Solenoid Valve Coil Voltages: What's the difference?
Solenoid valves are controlled by electrisation of a solenoid coil, which when electralised, produce a magnetic field that results in some further desired effect: e.g. the movement of a spool within a valve body, thereby changing the pneumatic flow path.
However, solenoid coils can differ by the voltage they were designed to operate with. The most common voltages for solenoid valves are DC24v, AC110v, AC220v, and the other possible voltages being DC12v and AC24v. Each voltage has their advantages and disadvantages, and we will outline them below.
Figure 1. Typical Solenoid Valve Coil
1. Cost
The cost of building a pneumatic system to be used with DC (direct current) supply is greater than a system with AC (alternating current) supply. This is because the operating current of DC supply is higher than that of AC supply, and procedures must be in place to preclude voltage drops on the return line
2. Inrush Current and Holding Current
However, AC solenoids often have a high inrush current followed by a low holding current. One consequence is that when the spool jams, there is constant high current which can damage the coil via overuse and/or overheating. This result is otherwise known as a coil 'burn out', and are almost exclusive to AC coils. However, burn out coils may not be due to a fault in the coil, but due to a fault in the valve; namely, a jammed spool.
Further Considerations:
3. Undervoltage
For pneumatic solenoid valve coils, there is usually a working range of ±15% of rated voltage. For example, if the rated voltage is AC220v, then the minimum working end of the voltage would be ~AC187v. However, if the voltage is too low, the technician may experience a number of symptoms
- The spool cannot pull in and there is coil burnout
- Slower response time of the valve
- Excessive noise coming from the coil
- Overheating of the coil
If you experience these symptoms, use a multimeter to check the supply voltage to the solenoid valve coil. If the supplied voltage is close to the rated voltage, then the coil may be at fault. It is advisable to replace the coil
4. Overvoltage
Coils in pneumatic solenoid valves can also be overvolted. In these cases, there will be a greater response time from the valve – e.g. the spool moves quicker – which may be a desired effect. This is not to say that the pneumatic cylinder will actuate faster, but that there is less time between electrisation of the coil, and the change in flow path. Some operators may even intentionally overvolt a solenoid coil.
However, since more volts are being draw, there is more power consumption. And, subsequently, there will be more thermal waste. This could result in overheating of the coil and burnout.