VFDs in Automatic Car Wash Equipment
VFD or Variable Frequency Drives are the devices that are used to safeguard the motor and have options like multiple speeds, DC injection etc.
In this article, we shall discuss how Variable Frequency Drives (VFD) play an important role in the operations of Automatic Car Wash Systems .
Often times, you might have heard about variable frequency drive is being offered to you in your equipment. However, before we go ahead and start talking about VFDs we should understand how Motors work. Motors are the drivers which help in the motion of various components in the Automatic Car Wash Machine. Motions like brush rotation, trolley movement, Brush movement etc. are done with the help of motors.
These motors typically run at an rpm or rotations per minute of 900 to 3600 rpm. However, neither the Brushes nor the other moving parts would be able to work at such high speeds. For this reason, the motor speed is reduced to usable speeds like 40 to 120 rpm using a gearbox. The gearbox reduces the speed using a combination of gears which helps in reducing the speed while increasing the torque. Torque, in simple words, is nothing but the amount of rotary force that the output shaft can exert to perform any task.
With the help of gearbox, the speed does reduce however for performing various functions in an Automatic Car Wash Machine you need to have a motor with different speeds. The gearbox may be able to reduce the speed however the speed does remain constant depending upon the gear ratio it is designed for. What it means is that once the gearbox and motor are selected, you cannot change the speed of the motor.
So now, to have multiple speeds you need to have such a device that may be able to reduce or increase the speed depending upon the requirement. Some of our electrical experts might say that you can use multi-speed motors to have multiple speeds. Yes, you’re right, but these speeds are limited to 2 or three at the most. And also these motors are a bit bulkier and non-standard with regards to their mounting on the gearbox and also with their availability as per the production schedule. Sometimes if the motor gets burnt you might not get such specially made Motors off the shelf in your local market as they are custom designed.
Now again, we come to our original problem of needing multiple speeds depending upon the various car wash programme cycles. To give you an idea, a soap spray cycle needs intermediate speed while a pre-rinse can be done at a much higher travel speed. Brush cycles also require lesser speeds during operation.
This is where the variable frequency drives come in. The electrical motors work on the principle of change in EMF which causes the rotation of the shaft of the motor. The change in EMF which is the electromagnetic force happens at the rate of the frequency of the input Power supply. In different countries, you have different cycles which range from 50 Hz to 60 Hz. A 2 pole motor That runs at 3000 rpm at 50 Hz would proportionally work at 3600 rpm at 60 Hz frequency. This way you can change the rpm of the motor without changing the voltage or limiting the current to the motor. You can reduce the frequency of the supply to the motor to get lesser speeds. You can go as low as 20 Hz or as high as 80 Hz depending upon the duty for which the motor is designed for.
Now that you understand how the speed can be changed, let's see how the VFDs do it. One of the main components of a VFD is IGBT ( Insulated Gate Bipolar Transistor ) which acts as a gatekeeper and only allows the gate to be opened when the voltage is applied. This way it converts the AC voltage to DC like voltage which is a straight line if you see the chart below. Once you have DC voltage, this DC voltage can be modified as per the requirements specified in the VFD program.
If you see the output of the VFD, it is a square wave and not a sinusoidal wave since the VFD is a digital device and uses PWM (Pulse Width Modulation) to control the speed of the motors. If you have seen motors using a VFD, you would have noticed that the motors make a humming noise. This is due to the square wave which is being supplied to the motor. This is one of the reasons why motors need to be of VFD duty or Inverter Duty. A motor that is not built to be operated by a VFD might overheat and fail.
The VFDs are programmable and can be easily customised for the way you want the motor to operate. Below is a simple program for Mitsubishi D700 VFD for KKE Speedoclean Car Wash Equipment with a 2-speed configuration.
|Sr No.||Parameter||Parameter Name||Default value||Programmed value|
|5||4||Multi high frequency||50||70|
|8||9||Electronic thermal O/L relay||0||2.2|
If you notice, that there are parameters and they have specific values. The VFD needs to know what is connected to it and how it needs to operate. Some of the features which are important for Automatic Car Wash Equipment are :
- Acceleration Time
- Deceleration Time
- Breaking or Stoping
- Multi Speeds
- Motor Safety
Acceleration and Deceleration help in reducing jerky movements of the Trolley and also help in increasing the life of motors and the gearboxes.
If you see the video below, you would notice how easy it is to configure the VFD or Inverter in an Automatic Car Wash Machine.
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