Motors aren’t everlasting implements, and no motor lives forever. According to Acorn Industrial Services Ltd., most electric motors have a life expectancy of anywhere from 30,000 to 40,000 operating hours. But that estimation depends on a number of factors. Is the motor properly secured and any vibrations minimized? Are workplaces kept clean in order to minimize contamination from dirt and grime? And is your motor supplied with high-quality energy?
That last query might sound a little strange to some. Power is power is power — right? Not exactly. In this post, we will explain the relationship between voltage, amperage, and horsepower, as well as how they can affect the longevity of your pump.
What Determines a Motor’s Horsepower?
During the 18th century, Scottish practical scientist James Watt developed a way to measure a single unit of power. Watt’s concern was steam engines, but his mathematical formula ended up focusing on something else entirely: the humble draft horse. He calculated a single unit of power (i.e., one horsepower), by having a draft horse lift a 550-pound weight one foot in one second. In formula form, it looks like this:
Horsepower = Work / Time
In the case of the horse moving its weight, work equals force times distance.
Though horsepower is a basic measurement, it can be applied in a number of different ways depending on the use case. We can see this, for example, when pumping fluids. In such a scenario, work will equal:
Horsepower = Vertical feet traveled * Flow Rate in Gallons Per Minute * Specific Gravity of the Fluid) / 3960
In this equation, gallons per minute per foot takes the place of time and equals 3960. If any of the variables change, such as the flow rate, feet traveled, or fluid viscosity, the horsepower required will also change.
When we examine the motors that power pumps in isolation, we see two further ways of determining horsepower. Mechanical horsepower alters the formula to read:
Horsepower = (Torque * Revolutions Per Minute) / 63,025
Electrical horsepower is far simpler to calculate. See, horsepower can also be measured in James’ eponymously named watts, with one horsepower equaling 745.699872 watts. (Electrical applications generally round to 746 watts.) It’s easy to convert one to another, and this relationship will play an important role in our next section.
How Voltage Impacts Motor Output and Speed
We all know that the watt is related to electricity and that it’s also a measure of power. However, it’s far from the only important metric when measuring electricity. You also should pay attention to:
- Amps (a measure of the current flowing through a circuit)
- Ohms (aka, resistance or the maximum amount of electricity that can flow through a circuit, which decreases as elements are added to the circuit)
Watts have a direct relationship with volts, which can be expressed by the following mathematical formula:
Watts = Voltage * Amps
As long as a motor’s torque (i.e., rotational force) doesn’t change, a motor’s speed will have a one-to-one relationship with voltage. If the voltage falls, the motor’s speed will decrease by the same amount. The opposite also holds true if voltage increases.
Effect of Low Voltage Supply
However, voltage is simply a single element in play when it comes to supplying power to a motor. Amperage (i.e., resistance) is a key part of the equation. So is current, although you won’t see it in the formula.
To put it simply, current describes the way in which electricity is delivered. A battery will deliver steady direct current (DC). Power from a plant, though, is delivered as alternating current (AC), which you can think of as a sine wave that oscillates above and below some median amount of voltage. Low-quality current may have extreme variations, which can cause issues, as we will see.
Once you understand the relationship between these factors, you can begin to see the problems of low voltage supply: It alters the amps and current used by a motor, which can have unintended consequences.
What Causes a Motor to Draw Higher Amps?
Motors require a certain output in watts in order to function, and this is the result of a voltage multiplied by amps. So when voltage falls, resistance scales up in order to supply the difference, and the motor will also draw more current. Now, some variation is expected given the nature of alternating current. Motor manufacturers even produce nameplate ratings showing the maximum amount of current that the device can draw. But when voltage drops too low (or, as we’ll see in a moment, gets too high), amps and current draw can spike.
What Happens if the Amps are Too High?
When amps get too high — which usually has a concomitant excess current draw — several things happen. These may include:
- A spike in temperature that lowers the economic life of the motor
- A decrease in operating efficiency
- Reduced starting ability
- Eventual unscheduled shutdowns due to pump failure
Interestingly, an increase in voltage beyond typical operating parameters can also lead to similarly negative results. Why? Well, when voltage gets too high, it tends to disrupt the magnetic portion of a motor. The motor then begins to pull additional current in an attempt to remagnetize itself. The results are largely the same as when voltage is too low.
In addition to having more than six decades of experience in creating innovative pump systems (which include motors!), March Pumps also has the know how to help design, install, and operate one for you. Contact us! Your gain is our goal.