Any generator, whether it uses gasoline or propane, is going to have two power ratings. Most of the manufacturers mention only one from the two, and it generally is the starting watts. If you take a deeper look at generator specifications, then you will discover that there is also running watts other than starting watts.
To properly understand the terms, you will first need to have a basic understanding of what does power and work mean.
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Work and Power
Let’s start with power. We can define power as, in simple terms, the ability of equipment or a person to do a certain amount of work at a certain time. If the work can be done in less time, then the power will be more compared to when more time is taken to complete the same work.
That means the power is a measure of the rate of work done.
With this thing understood, we can put it into an equation like this :
P = W/t
Where “W” is work and “t” is the time taken to do the work.
Now work, you can vaguely define the work as an effort. In general physics, you may have studied, a general definition of work is if you move an object from one place to another covering the distance “d,” and the force exerted on the object is ”F” then you can put it like this :
W = F*d
Where “W” is work done, “F” is the force with which the object is moved, and “d” is the distance up to which the object has traveled.
As the work can be seen as an effort, but you can’t quantify the effort, that’s why we have defined the power, which associates time with the effort. This association gives the idea about the ability of a machine or person to do the work.
Similarly, a generator does the work to keep supplying the power, but that work will be of a mechanical nature. It uses the energy of the fuel to run the engine, which in turn generates the electricity and due to this work you get the power at the terminals.
That power is a relation between the voltage at the terminal and the current flowing out of that terminal. That relation is the wattage of the generator. This power is due to the motion of the engine, which runs the motor, and the voltage and the currents are generated, so the mechanical power is converted into electrical power and is denoted as P.
Power P for the generator is defined as:
P = V*I
Where V is terminal voltage, and I is terminal current. The unit of this power is the watt. To get a feel of that unit, know it like this, a watt is a unit to describe the rate of energy generated. The terminal means the output ports.
Starting Watts and Running Watts
Some house appliances will have two power ratings; the high power they need only for a few seconds at the starting phase is known as starting watts. Afterward, to work continuously, the power they need is known as the running watts.
Small appliances like bulbs, toasters, and TVs don’t have the starting watts, or they don’t need more power than the running watts to start. On the other hand, the refrigerator, fans, and the air conditioner (mostly inductive loads) in the house will have starting watts. This is because they have a motor incorporated into their system, which needs more power to start rotating at the desired speed.
The energy needed to achieve a certain speed from a steady condition is going to be more compared to keeping it rotating at that speed.
Generally, the starting power needed for the motor to start at a certain speed will be 3 to 5 times higher than the power needed to maintain that speed. But the fact is, the generator supplies constant voltage, so from the definition of power, you can see that the current will be higher at the starting.
It is the high current that the generator needs to supply to the loads at the starting for a few seconds without sustaining any damage to itself. Even though this current will be for a few seconds only, but if any load draws the large current for more than a few seconds, the generator is equipped with a circuit breaker.
The circuit breaker will trip if it detects the higher current, which is sustained for more than a certain period. So, your generator will be safe from overload.
On the other hand, the running watts is the rating that a generator can continuously supply without any trouble. This rating is lower than the starting watts. Running watts is the power that any equipment will need continuously to keep working.
How to Choose the Generator Rating?
When selecting a generator, the consideration of the running watts and the starting watts is of utmost importance.
To know the output rating of a generator, you will need to consider the running watts of all the appliances that you are going to use simultaneously and add them up. This is the wattage your generator must supply continuously.
For small appliances, you might run into a problem finding the wattage rating, but for the large appliances, it will be given on the label.
The wattage is nothing but the multiplication of the voltage and the current, so to get the wattage for small appliances, you can multiply voltage and current ratings.
That was the calculation for the running watts, now coming to the starting watts, find the appliance with the largest starting watts required. That will be the starting watt rating of the generator.
There will be some appliances, based on the generator’s rating, you will be able to run them but can’t start them. For example, a central air conditioner of 3 tons has 5400 running watts and 7200 starting watts. If the generator has a rating of 7000 starting watts and 6000 running watts, then the air conditioner won’t start, but if started, the generator can run it satisfactorily.
Furthermore, make sure that if you are going to start two or more appliances with the starting watts, because you will need to add starting watts of those appliances, and that will be the final starting watts that your generator should supply.
It will be very helpful if you get the generator with a rating of 20% more than the actual need, so it will allow you to do the expansion if required in the future. Moreover, if the generator runs at 20% less than its capacity, you get the most out of your generator, longer lifetime, better fuel economy, etc.
For a safe operation, a good practice is to start the appliances with the highest rating first and then attach other appliances.
Final Thoughts
Now, with this discussion, you know what you need to do to select the rating of the generator, and you know what starting watts and running watts is and their importance.
So, when inspecting any generators, don’t limit yourself just to one rating and inquire about the others as well. If you can’t find the one that can satisfy your power calculation from one brand, then jump to another. After all, you don’t want to end up with a generator that can’t start a few appliances when you need them to.
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Thanks Evans for taking the time to share your knowledge!