Lovejoy Coupling FAQ: L090 vs L150, VFD Basics, BLDC Control, Actuator Types

Lovejoy Coupling Questions I Answer Almost Every Week

We get a lot of calls that start with “this is probably a dumb question” and then continue with the exact question I wish every order form asked. I’m a quality/compliance manager at a power transmission distributor. That means I review coupling specs before they reach customers—roughly 1,100 line items a year, give or take. Most of my job is catching the mismatch between what someone wants and what their machine actually needs.

This FAQ covers the questions that show up most around the Lovejoy coupling and the motors we pair with them:

• L090 vs L150 Lovejoy coupling—which frame do I buy?
• What’s a VFD? What does it actually do?
• Does a VFD change coupling selection?
• What does brushless DC motor control require?
• Electric actuator types—what is the real tradeoff?
• Is a bigger Lovejoy coupling safer?
• When a coupling fails, is it a bad part?

1. Lovejoy coupling L090 vs L150—which one do I need?

Short version: both are L-Type jaw couplings—two hubs with an elastomeric spider in compression—but the L150 is a much larger frame. The number is not the bore size. In the Lovejoy catalog, L090 and L150 are hub frame classes. If an order picks one by shaft diameter alone, I send it back for the full spec.

Start with torque. People pick by motor horsepower, but torque is what twists the spider.

Coupling torque (lb-in.) = (motor HP × 5250 ÷ rpm) × 12. Apply the service factor from the catalog before comparing to a coupling rating.

In our stock, an L090 hub is more typical for smaller motor shafts—up to the 1-1/8-in. neighborhood, if my memory of the catalog is right. An L150 hub is heavier and handles larger bores and keyways, with considerably more torque capacity. But I’d have to check hub material and spider durometer before quoting a rating, because both change the numbers.

One audit note: in our Q1 2025 spec review, hub/spider mismatches on Lovejoy product were the largest reason for first-pass rejection on new orders. The parts were fine; the selection process was guessing.

2. What’s a VFD, exactly?

A VFD, or variable frequency drive, converts fixed-voltage, fixed-frequency AC into a variable-voltage, variable-frequency output for a three-phase AC motor. Changing the frequency changes motor speed; changing the voltage keeps the motor current where it should be as frequency changes. That’s the whole trick.

Two things I see overlooked:

One—if you only need on/off at constant speed, a VFD may be overkill. A contactor and overload relay is cheaper, and on some fan and pump jobs it is the right spec.

Two—a VFD is not only a speed control when it runs a standard motor at very low speed for hours. The motor’s shaft fan slows down with the motor, so cooling drops. NEMA MG-1 Part 31 describes inverter-duty motors designed for this; I reference that standard whenever a package includes a VFD and the customer plans sustained low-speed running.

3. Does a VFD change which Lovejoy coupling I choose?

Often not—but sometimes it changes everything. If the VFD just ramps the motor up and runs near nameplate speed, the coupling selection is usually the same as across-the-line start. If you use the drive for frequent starts, fast reversals, torque limiting through a jam, or continuous operation across a wide speed range, treat the coupling duty as heavier, not lighter.

The coupling does not know what a VFD is. It only transmits torque. The question is whether the drive creates torque spikes the original selection never accounted for. I have rejected more than one “this worked on a conveyor” coupling choice for cyclic servo or VFD duty. The spider can handle normal misalignment, but a shock load through a jammed machine will still damage it.

(Should mention: oversizing the VFD does not protect the coupling. Match the drive to the motor FLA, and match the coupling to the peak torque at the load shaft.)

4. What does brushless DC motor control require?

A brushless DC motor is effectively a permanent-magnet synchronous motor. It needs an electronic controller to energize the windings in sequence—usually using Hall sensors, an encoder, or sensorless back-EMF detection. Applying DC power alone will not keep it spinning; it may jerk to one position and stop.

The practical list: a compatible brushless DC controller or servo drive, a motor with the right feedback option, and a supply sized for peak current, not just continuous current. Motor-drive matching matters more than people expect. When someone pairs a random motor with a generic controller and gets commutation faults, the coupling and motor get blamed first. Usually the control loop is the real problem.

On the coupling side, I always check peak torque, not nameplate continuous torque. Brushless motors can deliver several times continuous torque for short bursts. If you size an L090 or L150 Lovejoy coupling to the average torque number, the spider can fail on the first aggressive move.

5. Electric actuator types—what is the real tradeoff?

In the motion systems I review, electric actuators mostly fall into four families:

• Ball screw actuators—good efficiency, higher thrust, better positioning; more expensive and sensitive to side load.
• Lead screw actuators—lower cost, self-locking, simple; lower efficiency and duty limits.
• Belt-driven actuators—fast, long travel, light load; less stiffness and precision at the end of the stroke.
• Direct drive (linear motor or torque motor)—highest speed, precision, and cost; no screw or belt wear, but more engineering.

The mistake is asking which one is strongest. The right question is what the cycle looks like: thrust, speed, duty cycle, repeatability, and budget. A high-thrust 24/7 application usually points to a ball screw; a long-stroke light-indexing job points to a belt; and a very clean high-speed positioning axis might justify a linear motor.

I get involved when the motor connects to the actuator. With screw type actuators, the servo motor is often coupled directly to the screw. That joint must tolerate slight misalignment and axial growth without adding backlash to the position loop. I’ve seen repeatability problems traced back to an oversized rigid coupling that transferred heat and thrust into the motor bearing.

6. Is a bigger Lovejoy coupling safer? Should I oversize?

I hear this weekly: “I’ll take the L150 Lovejoy coupling instead of the L090; better safe than sorry.” It sounds logical, but bigger is not free. Larger hubs add reflected inertia to the motor shaft. On a servo or fast start/stop application, extra inertia reduces effective acceleration and can make the tuning fight you.

Oversizing also changes torsional behavior. The spider in a jaw coupling contributes damping and compliance to the system. If the coupling is so oversized that it barely flexes at normal torque, those small vibrations have nowhere to go but into the gearbox or bearing. And on servo axes, a different compliance means a different tune.

My recommendation is the same one I use on order review: compute torque at operating speed, apply the catalog service factor, confirm the bore and keyway fit, then pick the smallest frame that satisfies all of those. If you want extra margin, that is what the service factor is for. Two sizes up does not prevent failure; it buys a different failure mode.

7. If a Lovejoy coupling fails, is it a bad-quality part?

After several years of inspecting returned couplings, I can tell you this: the visible failure is rarely the root cause. Misalignment beyond the catalog limit, a torque spike, chemical attack on the spider, or a bore/keyway mismatch shows up as a cracked or worn coupling. The failed part looks guilty, but the application was the problem.

The assumption is “coupling failed, therefore coupling quality was bad.” The reality is more often “the wrong coupling was selected or installed and it failed under conditions it was never rated for.” That is not a bad Lovejoy coupling. It is a badly applied Lovejoy coupling—and there is a difference.

I still kick myself for one L090 order in 2023. We confirmed the bore fit but never verified the keyway width. The shaft had a 3/16-in. keyway; the hub was cut for a 1/4-in. key. It cleared the bore and looked right at a glance. The result was rework at our cost, a week of downtime, and a rule change: now every coupling order includes a keyway sign-off before it reaches the queue. The checklist is the cheap insurance. (Mental note: I still owe that maintenance lead the corrected L090 datasheet.)