When sizing a generator for your RV air conditioner, the initial question to ask should not be “What size generator do I need to run the AC?”, but should be “What size generator will be able to start the AC?”.
As an example, let’s consider whether a 3000 Watt generator can handle your 15,000 BTU RV air conditioner:
Partial answer: Yes, a 3000 Watt generator can run your 15k BTU AC.
Full answer: Yes, a 3000 Watt generator has the capacity to run the AC. However, without a soft starter, the generator might occasionally struggle to even start the AC.
In this article, I’ll start by discussing the wattage requirements of 15000 BTU RV air conditioners, explaining how to determine this wattage, and even how to reduce it.
Once we’ve covered these aspects, I’ll guide you through using the wattage specifications of your RV AC and other appliances to accurately calculate the generator size that suits your needs.
Let’s delve into the details.
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How many watts does a 15000 BTU RV air conditioner use?
Typically, 15000 BTU RV air conditioners consume approximately 1500 – 2000 Watts of power. However, this wattage represents the “running” power when the air conditioners are operational. During the starting phase, a 15000 BTU air conditioner could potentially require anywhere from 6500 to 9000 Watts of power.
It’s important to clarify that your RV air conditioner won’t consistently use 6500 – 9000 Watts each time you switch it on. These numbers signify the maximum potential power usage your RV air conditioner is capable of.
Let me elaborate.
The main component of an air conditioner is its compressor, which is essentially a motor that compresses the refrigerant, allowing it to exchange heat.
Just like any motor, a relatively high amount of current (Amps), referred to as inrush current, will be required during startup. This inrush current only lasts for a moment, but can potentially peak at 7 times the normal current when the motor is already in motion.
The maximum inrush current that your RV air conditioner’s compressor might require during startup is referred to as “Locked Rotor Amps”, or “LRA” for short, and will typically be within the range of 55 to 80 Amps for 15000 BTU air conditioners.
For example, let’s take a look at this nameplate from a 15k BTU RV air conditioner:
For this specific unit, the maker indicates a compressor LRA of 60 Amps and a Voltage of 115 Volts.
As mentioned earlier, the “Locked” Rotor Amperage rating denotes the highest amount of electrical current (Amps) the compressor might need to get “unlocked” and begin operating.
Now, Power (measured in Watts) is the product of current (measured in Amps) and voltage (measured in Volts):
Watt = Amps x Volts
Using the air conditioner’s LRA rating and its voltage, we can work out the “potential” starting wattage of the AC:
Potential Starting Watts = LRA (Amps) x Voltage (Volts)
Potential Starting Watts = 60 Amps x 115 Volts
Potential Starting Watts = 6900 Watts
Now, it’s worth emphasizing that the unit will not necessarily require 6900 Watts whenever the compressor tries to kick on, and will usually only require around 3500 Watts.
However, to be on the safe side, and to make sure that the generator is always able to start the air conditioner, the size of the generator should be greater than the air conditioner’s potential starting wattage calculated using the LRA rating of the AC.
So, does this mean that we would need a 6900 Watt+ generator to start and run this RV AC?
Well, yes. This approach would guarantee that the generator won’t struggle during startup. However, another approach would be to install a soft starter, which would limit the starting wattage of the air conditioner, and allow us to use a smaller generator.
See, a soft-starter kit such as the MICRO-AIR Easystart 364 or the SoftStartRV could be installed on your air conditioner and reduce the potential starting wattage of the AC by 60% to 75%. This means that the size of the generator that you would need could also be reduced by up to 75%.
A smaller generator would not only be a cheaper and more portable option but would also be more efficient in terms of fuel consumption. This is because the closer a generator is to operating at full capacity, the more fuel-efficient it’ll be.
This means you’d consume less fuel per unit of energy (kWh) with a smaller generator. Learn more about this here.
Here’s a video that should provide some more perspective on these soft starter devices, how they are installed, and why you should consider using one:
Now that you have a better grasp of the power requirements of your 15000 BTU air conditioner, including methods to reduce its starting wattage, let’s explore how you can accurately select the right generator size, which involves considering your other appliances as well.
What size generator do you need to run your 15000 BTU RV AC and other appliances?
A generator’s capacity can be understood through two important wattage ratings when selecting one:
- The Running, or Rated Wattage of the generator: this rating indicates the maximum amount of power that the generator can continuously and comfortably supply.
- The Peak, Starting, or Max. The wattage of the generator: this rating indicates the maximum amount of power that the generator can briefly supply if necessary.
Typically, if your 15000 BTU RV air conditioner is fitted with a soft starter, you’d require a generator with a Peak Wattage rating of at least 2200 Watts. For this scenario, a generator like the Honda EU2200i should be enough to both start and run the air conditioner.
However, if the air conditioner lacks a soft starter, to prevent any potential issues with starting the AC, the generator’s Peak Wattage must be at least 7000 Watts.
An example of such a generator is the Westinghouse 7500W model. For better portability, another option would be 2 Westinghouse iGen4500DFc generators wired in parallel using the Westinghouse 507PC 50A Parallel Cord.
If you intend to run other appliances alongside the air conditioner, it’s crucial to ensure that the generator can manage their power requirements while starting the air conditioner.
To properly size the generator, you’ll need to ensure that its Peak Wattage rating exceeds the highest starting watts that one of your appliances might require, plus the running wattages of the other appliances that’ll be simultaneously running on the generator:
Generator’s Peak Wattage > Highest Starting Watts + Running Watts of the other appliances
Since your 15000 BTU AC’s compressor will likely have the highest starting wattage requirements of all the appliances in your RV, the formula becomes:
Generator’s Peak Wattage > The compressor’s Starting Watts + Running Watts of the other appliances
However, it’s important to note that while the compressor does account for most of a unit’s power consumption, there is another component that will be drawing power when the compressor is starting up, and that is the fan motor.
The fan motor on your RV AC drives both the condenser fan, which pushes warm air out of the RV, and the blower fan, which pushes cool air into the ducting. Though in some cases, these fans have separate motors.
In any case, you can either determine the power usage of these fans by referring to their FLA (Full Load Amperage) rating:
Power Usage (Watts) = FLA (Amps) x 115 Volts
However, a good and quick rule of thumb is to consider that these fans combined might use up to 400 Watts of power.
To visualize this, let’s imagine 2 scenarios:
Scenario 1:
Your RV AC’s compressor has an LRA of 58 Amps. At a voltage of 115 Volts, this means that it can potentially require up to 6670 Watts to start up:
Potential Starting Watts = LRA (Amps) x Voltage (Volts)
Potential Starting Watts = 58 Amps x 115 Volts
Potential Starting Watts = 6670 Watts
Let’s also make the assumption that you’d also like to be able to run the following appliances concurrently:
- A fridge that uses around 200 Watts.
- A 32in TV that uses around 60 Watts.
- A slow cooker that uses about 200 Watts.
- A few lights that in total require about 100 Watts.
- And of course, the condenser and blower fans, which combined, can draw up to 400 Watts.
The Peak Wattage rating of the generator should be at least:
Generator’s Peak Wattage > Compressor’s Starting Watts + Running Watts of the other appliances
Generator’s Peak Wattage > Compressor’s Starting Watts + Rridge Watts + TV Watts + Slow Cooker Watts + Lights’ Watts + Fans’ Watts
Generator’s Peak Wattage > 6670 Watts + 200 Watts + 60 Watts + 200 Watts + 100 Watts + 400 Watts
Generator’s Peak Wattage > 7630 Watts
With these power requirements, we’d need a generator such as the DuroMax XP8500EH, which has a Peak Wattage of 8500 Watts, and a Running Wattage of 7000 Watts.
Or two smaller generators, such as the Westinghouse iGen4500DFc generators, which can be wired in parallel using the Westinghouse 507PC 50A Parallel Cord., and would offer up to 9000 Starting Watts, and up to 6000 Running Watts.
Scenario 2:
This time, let’s say a MICRO-AIR Easystart 364 has been installed on the AC. In theory, this update would limit the starting wattage of the compressor to about 1800 – 2000 Watts. However, let’s conservatively assume the starting wattage of the air conditioner’s compressor has been limited to no more than 2500 Watts.
Let’s recalculate the required Peak Wattage of the generator:
Generator’s Peak Wattage > Compressor’s Starting Watts + Running Watts of the other appliances
Generator’s Peak Wattage > Compressor’s Starting Watts + Rridge Watts + TV Watts + Slow Cooker Watts + Lights Watts + Fans’ Watts
Generator’s Peak Wattage > 2500 Watts + 200 Watts + 60 Watts + 200 Watts + 100 Watts + 400 Watts
Generator’s Peak Wattage > 3460 Watts
With this update, we’d be able to use a smaller generator, such as the WEN 56380i, which has a Peak Wattage of 3800 Watts, and a Rated Wattage of 3400 Watts.
To spare you the hassle of identifying the wattage of each of your appliances, I’ve created a convenient generator size calculator.
You can simply make a list of appliances by choosing from the drop-down menu, get an estimate of the running and starting power requirements of each appliance, and then find out the generator size you should consider:
