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plc pwm driver to control dc motor

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I want to control dc motor 24 v 11 A using plc . so i need a driver circuit that is able to work on 24 volt pwm from the plc. what are your suggestions?
 

If you do not want to reverse the motor, a simple transistor can do. Put the motor in the collector side and apply the PWM drive to the base. You can also use a FET.

Most likely you will also need a gate driver (for a FET) because the output of the PIC cannot drive a power transistor directly.

You also need to have a diode-capacitor snubber. A 250W motor is mostly inductive load. Do you also need a brake function?

There are dedicated IC devoted for small DC motors (this one is not really small and is classified as fHP- franctional horsepower)

Start with a draft drawing of what YOU think is you need in your driver.
 

The question is if your PLC has a fast logic output with respective timer that is suitable to generate a PWM signal and what's the intended PWM frequency.
 

the intended frequency is 50 KHZ and my PLC can genereate up to 100 KHZ but what is the relation of this question to my question?
 

I don't think you should pulse 11 A on and off at 50khz...try a lower frequency. The motor inductance is so big that it wont need to be pwm'd at such a high frequency.
 

but what is the relation of this question to my question
Click to expand...
Feasibility. Your original question doesn't clarify that you have already checked. Apparently you did.

In this case I agree with c_mitra, use a MOSFET and a free-wheeling diode. Switching frequency should be optimized according to transistor switching losses, rotor magnetic losses, ripple current and acoustical noise.
 

I presume that the reason that you are driving dc motor by pwm'ing supply to it is because you recognise that this way of doing it gives less chance of stalling than by just reducing speed by reducing the constant dc voltage level to the motor.
 

Speed control of DC motors by effective reduction of the DC voltage is a well researched area and it ONLY works in a limited range. If you want very slow or very fast speed, you need to look elsewhere.

PWM control will give a range of 1:10 with reasonable torque. This is acceptable for most purposes, but for cars and locomotives, we need gears.
 

What kind of PLC are you using? And I agree with the others that 50 kHz is way too high. Remember that you need very clean and fast variable duty cycle pulses. The VFDs (Variable Frequency Drive) I've worked on used a 4 kHz base frequency.

Actually it's current that gives the torque, the voltage pushes the current.
 

ydtech said:
Actually it's current that gives the torque, the voltage pushes the current.
Click to expand...

Correct. because of the inductance in the motor winding, you will be pushing in little current in every pulse. Because of the inertia of the rotor, this is effectively same as operating the motor at a lower voltage. But VFDs are another kind of beast altogether. There the motor is essentially a 3 phase device and the speed is determined more by the frequency rather than the voltage. I guess 4 kHz VFDs are useful in the ultracentrifuges used for isotope separations. For industrial motors, VFDs are rated commonly upto 400 Hz.
 

I mean the PWM frequency is 4 kHz, the modulation frequency can be 60 Hz or whatever, even down to 0. With 3 synchronized bipolar outputs it's of course a bit more complex than what OP has in mind but the principle remains. PWM can take many forms.
 

Also, I take it that pwm'ing a high voltage to the dc motor means the current rise time in the coils is quicker. (as opposed to just using a lower equivalent average constant dc voltage)
 

ydtech said:
the modulation frequency can be 60 Hz or whatever, even down to 0.
Click to expand...

Zero modulation frequency on a VFD will certainly kill the motor. You can ramp the frequency for a soft start effect but ...

- - - Updated - - -

treez said:
Also, I take it that pwm'ing a high voltage to the dc motor means the current rise time in the coils is quicker. (as opposed to just using a lower equivalent average constant dc voltage)
Click to expand...

But the power delivered in both cases will be same (equivalent average constant dc voltage ensures that) and a 250W dc motor may start a bit faster but the effect may be hardly noticeable. What will be the benefits?
 

But the power delivered in both cases will be same (equivalent average constant dc voltage ensures that) and a 250W dc motor may start a bit faster but the effect may be hardly noticeable. What will be the benefits?
Click to expand...
...If you just use a lower dc voltage which on average is the same as the pwm'd one, then you may well stall the motor.
 

Zero modulation frequency on a VFD will certainly kill the motor. You can ramp the frequency for a soft start effect but ...
Click to expand...

VFDs are current sources and they limit it to whatever the motor can safely take. It's not very useful with squirrel cage motors, but permanent magnet motors will merrily stand still, locked at whatever position the currents determine. It takes a big wrench to move the axle a hair's width and with resolver feedback not even that,

- - - Updated - - -

If you just use a lower dc voltage which on average is the same as the pwm'd one, then you may well stall the motor.
Click to expand...

Which is where feedback control is useful. Be it a tachometer or a flow meter in case you're driving a pump.

But back to the chase. What PLC is the OP using, and how is the motor power regulated?
 

ydtech said:
But back to the chase. What PLC is the OP using, and how is the motor power regulated?
Click to expand...

But I have perhaps learnt more than the OP. His motor is 24V at 11A and I doubt PM motors come in large sizes. They are mostly useful in toys and small gadgets, right?
 

BLDC is a permanent magnet synchronous machine , available up to 10's of kw and beyond
 

In any drive control system is very important to know load type (torque profile vs speed) and main requirments (speed ramp, max speed, torque at zero speed, reverse or not and so on).
Brush DC motor have a cheap control logic and driver will be choose accordingly motor data, load and performance requiments.
VFD is used with asynchronous motor (induction motor) which a much more complex logic, from simple V/Hz to verctorial control (in this last mode, IM is "transformed" in a DC motor and may control it as a DC motor ... full torque at zero speed).
Most VFD are voltage source and for high power (beyond MW) most are current source.
So, more details needed.
 

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