How to control speed of a 24V fan ?

[eagl1]

Hi,

I've bought this PLC + HMI from Aliexpress, the one on the right that uses SSRs.

and want to connect a 24V/0.2A DC fan to the output.

My question is how to control the speed of the DC fan at this point ? since the output switches are SSRs.

 

[Tinine]

Hi,

I've bought this PLC + HMI from Aliexpress, the one on the right that uses SSRs.

and want to connect a 24V/0.2A DC fan to the output.

My question is how to control the speed of the DC fan at this point ? since the output switches are SSRs.

Better to give the actual model # as opposed to "the one on the right".

The one on my right, clearly has mechanical relays and so the nearest thing they offer with SSRs, appears to be the "transistor" output.

See the table where the transistor-type has a "pulsed output"?
This is typically PWM. Hook the fan up to this, select a carrier frequency (I don't know the spec) and use the duty-cycle to vary the speed. A 24v fan will struggle to move at 50% but from 60% to 100%, you should have reasonable control.
If you ever feel like stepping into the 21st century, however..


Craig

 

[parky]

The one on the right is relay output not solid state the left one is transistor
The analogues are 0-10V input/output you will need a converter to drive the motor at variable speed i.e. convert 0-10v to 0-24v, however, a 24v DC motor will not provide ant tourque at low voltages or even run at some point.
also, the analogue outputs are not isolated so you have to be careful not to destroy them.

 

[eagl1]

Better to give the actual model # as opposed to "the one on the right".

The one on right, clearly has mechanical relays and so the nearest thing they offer with SSRs, appears to be the "transistor" output.

Yes, I mean the model FX3U-14MR which has relays. Because I want to control other AC outputs.

But my concern now is that how to control the speed of that 24V DC fan ?

 

[parky]

If you want to control the speed of the motor you will need to use the analogue outputs, however, you will need to have a DC motor controller with a 0-10v input for speed control, although they say it is an FX3U it is not exactly more like the older FX2N, the in-built analogues need to be accessed via a function called RD3A & WR3A, also the baudrate is usually fixed at 19200 for programming & unlike the FX range the PLC parameters cannot be written to.

 

[Tinine]

But my concern now is that how to control the speed of that 24V DC fan ?

Probably find lower cost on Aliexpress, but...




Craig

 

[eagl1]

The analogues are 0-10V input/output

You know what ! I should've really done some google search before posting this thread.

I typed the PLC model in google images and found this pinout diagram:

So there are 2 pins to provide a PWM or DAC signal. OK, that's pretty much what I need to know.

you will need a converter to drive the motor at variable speed i.e. convert 0-10v to 0-24v

How about using a simple MOSFET circuit to drive the fan ?

motor will not provide ant tourque at low voltages or even run at some point.

OK, so you mean the motor should run at rated voltage with enough current to start moving. Am I right ?

the analogue outputs are not isolated so you have to be careful not to destroy them.

Thanks for the information.

 

[parky]

No PWM especially on the relay model, some transistor outputs will allow a sort of PWM but I doubt the clone will be able to use that instruction only the real FX3 is capable I suspect, there are a number of differences between the real Fx range & these clones. A friend of mine has one I will ask him to try it on the transistor output model to see if it works, so it may be possible to use PWM function with transistor outpus but not on the relay one.

 

[I_Automation]

You could use the bank of outputs in sort of a crude way.

First use the first output, then run the power through 5 power resistors of equal resistance so it goes at the slowest speed you want.


Use the next 5 outputs to each bypass one more resistor.


Y0 + 5 resistors = CREEP
Y1 + 4 resistors = SLOW
Y2 + 3 resistors = MEDIUM
Y3 + 2 resistors = MED HIGH
Y4 + 1 resistor = HIGH
Y5 + 0 resistors = HI HIGH


If you turn more than one input on at the same time the higher speed will prevail.



If you don't need 6 speeds reduce the outputs and increase the resistors value.


EDIT: Rethinking this there should be one more resistor going to DC COM so this works as a proper voltage divider, but then I'm thinking it should be relay outputs and take the divided voltage INTO each relay and go out the COM to the motor

 

[Tinine]

You could use the bank of outputs in sort of a crude way.

First use the first output, then run the power through 5 power resistors of equal resistance so it goes at the slowest speed you want.


Use the next 5 outputs to each bypass one more resistor.


Y0 + 5 resistors = CREEP
Y1 + 4 resistors = SLOW
Y2 + 3 resistors = MEDIUM
Y3 + 2 resistors = MED HIGH
Y4 + 1 resistor = HIGH
Y5 + 0 resistors = HI HIGH


If you turn more than one input on at the same time the higher speed will prevail.



If you don't need 6 speeds reduce the outputs and increase the resistors value.


EDIT: Rethinking this there should be one more resistor going to DC COM so this works as a proper voltage divider, but then I'm thinking it should be relay outputs and take the divided voltage INTO each relay and go out the COM to the motor

I assumed that the reason for wanting to reduce fan speed was to reduce power consumption which won't be the case with the resistors.


Craig

 

[I_Automation]

I assumed that the reason for wanting to reduce fan speed was to reduce power consumption which won't be the case with the resistors

and want to connect a 24V/0.2A DC fan to the output.

Reducing a 4.8 watt motor power consumption?


Unless this is running off a bank of D alkaline batteries that reduction isn't going to make a $0.01 reduction on the annual electric bill from what a 24V power supply would use.

 

[parky]

expanding on TInine's idea you could use a 1R,2R ladder network for example 6 outputs equates to 63 speeds.
See here:
https://en.wikipedia.org/wiki/Resistor_ladder#Analog-to-digital_conversion
or here

https://www.best-microcontroller-projects.com/R-2R-ladder.html?utm_content=cmp-true

 

[Tinine]

expanding on TInine's

Not me, I'm a PWM-er





Craig

 

[parky]

So am I but from the posts it looks like the OP is using a relay output plc so the PWM instruction does not work.

 

[Tinine]

So am I but from the posts it looks like the OP is using a relay output plc so the PWM instruction does not work.

I would've gone with the transistor outputs and where required, drive external relays via transistor.


Craig