Hey everyone, it’s Jake here, and if you’re in the market for or already working with Spur Gear Motor units, you’ve probably run into power factor issues at some point. I get it—power factor isn’t the most glamorous topic, but if your motor’s power factor is low, it’s costing you money in energy bills, potentially shortening your motor’s lifespan, and even running the risk of utility penalties. As someone who’s been a spur gear motor supplier for over 8 years, I’ve seen all kinds of headaches from bad power factor, and today I’m breaking down exactly how to fix it—no stuffy engineering jargon, just practical, actionable steps that work.
First, let’s keep this super simple: power factor is basically a measure of how effectively your motor uses the electricity it draws. It’s a ratio between real power (the actual work your motor does, measured in watts) and apparent power (the total power pulled from the grid, measured in volt-amperes). A perfect power factor is 1.0, which means 100% of the electricity is turning into work. Most spur gear motors, especially smaller DC models like the 12V DC Gear Motor, sit between 0.6 and 0.85 on average—and if you’re below 0.7, that’s where the real costs start hitting. I once had a customer who ran 20 of our Low Rpm Electric Motor units in their conveyor line with a 0.62 power factor; they were overpaying $1,200 a year in wasted energy, just because of that small gap.
So why do spur gear motors have low power factor in the first place? The main culprits are inductive loads from the motor’s windings, underloaded motors, and outdated components. Let’s go through each fix one by one, starting with the easiest wins that require no big hardware changes.
First up: stop underloading your motor. This is the #1 mistake I see new customers make. A lot of folks buy a spur gear motor that’s “bigger than they need” just to play it safe, but if your motor’s only running at 25-50% of its rated load, its power factor drops like a rock. Motors are most efficient (and have the highest power factor) when they’re running at 75-100% of their rated load. Think about it: a motor built for 100W of work doesn’t use electricity as efficiently when it’s only doing 20W of work—it’s spinning its windings idle, wasting power as heat. I had a bakery customer last year who was using a 2HP spur gear motor to drive a small mixer that only needed 0.5HP. We swapped it for a properly sized 0.75HP unit, and their power factor jumped from 0.61 to 0.82 overnight. That’s a 34% improvement with zero new parts, just a size check.
But what if you can’t swap the motor right away? Maybe you have a fixed setup that doesn’t let you adjust load easily. Next fix: add power factor correction (PFC) capacitors. These are small, relatively cheap components that counteract the inductive lag from the motor’s windings. Inductive loads (like motor coils) pull current that’s out of sync with voltage, which is what lowers power factor. Capacitors create a “leading” current that cancels out that lag, bringing the ratio closer to 1.0. Here’s the thing—you can’t just buy any capacitor and stick it on. You have to calculate the right size for your motor’s rated power and existing power factor. If you oversize the capacitor, you’ll actually make the power factor go lagging or even leading, which is just as bad. The good news is most local electrical contractors can do this calculation for you for under $100, and the capacitor itself costs $50-$150 depending on the motor size. I’ve seen customers recoup that cost in 6-12 months from energy savings.
Wait, but does this work for DC motors? A lot of people ask me that, because the PFC talk usually focuses on AC. But for brushless DC spur gear motors (which are the most common modern models), internal PFC is already standard on most units like our 12V DC Gear Motor line. If you have an older brushed DC motor, external PFC caps still work—just make sure they’re rated for DC voltage and matched to your motor’s current draw. I always tell folks, when you’re shopping for a new spur gear motor, double-check if it has built-in PFC. That small feature can boost power factor by 0.15-0.2 right out of the box, no extra work needed.
Next, check your motor’s winding connections. This is a free fix, takes 10 minutes, and I can’t believe how many people skip it. Over time, as a motor ages, wiring can loosen or corrode, or someone might have misconnected the windings during installation. For AC spur gear motors, wrong winding connections can make the motor run at a lower voltage than it’s rated for, which kills power factor. For DC models, loose wiring increases resistance, making the motor work harder to get the same torque, dragging power factor down. Last month, a customer of ours had a Low Rpm Electric Motor that was performing weirdly—slow, hot, and power factor was 0.58. We sent a technician out (on our dime, since he was a repeat customer) and found that the main power wire was corroded at the terminal block. After cleaning and re-securing the connection, power factor jumped to 0.79. No parts, no cost, just 10 minutes of work. Moral of the story: periodically check your motor’s wiring, especially if it’s in a dusty or humid environment.
Another underrated fix: upgrade your motor’s bearings and lubrication. If your spur gear motor’s bearings are worn out, it’s putting extra strain on the motor’s shaft, which makes the windings draw more current to overcome that friction. More current = lower power factor. I’ve seen this happen with motors that run 24/7 in factories—after 3-5 years, the grease dries up, and bearings start to wear, creating that extra drag. A friend who runs a packaging plant told me they had 12 spur gear motors running their sorting line with an average power factor of 0.68. They did a full bearing replacement and regrease on all of them, and within a week, the average jumped to 0.81. The total cost was $450 for parts and labor, and they saved over $900 a year in energy. That’s a quick win with a big ROI.
Wait, what about variable frequency drives (VFDs)? A lot of people use VFDs to control motor speed, and some VFDs actually improve power factor. But hold up—you have to get the right VFD for your setup. If you get a cheap, unfiltered VFD, it can actually create harmonic distortion, which messes up power factor more than it helps. Look for VFDs with active PFC (APFC) built in—those adjust the current waveform to match voltage, keeping power factor high even when the motor is running at partial speed. I recommend talking to your electrician about sizing the VFD to your motor, not just to the speed you need. For example, if you have a 2HP spur gear motor, don’t grab a 5HP VFD “just in case”—that’s overkill and can lead to lower power factor.
Now, let’s talk about when it’s time to replace your motor instead of fixing it. If your current spur gear motor is over 10 years old, has a power factor below 0.65, and you’ve already done all the fixes above, it’s probably more cost-effective to swap it out for a modern, energy-efficient model. Our Spur Gear Motor line is all built with internal PFC, high-efficiency windings, and sealed bearings to keep power factor above 0.85 even at 75% load. We did a test with our 12V DC gear motor last quarter—ran it at 60% load (which is a common underload scenario for many small applications) and still got a 0.83 power factor, compared to an old competitor’s model that only hit 0.59 at the same load. That’s the kind of difference that adds up over thousands of operating hours.
I also want to bust a common myth here: power factor is only a big deal for big industrial motors. Nope, even small motors like our 12V DC gear motors used in robotics, vending machines, or small conveyors can have low power factor that adds up. If you have 10 small motors all with a 0.65 power factor, that’s the same wasted energy as one big motor with a bad power factor. So even if you’re a small business owner with a few spur gear motors, this stuff matters for your monthly electric bill.
Let’s recap the quick checklist to improve your spur gear motor’s power factor, so you don’t have to remember all this:
- Make sure your motor is sized correctly for your load (75-100% rated load is sweet spot)
- Check and tighten wiring connections, clean corrosion if needed
- Add PFC capacitors if you have AC motors, or go for built-in PFC when buying new
- Service bearings and lubricate if they’re worn or dry
- If using a VFD, pick one with active PFC and proper sizing
Now, if you’re reading this and thinking “my current motor’s power factor is too low, and I need help figuring out the best fix”—that’s what I’m here for. As a spur gear motor supplier, I don’t just sell motors, I help customers get the best performance out of them, including power factor optimization. Whether you need to swap out an old unit for a new high-efficiency model like our Low Rpm Electric Motor line, or need help calculating PFC capacitor sizes, or just have questions about how to adjust your current setup, I’m happy to chat.
I’ve worked with everyone from hobbyists building custom robots to large manufacturing plants, and every time we fix the power factor issue, the customer sees real cost savings within months. Power factor doesn’t have to be complicated, and you don’t have to be an engineer to make small changes that make a big difference.
If you’re ready to improve your spur gear motor’s power factor, or want to learn more about our line of high-efficiency, high-power-factor motors, reach out to our team to talk through your specific application. We’re here to help, not just sell you a product.
References:
- Electrical Contractor Magazine. “Power Factor Correction for Small Motors.” 2022.
- National Electrical Manufacturers Association (NEMA). “Motor Power Factor Best Practices for Industrial Applications.” 2021.
- US Department of Energy. “ Improving Motor System Efficiency: Power Factor and Motor Sizing.” 2023.
- IEEE Transactions on Industrial Electronics. “Efficiency and Power Factor Optimization for DC Gear Motors.” 2020.
