purchasing your air conditioner from whether the model has a hard starter already installed or not.

If the answer is not, you might want to purchase and install one to prevent any issues from occurring with your AC. The last thing you want is to be stuck with an AC unit that can’t start up or stay on for an extended period of time during the hottest days of the year.

When should a soft start kit be installed?

A soft starter should be installed when you need to control the torque and starting current during starting and stopping a motor. Once the motor is running, the speed will be constant until it’s turned off. Soft starters leave you with a simple, economical solution for your motor.

Soft starters can be used for conveyors and fans that need a constant speed throughout their usage. However, soft starters can also be used in RVs when you want to power the AC unit on without damaging your small generator.

Small generators typically don’t have enough power to startup an AC unit on their own. Without a soft starter, you’d need the generator to offer 4 to 8 times more power than the AC usually would need.

While achievable, this generator will be expensive and probably too large for your RV. So, soft starters can be installed to protect the AC unit and generator to start the cooling mechanism up without using an inrush of power.

While a hard starter might be best suited for large buildings with impressive AC systems, soft starters can be a saving grace when your power source is considerably smaller. An example is when you’re away from mains power or an RV hookup.

Benefits and drawbacks of hard starters

There are benefits and drawbacks to both hard and soft starters, which we are going to look into in the next two sections.

Hopefully, these sections will help you to determine whether you need a hard starter or a soft starter for your applications.


Hard starters are often considered the best option when an application needs a high starting torque to get started. Hard starters are also often much more accessible than soft starters, making them less expensive than the latter option.

While this is an attractive quality, you should take into consideration more than just the cost of your starter. Purchasing a cheap model could harm your motor and devices if you need a soft starter more than a hard starter.


Hard starters are only usable in normalized conditions. If something goes wrong or changes these conditions, the hard starter might not be able to start your motor. What’s more, this could damage your motor and AC appliance and cause it to fail completely.

For this reason, hard starters should only be used in residential, commercial, or industrial buildings that can be kept in ‘normal’ conditions. Hard starters are not suitable for RVs or motorhomes where conditions are always changing.

Benefits and drawbacks of soft starters

Much like the benefits and drawbacks of hard starters, there are many that come along with the soft starter.


Unlike hard starters, soft starters reduce the initial torque of the motor so that the torque can’t put too much unnecessary pressure on the motor or your devices. This can prolong the lifespan of your motor and the circuits.

Soft starters are designed to reduce the starting current of the compressor by controlling the current running through the start and run windings. This gives you more control over the current and therefore can protect more of the circuit from overheating.

Many soft starters also come equipped with built-in features that protect the compressor under unforeseen circumstances. This gives them the advantage over hard starters that need the conditions to remain the same.

This makes it understandable why soft starters are the best option if you’re living off the grid with a small generator or for inverter-based HVAC applications.

Soft starters are also quieter to run and often last longer than hard starters, and they can also be used to protect you from the thumping that you hear from AC units throughout the day and night.

The final benefit of soft starters is that they have been proven to give back your return on investment several times over thanks to the generator savings that they offer and preventing you from having to replace your compressor.


Soft starters are often more expensive than soft starters, and you won’t be able to find them as easily as hard starters. While the price is often a key feature to look for when shopping for anything, don’t simply choose a hard starter because it’s the cheaper option.

Soft starters might not be the best option for large AC systems or other applications that require a large inrush of current to get started.


As you can see, hard starters and soft starters are two completely different concepts. Hard starts aim to make the inrush of current as large as possible while the soft start lowers the inrush of current as much as possible.

Both are impressive in their own way, but be careful that you don’t get the wrong one for what you need. Hard starters are best used in places where the normal conditions do not change often.

Soft starters are much more flexible and can be used in RVs and motorhomes where the conditions are uncontrollable. Make sure that you do your research before purchasing one and, if in doubt, consult a professional to ensure you opt for the correct starter.