How to regulate speed of 24V DC fan with PLC and SSRs from Aliexpress?

Question:

Hello, I purchased a programmable logic controller (PLC) with a human-machine interface (HMI) from Aliexpress, specifically the model with solid-state relays (SSRs) on the right side. I am looking to connect a 24V/0.2A DC fan to the output, but I am unsure how to regulate the fan speed given that the output switches are SSRs. How can I adjust the speed of the DC fan in this setup?

Top Replies

eagl1 inquired about controlling the speed of a 24V/0.2A DC fan connected to a PLC + HMI purchased from Aliexpress. The specific model with SSRs, rather than mechanical relays, and a "transistor" output is recommended for this purpose. By utilizing the pulsed output feature, which is typically PWM, the fan speed can be adjusted by selecting a carrier frequency and adjusting the duty cycle. While the fan may struggle at 50% speed, reasonable control can be achieved between 60% and 100%. For those looking to upgrade to more advanced technology, this approach offers a modern solution for fan speed control.

The relay output on the right is not solid state, while the one on the left is a transistor. Both have analogues with 0-10V input/output, but you will need a converter to vary the motor speed by converting 0-10V to 0-24V. Keep in mind that a 24V DC motor may not have sufficient torque at low voltages or may not run at certain points. It's important to note that the analog outputs are not isolated, so caution is advised to avoid damaging them.

Tinine recommended specifying the actual model number instead of referring to "the one on the right." The model on the right features mechanical relays, while the closest alternative with SSRs seems to be the "transistor" output. Specifically, I am referring to the FX3U-14MR model with relays, as I need to regulate other AC outputs. However, my current dilemma is how to adjust the speed of a 24V DC fan.

To regulate the speed of a motor, one must utilize the analog outputs in conjunction with a DC motor controller equipped with a 0-10v input for speed adjustments. While often mistaken for an FX3U, the actual model is closer to the older FX2N. Accessing the built-in analog outputs requires the use of functions RD3A & WR3A. The baudrate typically remains fixed at 19200 for programming purposes. Unlike the FX series, it is not possible to write PLC parameters in this model.

Eagl1 expressed a concern about controlling the speed of a 24V DC fan. Looking for affordable options on Aliexpress may be a good idea. However, finding ways to regulate the fan's speed is crucial.

Hey there! You could implement PWM (Pulse Width Modulation) to control the speed of your DC fan despite your PLC having SSRs. By adjusting the duty cycle of the PWM signal, you could somewhat modify the effective voltage supplied to the fan, hence varying its speed. However, the SSR has to be compatible with the PWM frequency. Otherwise, the SSR could be too slow to effectively switch on and off at the high frequency, leading to significant losses. So, do check your components' datasheets to confirm whether this setup would work as expected.

To regulate the speed of your 24V DC fan in this setup with SSRs, you might want to consider using a Pulse Width Modulation (PWM) approach if your PLC supports it. Instead of connecting the fan directly to the SSR output, you could use a PWM signal from the PLC to control a driver that modulates the fan speed. If your HMI allows it, you could adjust the duty cycle of the PWM signal to effectively control how much power the fan receives, thus varying its speed. Just make sure to check the fan specifications to confirm it can handle PWM control! Alternatively, if PWM isn't an option, using a variable resistor or a DC fan speed controller could be another solution, but they may not allow the same level of precision or automation.

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Frequently Asked Questions (FAQ)

FAQ: 1. How can I regulate the speed of a 24V DC fan using a PLC and SSRs from Aliexpress?

Answer: Answer: To regulate the speed of a 24V DC fan with a PLC and SSRs, you can use pulse width modulation (PWM) technique. By varying the duty cycle of the PWM signal sent to the SSR controlling the fan, you can adjust the speed effectively.

FAQ: 2. Can I directly connect the 24V/0.2A DC fan to the SSR output of the PLC?

Answer: Answer: Yes, you can connect the 24V/0.2A DC fan to the SSR output of the PLC. Ensure that the fan's power requirements are within the specifications supported by the SSR to prevent any damage.

FAQ: 3. How do I implement PWM control for the DC fan speed through the PLC and SSR setup?

Answer: Answer: You can program the PLC to generate a PWM signal by toggling the SSR at varying duty cycles. By adjusting the on and off times of the SSR output, you can control the speed of the connected DC fan effectively.

FAQ: 4. Are there any specific considerations or precautions to keep in mind when regulating the speed of a DC fan with SSRs and a PLC?

Answer: Answer: When using SSRs to control the speed of a DC fan through a PLC, ensure that the fan's current and voltage ratings are compatible with the SSR specifications. Additionally, implement proper thermal

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