Simple PLC Fan Speed Control (What part do I need)

Hi,

I am currently working on a little project and I am wanting to control a fans speed with some PLC digital outputs / anolog output but unsure what device would allow this. Yes there are VFD but not looking at spending that money as it will properly sit there on the works shelf for years.

Is there a cheaper option, just wondering if anyone else has done anything similar.

The PLC can only provide a signal as to what speed to run, it cannot directly control the fan itself. You need a power control device of some sort.

What you need or how you would interface with it must start with the nature of the “fan”, because that description alone is way way too vague. Without knowing what you are dealing with there is no meaningful answer to your query.

Depending on the size of the Fans(Motors)?

Take the plc out of the picture and just use a simple VFD.

There is really no need to have a PLC just to control fan speed.

damica1 said:

Depending on the size of the Fans(Motors)?

Take the plc out of the picture and just use a simple VFD.

There is really no need to have a PLC just to control fan speed.

Click to expand...

Hi, I have the PLC and HMi already and would like to of possible control the speed with a simpe +/- button on HMI

If it was a DC motor you could Google a variable speed control circuit and use the 0-10V DC PLC output to control it.


For an AC motor I would think a TRIAC control - but I am not sure how to have a DC signal control the AC TRIAC output. This is done in the field, but my quick Google search didn't show a schematic like this.


EDIT: More searching shows a couple of circuits using Arduino, I would check that option out.

I have moved on from using actual fans or motors or anything else for simulations. You learn a lot more by programming one PLC to do the controlling and a second to be the thing that is controlled. At its simplest the second PLC will have LEDs that light up when an input is energised, and outputs that do the same. You might have to learn some html to program an internal web page to show the state of analogue inputs, or free HMI software to visualise data. And with a bit of maths the controlled PLC can simulate all sorts of things. Besides it is a lot safer having a webpage showing the simulated speed of a motor rather than 240V on to a fan with actual spinning blades. The only bit I miss is the sound of something changing speed, which if I could be bothered could be simulated with a high speed output and a small amplifier.

I dont know what size fan you've got but to give an idea of cost, VSDs arent that expensive, you can easily pick up a 0.37kw for around £100.

Depends on your fan, it may be cheaper to relay different size resistors in series with the fan connections, that would reduce speed (bigger the resistor, slower speed). That method is likely cheaper and can integrate with PLC but waste a lot of energy.

If you really want to be simple, pulse your fan control relay/contactor on and off. Example 1 second on, 1 second off would maybe half your speed, totally depends on fan size etc, definitely not a industry method.

Thank you all for the replies, i have some things to think about and see what the best method to do all this is.