SOLENOIDS CONCEPTS

Solenoids/coils are electromechanical devices, which convert electrical energy into mechanical motion. They are composed by: a fixed core, an electric coil and a guide tube in which the mobile plunger slides. The supply applied to electric coil produces the plunger movement that provides a force, whose value increases as the value of current increases and as plunger approaches to its mechanical end stop that is the solenoid's fixed core. The plunger is linked, directly or indirectly, to the regulation mechanism of a valve or to the mechanism that operates; it can operate according to two main options:

- PULL
- PUSH

With the coil de-energized, the plunger return motion is provided by the load itself and/or by a return spring which can be provided as an integral part of the solenoid/ coil assembly.

SOLENOID CHOICE FACTORS

A number of mechanical, electrical and thermal factors should influence the decision-making process when you are selecting the most effective and efficient solenoid/coil for a particular application. Striking the right balance among these factors is critical to make the right choice. These pages are designed to aid you with this process. Furthermore our engineering experts will work together with you to make sure you get the most effective solution. We focus all our resources and skills on providing you the best combination of price and performance available.
We can help you evaluate your needs in terms of:

- FORCE/STROKE REQUIREMENTS
- ELECTRICAL REQUIREMENTS
- DUTY CYCLE
- MAXIMUM ENVELOPE DIMENSIONS
- ENVIRONMENTAL FACTORS
- MINIMUM AND MAXIMUM ACHIEVABLE TEMPERATURES
- OPERATING ENVIRONMENT
- MECHANICAL AND ELECTRICAL CONNECTIONS

FORCE / STROKE

Solenoid/coil force is the pull or push force developed by the plunger when the coil is activated.
A number of interrelated factors influence the solenoid/coil force/stroke relationship. Voltage, temperature, and duty cycle all affect the force your solenoid/coil is capable of pulling or pushing. Also, the force capability increases as the stroke length decreases.
Variations in supply voltage greatly affect the force/stroke characteristic of a solenoid/coil. It is good practice to select a solenoid/coil force/stroke based upon the lowest supply voltage and power. When selecting the proper solenoid/coil, remember to consider all forces against which the coil must work to move and seat the plunger. In addition to the external load to be moved, often the effects of a return spring must be considered. If one is used, its force must be subtracted from the force available to do work to arrive at net force needed.

MECHANICAL LIFE

Our technicians try to guarantee a longer life to the solenoid / coil by making sure that the force generated by the solenoid / coil coincides strictly with the load requirements. Solenoids / coils that generate excess force are subject to overloads and impacts between mechanical elements that can cause failures. Correct alignment of the mobile core helps to ensure excellent performance and a longer life of the equipment.

FORCE / STROKE CURVES

The industry has used force / stroke curves for a long time to evaluate the performance of the solenoids / coils and to have help in selecting the solenoid / coil from them. These curves can be useful tools; in any case, care must be taken when comparing different product lines because their data could be based on different models. Many factors influence these curves, such as:

- GEOMETRY OF THE MOBILE CORE
- DIAMETER OF THE MOBILE CORE
- COIL / SOLENOID TEMPERATURE
- LARGE SPOOLS OF THE COIL / SOLENOID < br> - APPLIED POWER
- WORK CYCLE

The performance graph underlines the importance of understanding how force / stroke curves are determined. These curves represent the minimum performance of a design model. If different configurations of solenoids / coils are evaluated, it is necessary to make sure to understand the reference conditions well before making the final choice. We can supply solenoid / coil samples to be able to test the actual application conditions.

POWER / TEMPERATURE

Operating solenoid/coil temperature greatly influences the solenoid/coil force delivers at a given applied voltage. Solenoid/coil resistance increase as solenoid/coil temperature goes up. This causes a reduction in applied voltage and resulting mechanical force. The solenoids/ coils rising temperature (ØT) calculation is carried out with the following formula:

                                     ØT = (R2-R1) : R1 x (234,5 t1) – (t2 – t1)
Where:
R1       is the coil resistance value at the test start.
R2       is the coil resistance value after the achieved coil thermal stabilization.
234,5   is the constant k of copper.
t1        is the ambient temperature at the test start.
t2        is the ambient temperature at the test end.

LOAD / POWER

Solenoids/coils can be designed to operate from either AC or DC power. DC power is preferable for most applications because of design flexibility, solenoid/coil reliability, less electrical noise and more consistent operating speed. Variations in nominal voltage greatly affect solenoid/coil force/stroke characteristics, so it is important to select force/stroke performance based on lowest anticipated input voltage. The current and the number of wire turns determine the solenoid’s/coil’s magnetic flux. The current limitations are determined by your specifications requirements.
The number of wire turns are limited by the physical constraints of the mechanical package and by coil/solenoid temperature. Magnetic solenoids/coils ensure the most efficient design by decreasing size and weight as allowable temperature increases.

DUTY CYCLE

Duty cycle is the ratio of time “on“ to total cycle time for solenoid/coil operation, and it should be kept to a minimum. It is expressed as:

                                          (On time)
Duty Cycle (%) = -------------------------------- x 100
                                    (On time Off time)

Continuous operation solenoids/coils (work cycle at 100%) guarantee a safety margin against overheating and coil breaks, but provide less force than discontinuous or intermittent operation solutions (less than 100% of the work cycle).
Our technicians can help you choose discontinuous operation solenoids/coils that guarantee the desired force with the smallest dimensions and minimum possible overheating. We can also help to ensure the maximum “on” time without exceeding the recommended limit for a certain solenoid/coil. If the application allows it, the voltage of the solenoid/coil can be reduced when the moving core has come into contact with the fixed core. Although the retention force of this position with less applied voltage decreases, it may be sufficient to allow for the initial power to be lowered and heat build-up and power consumption to be reduced.

AMBIENT TEMPERATURE

The ambient temperature in which the solenoid/coil is going to operate can greatly affect performance. The maximum operating temperature for any solenoid/coil is a product of the temperature rating of the insulating/encapsulating materials.
Standard magnetic solenoids/coils use Class “F“ or “H“ insulation which permits maximum allowable total coil temperature to rise to 155 °C or 180 °C.

Insulation class                  Maximum temperature
            A                                       105 °C
            B                                       130 °C
            F                                       155 °C
            H                                       180 °C
            N                                       200 °C
            R                                       220 °C
            S                                       240 °C

ELECTRICAL CONNECTIONS

To supply electrical power we can use many different types of connections like: DIN, Deutsch, AMP Junior, flying leads etc.

DIMENSIONAL CONFIGURATIONS

Dimensional configurations and physical space limitations inherent in many applications can have a critical effect on overall solenoid/coil performance.
Four factors especially influence the selection decision:
1. Space available helps determine solenoid/coil size and has an important bearing on operating heat factors.
2. Once you fully understand space limitations and solenoid/coil size, it is important to consider the proper solenoid/coil configuration for its assembling.
3. Space and mounting orientation, mechanical and electrical connections also influence desired performance characteristic.
4. Finally, you need to carefully consider the most effective method to match the solenoid/coil with the others finished product elements to ensure the maximum system efficiency.