Basic question. I want to drive an old Pittman Brushed DC (PMDC) motor from Labview using an Analog Out for a controls education lab. I can spin the motor fine from a lab power supply. I want to close the loop in Labview software. Obviously the Analog Out cannot supply enough current so I’ll need a power Amplifier between the AO and the PMDC. I cannot find one of these anywhere. EVERYTHING is PWM motor controllers. What options do I have? It seems like I need something crazy simple. Vin=Vout with a boost in current. That is all. Thanks for the Help
Depending on the motor you might get away with a voltage regulator as a DC source, controlled by your Analog Out. You might also find a power op-amp that’ll work. What are the motor specs for voltage, current, coil resistance, etc ?
The motor is quite a good size. It can spin a 2in steel shaft with ease. I am not really an electric so I would love something off the self. So when you say a Voltage Regulator as a DC source, what do you mean?
On the bigger picture maybe you can educate me on some things.
1.) why is my application so hard to find a solution to? I’ve asked dozens of people and no one seems to know. I can spin this motor with a lab power supply 0-10V because it has the power behind it. I want to do the same thing but with a DAQ 0-10V but I need to add the power (current) behind it. Doesn’t that seem simple? Or am I crazy?
2.) why are all of these PMDC controlled with PWM not DC voltage 0-10? I’m trying to have this educational DC Motor Lab where some of the motor parameters are found but I need a consistent Voltage In for the standard models to work. Is it possible to use the COTS PWM equipment and still know this Voltage In to the PMDC? If so then I don’t need a power amp and I can use the PWM options but still “back out” the voltage to the motor.
jrkeme:
1.) why is my application so hard to find a solution to? I’ve asked dozens of people and no one seems to know. I can spin this motor with a lab power supply 0-10V because it has the power behind it. I want to do the same thing but with a DAQ 0-10V but I need to add the power (current) behind it. Doesn’t that seem simple? Or am I crazy?
I don't recall many times in my career where a high current variable "DC" voltage is used. There are power op-amps for this. You may be able to use one if you can tell me what current the motor will draw.
jrkeme:
2.) why are all of these PMDC controlled with PWM not DC voltage 0-10? I’m trying to have this educational DC Motor Lab where some of the motor parameters are found but I need a consistent Voltage In for the standard models to work. Is it possible to use the COTS PWM equipment and still know this Voltage In to the PMDC? If so then I don’t need a power amp and I can use the PWM options but still “back out” the voltage to the motor.
PWM is used because it works and it's cheap to implement. You can certainly measure the effective DC voltage delivered to the motor via a PWM'ed signal. You just need to implement a low pass filter to remove the AC "noise" and input the resulting voltage into a DC DVM.
thank you for the response. I think I’ll be ok with PWM now that I know more about it. We had an old Power Amp back in my college days that was about the size of a toaster that just boosted an input signal in current only and kept voltage the same. I figured that was how it always works. I’m learning that no one does that and only uses PWM. What is an easy way to design the roll off frequency for the low pass filter of the PWM. I’m not moving things that fast 10s of hz max.