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Converting 24vdc PWM to logic level for motor driver

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Congo_g

New Member
Hi, I have a PLC that I'm trying to send a PWM signal out to a DC motor driver for varying speed.

My PLC output signal is 24VDC sinking type and I vary the duty cycle from 0-100% over a pre-selected set frequency. I can connect a small DC motor directly and control speed nicely. But I have selected a motor driver for the larger DC motors I'm using now (4 full load amps)

The driver works well to start/stop/reverse the motor with its onboard push buttons. But not so well to control using the PWM input signal option.

The motor driver board accepts 0-0.7v(low) signal and 1.3-5.0v(high) signal levels. This is a problem because I cannot get the PLC control signal to work with this driver. I've tried opoisolators and IR520 MOSFETS but have had no success.

Can anyone explain the simplest way to circuit methods to convert these control signals?

Thanks
 

MaxHeadRoom78

Well-Known Member
Most Helpful Member
Is this a dedicated PWM module made for the PLC?
There is more info/make/circuitry needed on both pieces of equipment, otherwise it is pure guesswork?
Max.
.
 

MikeMl

Well-Known Member
Most Helpful Member
Is your PLC an "open-collector", current-sinking-only type output, or can it source current, too?

How do you reverse the motor? Are there two PLC outputs one of which goes high while the other goes low?
 

Congo_g

New Member
Thanks for the reply:
The PLC is a Nano-10 (by Triangle Research) and is only open collector on the 2 output available channels. These are fairly low cost and I/O limited.
The PWM module is not by the same manufacturer and is not specifically made for sure this PLC, so I'm trying to "make it work". The PWM board is a cytron MDD10A, dual channel PWM driver. It does have a forward/reverse signal input for each channel but all I'm interested in is speed control. There are forward/reverse buttons locally on the board for testing.
I'm guessing signal conversion from the PLC PWM output is possible but not sure how yet.
 

MikeMl

Well-Known Member
Most Helpful Member
Thanks for the reply:
The PLC is a Nano-10 (by Triangle Research) and is only open collector on the 2 output available channels. These are fairly low cost and I/O limited.
The PWM module is not by the same manufacturer and is not specifically made for sure this PLC, so I'm trying to "make it work". The PWM board is a cytron MDD10A, dual channel PWM driver. It does have a forward/reverse signal input for each channel but all I'm interested in is speed control. There are forward/reverse buttons locally on the board for testing.
I'm guessing signal conversion from the PLC PWM output is possible but not sure how yet.
Then it is dirt simple: connect a 4.7K pull-up resistor between the PLC output and a +5Vdc supply. The 0V end of the 5V supply is tied to the PLC ground. Also connect the same PLC output to the input of the PWM driver. The PWM driver ground must also be tied to the PLC ground.
 

MaxHeadRoom78

Well-Known Member
Most Helpful Member
Usually it is hard to interface anything other than simple logic I/O on a PLC or Smart Relay without the use of a specialty module for that PLC, the scan time can vary so much between output update times, it affects any thing close to a real time output.
Max.
 

Congo_g

New Member
That did work, and gives me good control to the PWM module, thanks very much. I used the available 5v signal, like you suggested, provided by the PLC for the pull-up resistor.
I'll have to adjust the PLC driver code because the signal acts inversely to the module output. When the PLC PWM output duty cycle increases the result is a decrease from the PWM board output, not too big of a deal and easily changed with code in the PLC block. I guess this effect is due to the sinking nature of my PLC output. I can live with that though.
 
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