I keep a list. It started in 2017 as pure frustration — a running tally of every Leeson motor I'd replaced that "died too young." Seven years later, that list has 40-something entries, and I've started to treat it less like a complaint ledger and more like a confession.
Because honestly? Most of those motors weren't the problem. I was.
Here's the uncomfortable truth I learned the hard way: most premature motor failures aren't the motor's fault. They're the application's fault. And the blame usually starts at the order desk.
The Problem I Thought I Had
The typical call went like this: "The Leeson pump motor is burning out. It's seven months old. We need a replacement by Friday."
I'd pull the old motor, order a matching Leeson DC permanent magnet motor, install it, and close the ticket. Then, four to six months later, the same customer called with the same words. "It burned out again."
At first I blamed the parts. "Bad batch." "The new ones aren't built like the old ones." Whatever helped me sleep. But I wasn't sleeping that well, because the failures weren't random — they were consistent.
The First Clue: Every Post-Mortem Looked the Same
When I started pulling end bells off failed motors instead of just swapping them, the story never changed. Varnish discolored from heat. Bearings dry or leaking. Brushes worn unevenly. And that burnt-lacquer smell — I can recognize it instantly now, and I honestly hate it.
I don't have hard data on industry-wide defect rates, but based on the failures I've documented, I'd guess that maybe one in ten was a genuinely bad motor. The other 90%? The motor was doing exactly what it was designed to do. The application was wrong.
My experience skews toward 1/2 to 5 HP motors in pumps, conveyors, and packaging lines. If you're running heavy industrial motors, some of this may not transfer. The physics generally does.
That was humbling. It meant I'd been charging customers to "fix" problems that I was re-creating with every order.
What Was Actually Killing These Motors
Once I got past the nameplate, the real causes sorted into four buckets.
1. Duty cycle: the rating nobody reads
"Continuous duty" means the motor can run indefinitely at rated load. But a lot of Leeson DC permanent magnet motors are not marked continuous duty. They're marked "30 min," "60 min," or "S2" — meaning they're designed to run, get hot, and cool down between cycles.
In 2019, I pulled apart a 30-minute-duty motor that had been running a hydraulic pump skid for 11 months straight. It was in pieces before I even removed it from the skid — the commutator was destroyed. That was my first real lesson in what the old-timers call the 10°C rule: insulation life roughly halves for every 10°C rise above rated temperature. I've seen that rule quoted in EASA materials for years, and it's never been wrong in my experience. Run a short-duty motor on a continuous load, and you aren't shortening its life gradually — you're putting it in a death spiral.
2. Power supply: the quiet killer
DC permanent magnet motors sound simple. They're not. They need clean, regulated DC. I once watched a colleague connect a 90V Leeson DC motor to a nominal 120V line through a simple bridge rectifier — no filtering, no regulation. The motor ran fast and hot, the brushes sparked like a cheap fireworks show, and the motor was scrap in six weeks. "Rectified AC" is not "DC." It's rectified AC. The difference absolutely destroys brush life.
If your brushes are dying fast and the motor runs hotter than expected, check the power supply first. In my experience, that's the culprit more often than the motor itself.
3. Technology mismatch: the stepper motor confusion
This is where things get interesting — and, to be fair to myself, more recent. As small automation spread through shops, the question "what stepper motor should I use?" started showing up in our inbox instead of "which Leeson motor?"
Here's the thing: a stepper motor is not just a fancier DC motor. It moves in precise angular increments, holds position when energized, and handles positioning work that a plain DC motor can't do on its own. I've argued with customers who insisted they "just needed a motor" for an indexing table when they really needed a stepper or a servo.
I went back and forth on that exact call for a week. The numbers said a stepper with a quality driver would be enough. My gut said the servo was safer because the customer had no idea how to tune anything. Turns out my gut was right — but a stepper with an encoder did the job in the end, and I had to rebuild the machine's control scheme twice. If the application needs position holding, it's a position application. Buy for the physics, not the price.
That said, if you need continuous variable speed, a Leeson DC permanent magnet motor is still a legitimate choice. The point is picking the right class of motor for the motion profile — not just searching for whatever's in stock.
4. Rotary vs. linear: picking the wrong geometry
The other mistake I keep running into is choosing the wrong motion geometry. A customer once told me they needed "an electric actuator, rotary type." After two rounds of emails, it turned out they basically needed to push a gate valve straight down. That's not a rotary application at all. It's linear.
I've made this mistake myself. Late in 2022, I cobbled together a rotary electric actuator with a screw assembly to convert rotation into linear motion, just to use stock parts. It worked for about three weeks. Then the thrust bearing let go, and we had a gate stuck under pressure. Customer patience went with it.
Bottom line: if the motion is straight, buy a linear actuator motor. If the motion is rotational, buy a rotary actuator or a gearmotor. Don't patch a rotary into linear service unless you truly understand the thrust loads.
The Real Cost: It's Never the Motor That's Expensive
A $400 Leeson motor fails. You order a replacement, pay expedited freight — $90. You pay someone $85 an hour to swap it — two hours minimum. The machine's down for a week, so you lose production. The motor is maybe 20% of the true cost. And that's on a good day.
My single biggest mistake was a 12-unit order for a packaging line in 2019. I specified a Leeson DC permanent magnet motor that looked perfect on paper: right voltage, right speed, right shaft. But I'd missed the insulation class requirement and the actual ambient temperature next to the oven line. Those motors cooked themselves in four to five months. Replacement parts ran about $3,200. Labor and downtime added another $4,000 or so. And I had to call the plant manager and admit I'd violated my own notes.
That call changed how I work. I put a small copy of NEMA MG 1 on my desk and started reading nameplates like they were brake tags.
What I Actually Do Now
No magic formula. A boring checklist. But it's caught 47 potential errors in the past 18 months, and it's stopped me from ordering the wrong motor more times than any engineering instinct I own.
- Read the whole nameplate. Duty rating, insulation class, ambient temperature allowance, enclosure type. Per NEMA MG 1, insulation class is a thermal budget — Class F, for instance, allows 155°C total temperature. That includes ambient plus winding rise plus hot-spot allowance. In a hot plant, you've already burned through a third of that before the motor turns an inch.
- Ask about the environment. Heat sources, debris, washdown procedures. "The motor isn't a submarine" is a sentence I've said far too many times.
- Confirm the technology. Positioning? Stepper. Variable speed with controlled acceleration? DC permanent magnet motor with a proper drive. Straight-line movement? Linear actuator motor. Rotation? Rotary actuator or gearmotor.
- Measure the power supply. Proper DC drive? Voltage stable under load? Five minutes of measuring has prevented at least a dozen repeat failures — and I used to skip it every single time.
Bottom Line
What was considered solid motor selection practice five years ago is getting harder to hold onto, not easier. Online listings strip context. Buyers type "what stepper motor" and end up clicking "buy" on a DC motor because the price was low. It's a mess out there.
But the fundamentals haven't changed. Duty cycle, thermal limits, power quality, and application fit — those still decide whether your Leeson motor sees ten years or ten months.
I still kick myself for the money I wasted replacing motors that probably deserved a longer life. If you've got a "burning out" motor on your floor, don't replace it yet. Post-mortem it first. Somewhere in that burnt smell is a lesson, and it's a lot cheaper to learn it from my list than from your own.
These days, there's a particular satisfaction in pulling a motor and finding clean, healthy windings. It means the checklist worked. After 40+ replacements that never should have happened, I'll take that small win.
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