Article

What is a solenoid valve coil?

Beris Electronic
Solenoid Valve Coil is the most important electronic control component in the solenoid valve. It is composed of copper or aluminum wire wound into a hollow form. It converts AC or DC electrical energy into linear mechanical motion to drive the solenoid valve. 

This is achieved by placing a ferromagnetic core inside the coil. In the solenoid valve, the ferromagnetic core is called the valve core. When the current flows through the coil, due to the magnetic effect of the current, a magnetic field is generated in the surrounding space, thereby magnetizing the valve core into an electromagnet, and then under the electromagnetic force, the electromagnet further slide upward into the coil, thereby opening the valve port or pilot hole to realize the on-state of the solenoid valve



Main Structure

The conventional structure of solenoid coil includes: 

Enameled copper wire

Bobbin

Pin

Yoke

Encapsulation 

In addition, according to the actual use, there will be a magnetizing guide ring, a bridge used for rectifying, etc.

1) Enameled copper wire 
Copper conductor with a coat of insulating paint on its surface, which is the core material of solenoid coil. Solenoid coils used in valves are designed and tested for continuous service. They all meet the thermal endurance specifications according to IEC 216.

Insulation class Allowable Max. Temp. Rise ℃ Allowable Max. Oper. Temp. ℃
B 90 130
F 115 155
H 140 180
N 160 200
R 180 220
Remarks: This clause does not apply to pulsation operated coils

2) Bobbin
The bobbin is the carrier of enameled wire winding. According to the temperature rise of the coil and the actual use environment, different bobbin materials are selected, such as PA66, PPS, PBT, PET, etc., and a few of them are thermosetting BMC and PT-310

3) Pin
 The function of pin is to realize the electrical connection between the internal enameled wire and the external. Similar to the same function, there are pins, terminals, flying leads, etc. Pin material is generally brass, such as H59, H62, H65, of which H62 is the majority.

4) Yoke

It is used to gather the magnetic field lines from the N pole to the S pole, increase the magnetic field strength and minimize the magnetic leakage into the air. A reasonable support structure design is conducive to improving the magnetic field strength. Generally, there are two kinds of support materials: low carbon steel cold-rolled plate and electrical pure iron (DT4C).


5) Encapsulation

It is used to combine coil parts into a whole, which plays a role of waterproof and dustproof. The plastic covered materials include thermosetting plastics and thermoplastic plastics.


Thermoplastic: this kind of plastic is characterized by being soft with the increase of temperature, being molded and hard after cooling. This process can be repeated many times. The thermoplastic coil has good weather resistance and toughness. The most common material is PA66, followed by PA6


Thermosetting plastic: this kind of plastic is characterized by curing at a certain temperature, after a certain time of heating or adding curing agent. The solidified plastic is hard and insoluble in solvent, and cannot be softened by heating. If the temperature is too high, it will decompose. The thermosetting coil has high temperature resistance, small shrinkage and flat shape during injection molding. At present, all the thermosetting materials are BMC, but the content and formula of glass fiber are slightly different



Solenoid coil classification  
Classification by application:  Pneumatic industry; Hydraulic industry; Household electrical appliances; Textiles industry; Refrigeration industry; Automobile industry; Explosion protection industry, and so on.

Classification by manufacturing process:  Thermosetting/Thermoplastic/Non encapsulation;


Solenoid coil performance
Degrees of Protection:
Degrees of protection provided by electrical enclosures (IP Code), According to standards EN 60529 and IEC 529


The code letters IP (Ingress Protection) followed by 2 characteristic numerals: e.g. IP65.The first figure indicates the degree of protection of the energized parts and internal moving parts against ingress of solid foreign objects. The second figure indicates the degree of protection against ingress of water with harmful effects.


The encapsulation coil can generally reach IP64 or IP65; Water-proof coil can reach IP67


Turns
Measured by coil turns meter, usually the turn’s tolerance follows below standard
Turns Turn tolerance
0~300 0
300~500 ±3 Turns
500~20000 ±0.6%
20000~60000 ±1.5%

Resistance

① unless otherwise specified, the coil resistance value is the resistance value at 20 ℃;

② When the standard resistance value is

When the standard resistance value is ≥ 1000 Ω, the resistance tolerance range is ± 7%

Standard resistance conversion formula when the ambient temperature is not at 20 ℃

R2=R1×(T2+234.5)÷(234.5+20)

T2:Current ambient temperature; 

R1: Standard resistance at 20 ℃; 

R2:Resistance at current temperature。


Insulation resistance: 
The insulation resistance between the power terminal and the grounding terminal shall not be less than 100m Ω under the environment of temperature (15-35) ℃ and relative humidity not more than 85% 

Voltage level of insulation resistance measuring instrument:
Rated voltage U (V) Voltage level of insulation resistance measuring instrument
U ≥250
60≤U ≥500
300≤U ≥1000

Grounding resistance: 
Use resistance tester to measure the resistance between the grounding terminal and the yoke, and the resistance between the grounding terminal and the Yoke or the metal surface shall be less than 1 Ω.

Coil temperature rise:
① test according to JB / T 6378; 

② the temperature rise of coil assembly and the maximum temperature obtained by temperature environment shall not exceed the following table. 


Withstand voltage test :

Use the power frequency withstand voltage tester to apply the test voltage specified in the table below between the power supply terminal and the grounding terminal, set the leakage current to 1mA, apply the type test for 1min, apply the factory test for 1s (test voltage increases by 10%), and there shall be no breakdown, discharge or flashover.


Turn to turn withstand voltage test

Take one as the reference coil, and then take any one as the tested coil. Apply the impulse voltage wave specified in the following table between the two coil terminals or between the head and tail outgoing lines. The test time is 1-3s. Compare the difference between the two oscillation waveforms. The waveforms should be consistent, and the product difference is less than 20%.

Rated voltage U (V) Withstand voltage and Turn to turn withstand voltage test (v)
U ≥1000
60≤U ≥2000
300≤U ≥2500

Corrosion resistance:
Coil integral parts or corresponding metal parts shall be subject to continuous salt spray test for not less than 24 hours in accordance with GB / T 2423.17 or according to customer requirements (such as automobile products). After the test, the metal coating and coating surface shall be free of rust.

Appearance: 
No defect such as scar, deformation, crack, bubble, etc.

Tension of power line: 
the power line, coil shell and connecting terminal shall bear the following pressure without visible damage.
Rated magnetic cross-sectional area mm²  AWG wire gauge Tensile force Rated magnetic cross-sectional area mm²  AWG wire gauge Tensile force
       
0.08 28 8.9 0.75 18 89
0.13 26 13.4 1 104
0.2 24 22.3 1.5 16 134
0.34 22 35.6 2.5 14 223
0.5 20 57.9 4 12 312


Critic Information for a new solenoid valve coil development

1. Working voltage
The frequency shall be provided for AC, and the power difference between 50Hz and 60Hz of the same coil is about 1.2 times, for example: 7.2W for 50Hz and 6.0w for 60Hz; 60Hz for 50Hz coil, and the voltage difference is about 1.095 times, for example, AC220V50HZ and AC240V 60Hz coil are universal)
2. Power or resistance
3. Armature’s Diameter, or Coil’s hole and aperture
4. Working environment:  temperature, humidity, indoor or outdoor, protection, etc
5. Connection with external power supply: pin type/leading wire type/standard interface, etc.
6. Application
7. Other requirements: such as environmental protection material requirements or certification

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