## Selecting and Sizing a Solenoid for Linear Motion

May 5, 2022

Design and application engineering both require balance. Most engineering challenges are complex.  Rarely do they involve only one variable or mutual exclusivity between variables. Increase size here and lose some over there. More power means more heat. Faster actuation often leads to higher impulse loading and more wear. The list goes on. Carefully tracing down the contours of a multi-variable manifold is the engineer’s bread and butter. Sizing a solenoid is no different. To prove this, let’s walk through sizing and selecting a solenoid for a fun – yet desperately needed – application:

The Application: a breakroom de-scentsitizer:

You’re a diligent engineer. Sometimes you stay late. Sometimes you come in early. You do whatever it takes, even working through lunch. You head to the breakroom shortly after the lunch rush, just after that last bowl of leftovers has left the lunchroom. You have, through no fault of your own, become very familiar with what happens when you mix the smell of burnt popcorn with chicken alfredo and last night’s Thai food and everyone else’s lunch smells. It isn’t pretty! You and your nose wade through that battlefield every day on your way to the refrigerator. And, what’s worse, short of parking an industrial grade kitchen exhaust hood above that microwave, turning the fan speed dial past 10 to typhoon, there really isn’t much you can do.

Or is there?

What if you had a small device, about the size of a soap dispenser, that you could mount somewhere just outside the microwave? What if this little device sprayed food-safe, odor neutralizing spray, eliminating the odor right at its source? Voila!  Problem solved! Right? What if you interlocked it with the microwave door? You could use a solenoid to actuate an aerosol can every time the door interlock closed, and just like that you never have to smell your coworker’s broccoli chicken alfredo again.

It can’t be that easy, can it? It can!  Let’s walk through how to size the solenoid for this application.

It’s tempting to throw in a tl:dr for the zoomers, so here’s that:

TL:DR How to Size a Solenoid.

• Measure necessary force and stroke to actuate your mechanism
• Define the duty cycle of your application.
• Calculate necessary electrical power input and define supply voltage.
• Use solenoid data to find a solenoid that meets force requirements at stroke.
• Pick a suitable coil gauge given your supply voltage.
• Implement a return mechanism and solve whatever other various application-specific problems (vertical orientation, timer circuitry to prevent repeat actuation, etc.)

## Sizing a Solenoid (via basic Energy Balance):

A solenoid is, in its most basic sense, an electromechanical device that receives electrical energy as input to pull the ferromagnetic iron plunger into the coil of wire and do work on some mechanism – in this case, the top of the aerosol can. (If the magic of electromagnetism is still astonishing to you and even if you know Maxwell’s equations like you know your ABCs, you still might enjoy the Feynman Lectures https://feynmanlectures.caltech.edu/II_toc.html).

The first step in sizing a solenoid for an application is to figure out how much mechanical energy is required for motion of the mechanism (aerosol can). As you know:

$W=Fd$

Where, W is work, F is force, and d is distance.

Measure the total travel of the plunger shaft, starting just above the top of the can button and ending the distance the button has traveled after a puff of the appropriate size is dispensed. It’s about 3⁄8 “. You happen to have a mass weighing 1lb and if you set it on top of the can it compresses it without damage. So, you need a 3⁄8 ” stroke length and a force of 1lb.

For the electrical side, a simple energy balance:

$W=Fd=ηIVt$

Where η is an efficiency factor, I is current, V is supplied voltage, and t is actuation time.

You would like to supply a voltage no greater than 12V, which might seem a bit high, but as we’ll see later, a stroke of 3⁄8 ” precludes lower voltages (at least without also using capacitive discharge or a coil with a low gauge, both effectively increase supply current to solenoid).  We ballpark an electrical efficiency factor of 0.1, which is fairly inefficient. Solenoids, while being a practical means to convert electrical energy into mechanical work, are also very effective heaters.

As a result of $I^2 R$ losses and the relatively low efficiency of a solenoid, heat generation is one of the primary concerns. Therefore, it’s important to consider the duty cycle of the solenoid; which is defined as a ratio of the period during which power is supplied over total time of a cycle. Like this:

In this case, we only want the solenoid to actuate long enough to dispense a single puff, so let’s say our solenoid should be on for no longer than 100ms and be off for at least 300ms. This gives a duty cycle of 25%.

As an aside, to affect this kind of duty cycle in some applications where the user is allowed to repeatedly switch on power to the solenoid, it may be necessary to implement timer circuitry to prevent this kind of repeated actuation. For simplicity’s sake, let’s assume that no one will need more than one puff and that all our users are fairly well-behaved (where this is obviously a very rough assumption because we all know that some food smells more than others. This can be both good and bad. I’m looking at you Mr. I-didn’t-mean-to-leave-the-popcorn-in-there-for-that-long).

Next, evaluate the earlier energy balance equations. From a force perspective, in SI units:

$W=Fd=(4.4N)(.0095m)= .0418J$

Now, solve the electrical half of this equation for the power term:

The calculation tells us that we need a solenoid with 41 watts of input power to generate the desired force at stroke.

### Force/Stroke Graphs:

Now we need data on how much force a solenoid can produce at a particular stroke and input power. Using the JE catalog as an example, you’ll see the STA Tubular line is organized by size (diameter x length) from ½”x½” up to 1 ½”x 2 ½” and separated into both push and pull models.  We need a push for our application. The force vs stroke and actuation speed graphs can be used for a first pass selection. Note that force decreases exponentially with increasing stroke and that strokes longer than 2” are difficult for a solenoid. We need a stroke of 3⁄8 “. The force/stroke graphs, show four curves that represent the force/stroke profiles of the solenoid at a particular duty cycle. Here’s an example:

A quick word on the relationship between force, current and duty cycle. A solenoid’s force (at a given stroke) is roughly proportional to the square of its amp-turns.  An amp-turn is a unit derived from the number of times the wire is wound around the bobbin multiplied by the current supplied to the coil. For a given coil, holding the number of turns constant and the geometry of the coil (i.e., diameter, length, cross sectional area), an increase in power will increase the force generated by the solenoid. But as mentioned earlier, the heat generated in the solenoid increases with the square of the current. So we find ourselves with a bit of a balancing act. Current, force, and heat are all directly proportional with different ratios of proportionality.  Force goes like the square of a coil’s amp-turns. Heat varies with the square of current. Increase any one of these variables and the others must increase along with it.

Along with the force/stroke graphs are tables separated into four columns by duty cycle. So, too, are the four curves on the force/stroke graphs. These are divided into families of curves ordered by duty cycle or input power. This family of curves is not a discrete set but is continuous as a function of input power. The more power is supplied to the solenoid, the more force is developed at stroke.  However, doing this requires a trade off time-on to prevent thermal damage.

For example, if we select a coil rated for 10W at 4.4 volts and instead give it 8V we may encounter thermal failure like melted coil bobbin or fusing of magnet wire if we keep it powered for an equivalent amount of time.

Back to our selection. Having established a 25% duty cycle with an input power of about 40W, we look through the force/stroke curves to find that the 1”x2” 100-STA (part number: 195207-XXX) is a good fit (see force/stroke graph above and coil gauge chart below for the 100-STA). It’s a good fit from a force/stroke perspective: it generates about 2lbs of force at 25% duty.  And it’s a good fit from a power input perspective, with a 25% duty cycle rated at 40W. The 102-STA would also be a reasonable selection, but it generates almost exactly 1lb of force at stroke, leaving no factor of safety (remember the 102-STA is smaller than the 100). Note that if in application, our duty cycle is lower than 25% then the 102-STA might be a good choice.

## Sizing Coil Gauge:

Almost done! After selecting the 100-STA, we need to select a coil gauge based on the input voltage constraint. We previously decided upon supply voltage of no greater than 12V.  The table above shows that the 23-gauge coil requires 8.9V to generate the 40W needed to provide 1lb force at stroke.  We’ve arrived at the 100-STA with a flat face plunger and a 23-gauge coil (part number 195207-123). Note that if we went with the 60° conical plunger, we might be able to do 20W input power instead and this sort of insight is something engineers are familiar with and the reason why iterative design is so important.

This design envisions the solenoid mounted vertically with shaft down, so something to keep the plunger in place against gravity is needed. The plunger also needs to return to its original position after actuation. A return spring can solve both problems.

We also see that the extra force we sized into the solenoid (2lbs at 25% duty, 1lb over what is actually needed) can be used in part to overcome the spring force during actuation. Return springs are commonly seen in solenoid applications. NB: Recall that the spring force varies linearly with stroke and the force developed by the solenoid varies nonlinearly with stroke. This is a complicated way of saying that at longer strokes you might run into situations where the spring force is greater than the force developed by the solenoid, but at shorter strokes this is rarely an issue.

Since our crash course is becoming more of a slow burn, we’ll assume that we can pick a return spring force low enough that the extra 1lb force will be enough to overcome the linear spring force (a fair assumption).

## In Summary:

Let’s revisit the steps we’ve taken to select our solenoid (TL:DR):

• Measure necessary force and stroke to actuate your mechanism
• Define the duty cycle of your application.
• Calculate necessary electrical power input and define supply voltage.
• Use JE solenoid catalog to find a solenoid that meets force requirements at stroke.
• Pick a suitable coil gauge given your supply voltage.
• Implement a return mechanism and solve other application-specific problems: vertical orientation, timer circuitry to prevent repeat actuation, etc.

While this was a fun exercise for those of us that do this every day, if you find yourself scratching your head and wondering where to start, remember: You do not have to do all this on your own. Johnson Electric employs Application Engineers that will help choose the right solenoid for your specific design – and we’ll have fun doing it!

## MODEX: Are Dark Warehouses the Future?

April 11, 2022

After a two-year hiatus, MODEX was back and bigger than ever. From the very first step onto the show floor, the emerging story was clear. Automation. This material handling industry show looked more like a robotics and automation show. Distribution, warehousing, and fulfillment are undergoing monumental changes in response to the recent events with which we’re all too familiar: labor shortages, rapid e-com growth, and supply chain disruptions. Companies are looking for ways to be more efficient, more responsive, and more flexible. And with this explosive growth in automation, the big question on everyone’s mind seems to be: Are we on the path to a completely dark warehouse?

The global warehouse automation market is forecasted to double over 5 years, from US$29.6 billion in 2020 to US$69 billion by 2025 (MMH). It’s also quite telling – and very evident at the show – that warehouse automation is no longer seen as merely ancillary to industry. Still, it has itself become an autonomous sector independent of its ties to industry/production more broadly. Yet, even this shift in perspective is incommensurate with the impact this growth will bring about both endemically within the warehouse automation space and in our daily lives.

Naturally, growth in automation means more robots. But the definition of robots is expanding from highly anthropomorphic robots in movies like Star Wars’ C3PO to today’s highly automated mobile shelving units. Engineers in this space seek to facilitate processes, and every part of the warehouse is fair game. For example, in the emerging automated micro fulfillment segment, we saw a conveyance system that sent ordered items up to a shelf. Small carts on tracks then sort the goods into their respective cubbies. These self-stocking shelving units are enabling the decentralization and automation of grocery micro-fulfillment.

Growth in automation also means software and data. Software development is enabling bigger and more complex automation. It’s also creating integration between, which until now have been, disparate systems in the warehouse. Where humans were needed to connect the gaps between robots, multi-system integration is now bridging the gap. Big data and AI are the keys to the dark warehouse of the future.

So what does all this mean for motion sub-system suppliers like us? Enabling customers to bridge the gap between traditional electromechanical systems and AI-driven systems of the future with intelligent interconnected motion solutions. Creating smart actuation solutions that provide data on system characteristics enables users to monitor environmental conditions, predictively monitor system health, schedule planned maintenance, and maximize performance. All this, is within the existing motion topology required of your system.

Continued innovation can only be enhanced through supplier partnerships. Sub-system suppliers have robust engineering capabilities and extensive application knowledge to help you achieve your product development goals. If you haven’t connected with your suppliers’ engineering departments, now’s a perfect time.

Dark warehouses most certainly are in our future. How quickly we get there is up to us.

## Partnership is Key in Mitigating Inflationary Price Increases

February 28, 2022

The US ended 2021 with decades high inflation. The pandemic, and the actions taken to contain it, have led to a perfect storm that impacted every aspect of our lives – from personal to professional.

We, at Johnson Electric, much like most of our manufacturing counterparts, have battled production shutdowns, labor shortages, rising wages, commodity price increases and shortages, supply chain issues and surging energy costs. In our day-to-day operations, two components stand out as the main drivers of inflation in our business:

### Raw Materials

Copper and steel are the core components in the products we make, and both have nearly doubled in the last year and a half. Copper rose 93% from $5,050 in April 2020 to$9,765 in November 2021. Steel is up 85% from $560 in April 2020 to$1,035 in October 2021.

### Direct Labor

The Washington Post recently wrote that “manufacturing has weathered the biggest surge in workers quitting — a nearly 60 percent jump compared with pre-pandemic. No other industry has seen an increase like that”. For a long time, manufacturing has offered a path to the middle-class lifestyle in American society and yet people’s aspirations are shifting away from these jobs. According to a 2020 Nielsen study, about 54% of Gen Z indicated they wanted to start their own company.

The intersection of these two trends has made it increasingly difficult to recruit and retain factory workers. We have felt this acutely. To maintain operations, we significantly increased hourly wages, offered free medical coverage and other benefits/bonuses to retain and attract talent.

In the past, we were able to offset increasing costs through continuous improvement activities. However, the historically high inflation is outpacing these activities.

### So how can we compensate for this inflation?

The truth is that, in the short term, we can’t. We are forced to share this inflationary burden with our customers in order to remain solvent. However, we are taking a different approach than in the past. Rather than instituting a general, across-the-board increase, we have deployed an individualized product approach – down to the part number level – taking into account the content of raw material and direct labor. We believe this is a better approach because it leads to meaningful discussions with our customers. Together, we can review the product to identify an alternate or work to modify the design to reduce material and/or labor requirements. This approach also helps us prioritize such activities, together with our customers, based on the largest potential savings.

In the long term, we are automating our manufacturing lines to reduce overall costs and lessen the impact of a fluctuating workforce. This will put us in a better position to protect prices in future inflationary scenarios.

We are actively working with many customers and prospects to optimize costs in new and innovative ways. And we encourage you to reach out to us with your challenges. We are ready to partner with you as we all weather this inflationary storm.

Sincerely,

Vincent Sallé
Vice President
Industry Products Group

## Solenoids in Security Locking Mechanisms

October 27, 2021

A look at modern, technology-driven, security-focused locking mechanisms using solenoids

Security is critical in every aspect of our lives… from protecting personal valuables, important documents, and sensitive paperwork to the way we enter buildings, withdraw money and even open our garage doors. As our technology progresses, so do the ways in which we enhance security all around us.

Many businesses are still using old-fashioned lock and key systems as their primary security measure. However, the industry and security system installers are moving toward electronic locking mechanisms.

With an access control system, the swipe of a badge or a keyfob tap gives people access to their businesses; this happens without ever sticking a key into a lock. These systems are more secure than the traditional lock and key and more reliable than digital keypads and codes.

Whether you scan an ID badge or swipe a keyfob, there’s one thing all access control systems have in common. The security turnstiles, maglocks, doors, and other electronic locking mechanisms that protect us and our businesses require the use of actuation devices.

A solenoid locking mechanism is one of the most effective ways to protect employees and businesses; from security breaches, break-ins, and other security issues.

Most security programs utilize programmed credential devices. Each device has a personal identification number assigned to each individual; these can be programmed to allow or disallow entry at any time. Since the building is only accessible with RFID badges, it’s much more difficult for terminated employees to enter their building; their keyfob would no longer be activated.

In addition to the obvious advantages over the old-fashioned lock and key systems, a solenoid lock has greater design flexibility and enhances security for businesses and personnel.

### Enhanced security

With the frequency of people entering and exiting hospitals, government offices, schools, and venues, security is increasingly a top concern.

With an access control system, businesses can grant clearance to certain parts of the building only to specific individuals. They can also use added sensors in lock assemblies to detect the positioning of the door latch; this ensures security breaches remain at a minimum, with no doors left ajar or alert security to any malfunctions.

With solenoids as the main driver for your system, the lock can be decoupled from the actuation device. This provides added G-Force resistance, so that the locks aren’t easily opened by external force.

Electromechanical locks also have paved the way for the growth of biometric options; these are even more secure than using keyfobs or ID badges. Employers are now using facial recognition or finger-vein biometric authenticators. This can be easier to manage by both employees and security personnel.

### Design Flexibility

The design of solenoid locks can vary greatly by application; from simple drop-in replacements to full locking assemblies that are ready to mount into your system. This gives a large amount of flexibility and convenience in the design process; there is a solution available for all sizes of locks.

The convenience of solenoid-based locking doesn’t just extend to the design of the lock, but also the systems that use cloud-based functionality; these can predict when the locking system will need maintenance or a replacement, instead of waiting for issues to arise. This provides not only an added benefit to the end user, but to the manufacturer as well.

Johnson Electric is constantly driving innovation to better serve our customers; from simple actuators to full subsystems that integrate with the Internet of Things (IoT). Our engineering team will help you create a secure locking application that fits your unique product and security needs. We are a partner during the design process, into production and throughout the product lifecycle.

## High Force with the AC Laminate Series

September 3, 2021

AC Laminate Linear Solenoids from Johnson Electric have a T-shaped laminated designed plunger and laminated steel frame.

This platform has the unique ability to hold a hefty load, although with quiet operation. To minimize the humming or chattering of most AC solenoids, we machine the contact surfaces of the laminated frame and plunger to provide an especially smooth and flush contact surface.

Our Super-T Laminates are products developed following years of engineering, research, and manufacturing experience.

### Features and Benefits

• 10,000 Cycles
• Exceptionally High Force and Stroke Compared with DC

### Common AC Laminate Solenoid Applications

• HVAC
• Industrial Equipment

This platform is available in various frame sizes with a variety of plunger and coil arrangements; consequently, this platform is ideal for most very high force AC applications.

For further information on the AC Laminate Series, contact our office to speak to a sales representative.

## The Smooth Actuation of the SoftShift Series

August 27, 2021

Johnson Electric’s SoftShift linear solenoids provide slow, especially smooth position control or high-speed snap-action operation.

SoftShift solenoids have a unique construction that allows easy transition from snap action to variable positioning. Using the same power, the starting force is three to five times higher than standard solenoids at the fully de-energized position, which is advantageous for starting inertial loads or detent mechanisms and conserving electrical power.

This solenoid offers quiet operation, high power density, and also a variety of sizes. Custom engineered solutions additionally ensure that exact application requirements are met. With a life of 10 million cycles, the Soft Shift® platform is especially ideal for applications requiring closed-loop velocity and position control.

### SoftShift Features and Benefits

• Life of 10 Million cycles
• Slow, Smooth Motion or Snap Acting
• Can fit tight size restraints
• Quiet Operation (65dBA)
• Built-in Return Spring
• Dual Shaft Extensions for Pull or Push Use

### Common Applications

• Impact sensitive applications
• Medical Equipment Lock

For further information on the SoftShift Series, contact our office to speak to a sales representative.

## Compact Size with the Low Profile Solenoid Series

August 20, 2021

Johnson Electric’s Low Profile Linear DC Solenoids offer an extremely compact design which optimizes the magnetic flux path for maximum force versus stroke characteristics.

The construction of the plunger assembly provides an auxiliary flux path which consequently permits a significant increase in force.

The reliability and high performance of the low profile design also make it an ideal choice for applications in which consistent, reliable operation is critical.

### Features and Benefits of the Low Profile Series

• Extreme temperature applications (up to 200°C, in fact)
• Forces up to 190 lbs
• Can fit tight size restraints

### Common Applications

• Pumps
• Packaging Equipment
• Instrumentation and testing equipment

For further information on the Low Profile Linear DC Solenoids, contact our office to speak to a sales representative.

## The Powerful Ultimag® Series

August 13, 2021

Johnson Electric’s Ultimag® rotary actuator technology offers a bidirectional, center return function not found in traditional rotary solenoids.

Substantially faster than other solenoids, the Ultimag platform can operate in an on/off mode or proportionally, in both open and closed-loop systems.

Ultimag® actuators also offer a 45° stroke; however, the design can have a maximum stroke of 160°. For shorter strokes, you can of course use electronic or mechanical stops.

The Ultimag® Series was developed in response to application needs for higher speed and higher torque motion control components. This technology is also ideal for applications requiring high speed and high torque motion control.

### Ultimag Rotary Actuator Features and Benefits

• Highest Speed
• Capable of 5ms movement time*
• Long Life: up to 100 million cycles*
• No axial travel limits wear on mechanical linkages

### Common Applications

• High-Speed Industrial
• Medical Devices

For further information on the Ultimag rotary actuator, contact our office to speak to a sales representative.

## Versatility of the Rotary Series

August 6, 2021

Johnson Electric is the world leader in Rotary Solenoid technology. Rotary solenoids are electromechanical devices that convert linear motion to rotary motion by virtue of three ball bearings that travel down inclined raceways.

### How Rotary Solenoids Work:

When the coil is energized, the armature assembly is pulled towards the stator and rotated through an arc determined by the coining of the raceways.

Our 3 Ball Race rotaries are capable of withstanding a high G load shock without worrying about accidental actuation thanks to the uniquely designed helical raceways and tri-ball bearing setup.

Our standard design is capable of -55°C to +80°C ambient temperatures and the high-temperature design is capable of up to 200°C.

These extremely high-speed actuation devices provide very long-life operations for the most challenging applications.

### Features and benefits

• High Durability up to 50 million actuations
• Large variety of sizes
• Custom engineering for environmental and torque requirements
• High-Shock Resistance
• High-Temperature Resistance

### Common Applications

• Door Locking
• Machine Vending
• Industrial Automation
• Medical Diagnostic Equipment

For further information on the rotary solenoids series, contact our office to speak to a sales representative.

## Long Life with the STA Series

July 30, 2021

Johnson Electric’s extensive tubular solenoid platform provides high force for short stroke applications; it is, therefore, ideal for applications requiring long life and high reliability. We construct our Super Tubular Actuator (STA) technology with low friction system bobbins, ensuring life up to 25 million actuations.

The customizable Super Tubular Actuator platform is available in various sizes in both push and pull engagement. This also makes them well-suited for lock/latch operations.

The STA Series provides high resistance to shock and vibration to withstand extreme ambient conditions. They are additionally available in magnetic latching versions.

### STA Features and Benefits:

• Strokes up to 1.5”
• Built-in air gap spacer maximizes life while minimizing cost
• Magnetic Latches
• Rated at 25 Million Cycles
• 7 Pull and Push Models
• Easy nose mount installation also requires no additional hardware

For further information on STA technology, contact our office to speak to a sales representative.