Basically a solenoid consists of a coil with an associated iron circuit forming the fixed part. A moving plunger is pulled into this coil when it is energized. The diagram below show a basic open frame solenoid.

Solenoids have a electromechanical pull action. This pull action can be converted to a pushing action by fitting a suitable thrust pin or plunger extension still using the same open frame solenoid.

Duty cycle is the term used do define the heating factors of a solenoid to prevent thermal damage. Duty cycle is normally expressed as a percentage and is defined as: the solenoids ¡°on time¡± divided by the sum of the ¡°on time¡± plus the ¡°off time¡±:

 Duty Cycle(%) = [ON TIME / (ON TIME + OFF TIME)] X 100 £¨%£©

Duty cycle is important because a by-product of applying electrical power to the coil is heat. The excess heat can thermally damage the coil. Thus the term duty cycle is used to assure that only the safe maximum amount of electrical energy is applied to the solenoid.

All coils for our standard solenoids are wound to order on demand. Therefore it is no problem to accommodate a special winding for "in between" duty cycles or special voltages or temperature conditions in our standard solenoids.

¡ñMaximum ¡°On¡± Time

When a solenoid is actuated, current is applied to the coil. A by-product of this is temperature rise in the coil. When a solenoid is energized continuously, heating of the coil increases until a saturation lever is reached which is equal to the ambient heat radiation. When a solenoid is operated in an intermittent (on-off) manner, the ¡°on¡± time becomes critical if higher voltages (thus currents) are applied to the coil. These higher currents cause higher coil temperatures which can exceed the cooling capacity of the solenoid through ambient radiation. This heat rise can thermally destroy the solenoid¡¯s coil. To avoid such a catastrophic failure, there is a maximum ¡°on¡± time, which is the longest time the solenoid can be energized without thermal damage. The maximum ¡°on¡± time has been determined for each duty cycle, and is shown in the temperature rise vs. time tables.

¡ñForce vs. Stroke Characteristics Tables

Tables are provided for each size of tubular solenoids, open frame solenoids, and keep  solenoids, which show stroke vs. force curves at four duty cycles (100%, 50%, 25%, and 10%). When you have made certain the force, stroke, power or duty cycle, you can select a appropriate solenoid by these tables.

¡ñSafety Factor of Force

To reduce potential problems due to energy less through temperature rise in the coil and voltage fluctuations, a safety factor of 1.5 is recommended (required output X 1.5). When using open frame solenoids and self-holding solenoids, the safety factor should be 1.3. It is possible to use a smaller safety factor, but precise application testing should be performed under all possible conditions.

¡ñTemperature Effects on Performance

Coil and performance data shown in this catalog are measured an ambient temperature of 20¡æ. When a voltage is applied to a coil, the coil temperature rises (see time vs. temperature rise tables). This temperature increase causes an increase in the coil resistance. As a result, the energy output will decrease. The relationship between the coil temperature and the coil resistance are shown in the following table.

To select the appropriate solenoid, it is necessary to consider the final temperature of the solenoid in your application. To determine the value of force after the coil temperature increase, the ampere turns must be calculated from ambient temperature based on the following formula:

t = [(R2 ¨C R1)/R1]X(234.5+t1)+t1-t2

t: temperature rise (deg.)

R1: initial coil resistance (ohms)

R2: final coil resistance (ohms)

t1: initial ambient temperature (¡æ)

t2: final ambient temperature(¡æ)

¡ñHeat Sink

In order to reduce coil heating and to enable a larger number of ampere turns to be employed, a heat sink is attached to a solenoid. Heat sink can increase on duty cycle and maximum ¡°on¡± time of a solenoid.

¡ñResponse Time

The response time for solenoids is the time from when a voltage is applied to the coil until a given stroke has been achieved. Two main factors contribute to the overall response time. One is time it takes the current to overcome coil inductance and develop the required magnetic flux field. The other is the time it takes for the plunger to actually travel the stroke distance. Flux build-up normally takes more than half of the total response time. Generally speaking, the response time varies between 5 milliseconds for small size units at short strokes up to 250 milliseconds for long stroke, larger sizes.

¡ñMounting and Electrical Connection

Mounting styles include screw mounting and clip mounting. Screw mounting is commonly applied, and clip mounting can improve efficiency.

Electrical power can be supplied to the solenoid through a variety of types of connections. Common types are leads and #187 quick connect terminals.

¡ñGeneral Plunger Styles

When you select the plunger style, you should assure required freeness of the mechanical structure. A side load on the plunger will cause performance deficiencies and excessive wear.

¡ñOhm¡¯s Low and Power

When the current in coil leans to stability, the relationship among current(I), voltage(U) and resistance(R) obeys ohm¡¯s low: R=U/l

About power: W= U²/R=I²XR

¡ñRelational Circuits (advice)

Power supply

All of our standard solenoids are DC type. If the power supply available is AC, then a rectifier is required to convert AC to DC. The rectifier should be a full wave rectified type. The right circuit is commonly applied.

Circuits protection

The solenoid coil is an inductive load which has a high inductance. As such, caution should be taken in the form of arc suppression when energizing and de-energizing the coil. The diagrams below show the circuits to protect the control contacts or dynatron.

pick and hold Circuit

This circuit is used when a large energy output from the solenoid is required, but the space is limited. The circuit applies an extremely high voltage to a coil during energizing(pick) and then applied a voltage to the coil to reduce potential coil heating problems (hold). The most frequently used method is to use a simple timing circuit that applies a high voltage signal for approximately 50msec. and then drops off to a holding voltage. There are also dual coil designs whereby one coil is used for ¡°pick¡± and the other for the ¡°hold¡±.

Circuits to energize keep solenoid

For keep solenoid, it is important to apply the correct amplitude releasing voltage.

Electrolytic corrosion of coil

When the solenoid is used in an environment of high temperature and high humidity, and the case is grounded, the coil may corrode and fail under electrolytic action. To eliminate this potential problem, the following precautions should be observed.

1.      Ground the positive(+) lead of the power source.

2.      When circumstances preclude the grounding of the positive(+) lead of the power supply, or require the grounding of the negative(-) lead of the power supply, install a switch in the positive(+) lead of the power supply and connect the negative(-) lead to the coil.

¡ñService cycle life

Standard construction nominally rated for 1,000,000 cycles. In actual service, cycle life exceeding this figure is constantly being experienced. Periodic cleaning and lubrication will help in extending life. Severe operating conditions - a heavy side load on the plunger, for example may shorten cycle life. Since many factors other than the solenoid construction itself have their effect, the rated life expectancy is valid only for the laboratory conditions under which life tests were run. Special long life designs are available.

¡ñConversion of Units (Reference)

¡ñOrdering Information Required

1.      pull or push type

2.      power or operation voltage and current limitation

3.      duty cycle: continuous, intermittent or pulse

4.      maximum ¡°on¡± time

5.      force-stroke requirements

6.      coil termination

7.      special features