# DC Servo Drive



## John252058 (Jul 24, 2014)

Any suggestions to control a 2.2 kw dc servo motor for variable speed on the cheap


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## John Hasler (Jul 24, 2014)

John252058 said:


> Any suggestions to control a 2.2 kw dc servo motor for variable speed on the cheap



An Arduino, an optical interrupter, a homemade interrupter disk, and a handful of IGBTs.


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## DMS (Jul 24, 2014)

How cheap is "on the cheap"? Also, are we talking brushless DC servo, or brushed DC? For a brushed motors, drivers are not to bad to purchase, for example, the Gecko 320X is only about $120 USD

http://www.geckodrive.com/geckodrive-brush-dc-drives.html

These are what I run. They won't run the drive at full capacity, but they will do up to 1.6kW (80V @ 20A). For a larger driver these will go up to 5.6kW

http://www.automationtechnologiesin...ervo-motor-driver/dc-servo-driver-dg4s-016035

Now, John is right, you could build your own, but it is unlikely to be cheaper. I took this route on some stepper motor drivers a while back. I learned a TON, but after all was said and done I probably payed 2x what I would have by just buying an off the shelf driver.

If it is a brushless DC servo, I have heard some VFDs will run them, alternatively, start trolling E-bay.


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## JimDawson (Jul 24, 2014)

DMS said:


> If it is a brushless DC servo, I have heard some VFDs will run them, alternatively, start trolling E-bay.




You are correct, a VFD will run a BLDC motor.  You just have to match up the voltage and power output capability.


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## LEEQ (Jul 24, 2014)

Are the vfd's specifically for dc motors? I'm going to have to look for threads on this. I would love to get the how to and nitty gritty. Does the programming of the drive need altered? I am very interested in all of this.


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## JimDawson (Jul 24, 2014)

LEEQ said:


> Are the vfd's specifically for dc motors? I'm going to have to look for threads on this. I would love to get the how to and nitty gritty. Does the programming of the drive need altered? I am very interested in all of this.



There is a big difference between a Brushed DC motor, and a Brushless DC motor, BLDC

A Brushed DC motor runs off of Direct Current, a Brushless DC motor is actually a 3 phase motor that has a permanent magnet rotor (armature).  A brushed DC motor will only run on Direct Current.  (no, we're not going to get in to universal motors here)

A DC motor may have a wound or a permanent magnet field.  There is a difference between a rotor and an armature, but for the purposes of this discussion, suffice it to say they perform the same function in the motor, they spin to run your machine.

Brushless DC motor controllers are supplied with Direct Current either by a battery or a DC power supply, depending on the application, then the controller outputs 3 Phase AC to the motor.

A *V*ariable *F*requency* D*rive is normally supplied with AC power, converts it to DC in the power supply section, which is then converted to a variable frequency, variable voltage, AC, 3 Phase output.

EDIT Corrected this sentence: "_A DC motor may have a wound or a permanent magnet *armature*"  (__armature should read *field*)_


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## John Hasler (Jul 24, 2014)

Originally "brushless DC motor" referred to the combination of a three-phase PM rotor motor and a simple controller, usually in an single package.  These devices were configured to behave just like DC motors with the electronics in the controller replacing the commutators.  Now the term is often used to refer to the motor alone when it is intended for BLDC-type applications.  The controllers are also often much more sophisticated than the old "electronic commutators".  This is confusing as there is nothing DC about these motors absent an appropriate controller (which can in some cases be a VFD).


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## hvontres (Jul 24, 2014)

I am running a 1.5 Kw Brushless Servo in my lathe off of a Hitachi WJ-200 drive. It works, but its a bit touchy. It seems the motor only likes to start reliably at lower speeds. If I turn the speed pot up too high, startup becomes hit and miss. If it doesn't catch, I need to reset the drive. Since the drive is running sensorless, I also have had issues with the motor getting out of phase with the drive and stalling out on heavyer cuts. On the upside, I do get quite a bit of speed range and I don't really need to worry too much about the motor overheating at lower speeds.


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