Solenoid selection guide

Minimum requirements for solenoid selection.

The following are needed as a minimum to enable solenoid selection

Function required: pull / push / rotary/ latching / locking / etc
Stroke movement: travel in mm / inches
Force needed: Newtons / Kgf /  Pounds / etc
Duty cycle: on time / off time ratio
Power supply: voltage / AC or DC

 

Additional information to assist in making a solenoid selection
Operating life: how many cycles
Environment: ambient temperature / wet or dry / clean or dusty/ vibration / etc
Installation factors: space envelope / mounting preference / plunger design
Power supply factors: any power (Watts) or current (Amps) limitations in the system

 

Solenoid construction
When selecting a solenoid it is useful to know something about the basic features and characteristics :

  • A solenoid is a linear actuator in which, when the coil is energised, the armature (plunger) is Pulled in to the pole piece (stop).
  • If a Push function is wanted, then a non-magnetic push-rod is required – see Fig 1.
  • Rotary solenoids are selected in much the same way, except that instead of a linear stroke, there is an arc of rotation.
  • Generally the force increases as the armature closes on the pole piece – see Fig 2.
  • The Duty Rating (%) defines the power of the coil in the solenoid and is the ratio of the ON time to the total time per cycle of operation.
Duty Cycle  =
time ON
X 100%
(time ON + time OFF)

 

Examples

  • a Continuously Rated (100%) coil may be energised indefinitely but has a lower power consumption resulting in lower magnetic force
  • a Short-Rated (e.g. 25%) coil has more force but must be switched off for part of the cycle

Further details and technical definitions can be found in Technical Explanation GXX

Fig 1. Linear solenoid, bearing construction Fig 2. Force Characteristic
Linear solenoid, bearing construction Force Characteristic

 

AC solenoid vs DC solenoid? Pro’s & cons :
AC solenoids

  • have an in-rush current, providing high initial stroke force
  • can utilise longer strokes than DC solenoids for the above reason
  • may hum in operation, according to the application conditions
  • the armature (plunger) must always be allowed to seat, otherwise over-heating of the coil may occur.

DC solenoids

  • are generally quieter in operation
  • have longer operating life (bearing construction versions)
  • any DC Solenoid can be operated from an AC supply via a simple bridge-rectifier, also available from us – ask for details.

 

Other solenoid types
There are many other variations in solenoid design which may incorporate features such as

  • 2 coils & 2 pole pieces
  • permanent magnets
  • different force/stroke characteristics ; proportional, decreasing

Details on these and many others can be found in the product-specific data sheets, or contact us on 01483 794700 or contact a technical expert.