Solenoids


#1

This post is meant to give some general information on solenoids.

General Operation

  • A solenoids operating principle is very basic. A solenoid consist of a coil and plunger that are housed together. When the coil is energized the current flow results in a magnetic force which acts upon the plunger.
  • Whether the magnetic force pushes or pulls on the plunger is determined by how the coil is wound. Simply switching the polarity of the leads will not change a solenoid from push to pull (the solenoid will do what it is wired to do, polarity doesn’t matter).
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Uses

Due to their small size and considerable pushing/pulling capability, solenoids are incorporated into many different applications. Some examples being…

  • Vending machines
  • Copiers
  • Pumps
  • Locks
  • Brakes
  • Gear positioning
  • Packaging and Sorting equipment

Types

  • Digi-Key offers solenoids in two basic frame types so our customers are given a couple different mounting options.
    • Tubular solenoids that have a threaded bushing that make them easy to panel mount.
    • Open frames solenoids that have threaded inserts that allow them to be chassis mounted.
  • Most of the solenoids that we carry are pull type but we do list a few push types as well (our current catalog page is shown on the next slide).

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Specifications

There are a few specifications that need to be considered when selecting a solenoid.

  • Frame type - Where is the solenoid being mounted
  • Voltage - What voltages sources does the customer have
  • Power - Dictated by the stroke length and operating force
  • Stroke length
  • Operating force
  • Push vs Pull
  • Standard or Latching
  • Duty Cycle – Explained below

Duty Cycle

  • Continuous – These solenoids can be actuated indefinitely, meaning a voltage can remain present on the coil for as long as it needs to be there. This type generally has the least amount of power and pull force.
  • Intermittent – These solenoids are actuated for a short amount of time and then deactivated to allow for coil cool down. If these are left on for too long the coil will burn out. Usually this is 1 minute on max and 3 minutes off min. Compared to the continuous option, these are higher power with high pull force.
  • Pulse – These solenoids are actuated just long enough for the plunger to seat (pull in) and then deactivated to allow for coil cool down. If these are left on for too long the coil will burn out. The time is usually 100msec on and 900msec off. These are the highest power and the highest pull force.

Standard vs Latching

  • Comparing the datasheets for each solenoid you will notice that the latching solenoids include a release voltage specification.
  • Unlike the standard solenoid, latching versions are polarized. Applying a voltage one way will pull the plunger in. Applying a lower reverse voltage will cause the coil to produce enough opposing magnetic flux to cancel the effect of the fixed magnet. Since the magnetic force is only canceled, an added spring is necessary to expel the plunger.