DC motor input voltage control (hardware advice)

[ATMA]

Hi all. I have a 48V 3A RS555 motor with an encoder mounted on the shaft so that it can be operated as a servo motor.

Normally this would require a servo driver but since closed-loop feedback control is not required with my application a typical DC motor driver would be sufficient? (the motor should run at max)

I've been searching for a hardware which allows a gradual ramp up of the voltage/current for the motor and simple to interface with my 6221 DAQ card. But search terms such as motor soft-starter has failed to yield any relevant results. All i get are hardware which runs on 230VAC and are way to huge for my application.

Ultimately i'm looking for something which would prevent me frying my motor during start-up and simple to control using the AO of my DAQ card. I have limited budget and i must not go wrong with my hardware thus i was hoping someone can have any suggestions on the hardware?

[GiGe]

HI ATMA,

Currently we don't sell any DC servo drives (We do sell one DC stepper motor drive).  But we have a list of Drives that we recommend.  Keep in mind that these drives are recommended to be used with our motion controllers.  I realize that you already have a DAQ card and that you are trying to keep your cost low, but using a motion controller would substantionally cut down on your development time. Especially since you are using a servo motor you should seriously consider using one of them.  Without a motion controller you are going to have to create your own PID control loop and even then it won't be as accurate if you are doing this in windows, if you are doing it on a real-time target then you can do it at the same speed if your code in your control loop can be executed in less than 250 microseconds.  But in either case you should make sure that the drive you purchase supplys the correct amount of current and inductance for your motor.  I hope this helps.

Regards,
GG

[AnalogKid2DigitalMan]

ATMA:

Can you post a link to a page that has technical information about the motor?

[Brian_Beal]

Are you just controlling speed, or direction also?  You could use a standard 90VDC drive, and just turn down the maximum speed pot to limit it to 45 volts.  You will be able to control speed or torque from your DAQ card using an analog ouput, but not both at the same time.  Keep in mind that with a PWM DC drive, the motor windings and motor leads will be seeing 160VDC spikes, but that should be OK for most motors.  Minarik is a good choice for DC drives.

[ATMA]

Hi guys, thanks for your replies. Sorry for my late reply as i was out a couple of days.

Thank Gige, as i mentioned i'm not looking to implement a closed loop control for my application as i only need to drive the motor in a controlled fashion. The objective is to run the motor at full mode, turn CW and CCW and that's it. The only thing is to control the ramp up current or voltage across the motor during the initial start-up.

Hi Analogkid, it uses a Mabuchi RS555 motor http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_555pcvc with an quadrature encoder attached to the shaft. It works in a servo motor fashion but it's not exactly a servo motor itself. My application is just to find a driver so that i can control the voltage and current to the motor during startup.

Thanks Brian, i'll check out Minarik. But 1 thing, when they say speed control for motors are they refering to current control? Because if i remembered correctly the speed of the motor is proportional to the current correct? If that's the case, if i want to prevent from frying my motor by applying the line voltage (48V) directly across the motor i should be looking for speed control drivers?

Message Edited by ATMA on 08-21-2007 11:11 PM

[Brian_Beal]

In a DC motor, current is proportional to torque, voltage is proportional to speed.  A standard DC drive will technically control both, but only works in one mode at a time.  If it is in speed mode, then the pot or analog input voltage sets the voltage output, and hence speed.  The drive will try to hold that voltage constant by adjusting current, up to the set current limit.  As the load increases, so will the current.

As long as your motor is a permanent magnet, brushed motor with 2 leads, then a simple DC drive will work.  If it doesn't have brushes, then you will need a brushless drive.

[AnalogKid2DigitalMan]

ATMA:

Your 1st post calls out a 48V 3A motor, but your link is for 9-30V and 12-32V at around 1.3A motors. Gotta love the wide range of applications for that motor

I found this from Dart Controls, it takes an analog input 0-10V to control speed and has a ramp up control, you may to look into it further. I never have used it.

http://www.dartcontrols.com/InternetConfig/Catalog/65ESeries.pdf

-AK2DM

[ATMA]

Thanks Brian for your explanation and Analogkid for your link.

Yeah, i know i posted at 48V but the link is a 12V motor. The motor is actually from our customer so i found the website through the labels on the motor itself. The manufacturer of the actual motor was not provided by the customer.