Drive dc motor using NI ELVIS II DAQ

[tintin99]

Hi I would like to use NI ELVIS II Analog output pins to drive a DC motor. From the specification I think NI ELVIS II can supply just 5 mA while I need 0.2 A to drive this motor. I can also drive this motor using variable power supply pins on NI ELVIS II but I get nothing when I start to generate somthing in LabVIEW using DAQmx functions and AO 0 andO 1 pins. Would you please help me can I use NI ELVIS II DAQ to manualy generate DC voltage? 

[TSJim]

Hi,

The specifications for the variable power supply is: 0.5 V at 160 mA, 5 V at 275 mA, 12 V at 450 mA.   Assuming the connections are correct and the switch in front is not in 'manual' mode, it is right on the edge of the specifications.  I think I would try setting the voltage at 12V for about 300ms (assuming your motor is rated for this) and then immediately dropping it to 5V - motors usually need extra power on turn on to overcome stiction and I don't think you will do any damage to the PS if it doesn't work.  

If you are allowed to use a power transistor you could connect it to the +5V and use Pulse Width Modulation to control the speed of the motor.

Thanks,
Jim

[tintin99]

Hi Jim,

Mant thanks for your reply

Do u mean I can't use analoge output pins of the NI ELVIS II to drive this motor!  Unfortunately I can't use any power transistor. This DC motor is used to a rotate disc of an optosensor. I need to programmatically supply this DC motor using LabVIEW DAQmx blocks and NI ELVIS II. I have attached the spec form of this DC moto

 to this email. I would really appreciate if you have a look at it. 

[johnsold]

No.  You cannot run that motor (or any motor) from the Analog Output pins. The AO produces a voltage but cannot deliver a significant amount of power.

Your motor (assuming you have the 12 V version) requires 100 mA at no load, 300 mA at the "maximum efficiency" point, and perhaps as much a 1-1.5 A when stalled (not specified). Jim indicated that the ELVIS power supply could produce 12 V at 450 mA. I have never used ELVIS, so I cannot speak from experience, but the variable supply MIGHT be able to run your motor. It may depend on how much current the motor draws as it is starting up.

You should probably include a protective diode to avoid any damage to the power supply.

Lynn

[TSJim]

Hi,

Adding to Lynn's comments, the motor should work with the variable power supply if it is the 12V model.  The stall current is important - the motor will draw this for a short period of time when it first starts spinning.  If the stall current is over 450mA then the power supply may shut itself off for protection.  The stall current can be determined by measuring the resistance of the coils with a Digital Multimeter and dividing by the drive voltage.

The prefered way to control a motors speed is with PWM - using a power transistor and a power supply that can supply more than the stall current.  Controlling the speed of a DC motor by changing the voltage is unpredictable, at lower voltages the motor may just stall (stop spinning) and then the motor will draw a lot of current. 

good luck!

Jim