DC motor control

[AndrewEngEET]

I am in a research and development environment. I, as the junior engineer, have been charged with running a small 12v DC electric vacuum pump project.

I need to be able to control the speed (and voltage) of the motor, no matter what the load. The motor draws 15A normally, and can draw a maximum of 27 amps at stall. I am using a 15V supply capable of 60A, and want to supply the motor with between 10 and 14 volts, depending on the test requirement.

I spoke with Leeson Canada, and they suggested CAT number 175291, but it needs an external control (pot or Vcc). I am sort of looking for an all-digital unit.

Any advice? Thanks for your time. Long time sandy-bagger..finally registered!

andrew

 

[gcaudill]

Look for a DC motor controller with a kepyad for entering speed. A such equipped drive will usually also have a serial interface.

 

[blacksea]

I hope that full digital controller with build-in driver Cello-15/60 (Elmo -

http://www.elmomc.com)

with min voltage 10VDc and cont.current 15A is exactly that you need.

 

[BENHILL]

There are always a number of ways to skin the problematic cat.

How do you know that your digital interface does not hide an analogue control internaly? If it did, would it matter? Why, specificaly, are you looking for a 'an all-digital unit'?

Sorry for the questions, just trying to get a handle on your problem.

Ben.

 

[AndrewEngEET]

I'm not specifially looking for a digital unit. I just need any type of DC controller that will limit the voltage seen at the motor input terminals to a certain value. It does not matter if I have to use a multi-meter to help set up the value, because it will only change every few months. I just need something that is reliable and will not drift from the set level, no matter what the current draw between 0-27.5 amps.

Thanks,

andrew

 

[BENHILL]

So, is it that you want a linear output, where the exact linear motor terminal voltage level at variouse load values can be measured?

Or a pwm output, where the effective terminal voltage is derived from the ratio of mark to space of the 14V DC pulse train supplied to your motor?

Is the system expected to be open or closed loop?

Sorry, more questions, I have seen & absorbed what you have said above.

It sounds like a 'life test' rig for these motors. Further, that a fully linear response, & linear voltage level is expected as the output of the driver. You additionaly want the driver to cope with between zero current output to fractionaly over the full motor stall current of twenty seven Amps or so with no variation of the set output voltage, nor should that voltage to be prone to drift over times measured in months.

Let me know how close I am the your brief.

Ben.

 

[AndrewEngEET]

I am trying to simulate the motor running on a vehicle, so the PWM is not really the answer. This system will be open loop.

You are right about this being a "life test" rig. We are testing for extended periods (weeks) with the motor cycling on a relay.

And you are also right about the current requirements.

andrew

 

[Barry1961]

Could you use a linear DC power supply instead of a motor controller? It sounds like this would be closer to the actual conditions.

Barry1961

 

[BENHILL]

Precisely my own thoughts Barry1961. The power requirement is just shy of 400W for the worst case situation. So, a good precision linear psu of 500W or more with remote sense, adjustable output & foldback could be exactly what Andrew is looking for (it would be if it were my problem).

I don't know what his budget is, but there are units on the market with digital control. Keithley, Agilent/Hp, National all do bus controlled product (RS232, 422, 485 or HPIB & all of its clones).

A quick look on Google under "precision linear power supply" could be his best bet.

Ben.

 

[AndrewEngEET]

Thanks for the advice. I investigated some of the BK Precision models, and they seem to be perfrct for this application. Much chaper then I thought. (Around the same as the Leeson DC-DC controller)

Andrew

 

[BENHILL]

Andrew,

Glad we have been of some help to you. I have a background in automotive electronics, test equipment design, PSUs & motor control.

Your application intrigues me, in most vehicle apps weight & power conservation is of significant concern to the manufacturer.

Consequently, they are tending towards PWM to drive & position motors (also, they are tending towards using BLDC motors, which require a sequence of DC pulses to drive them).

Taking motor drive out of the linear domain leads to lightweight, high efficiency drives (usually with enhanced reliability). They are also cheap in mass production & automotive manufacturers do like cheap :~)

Anyway, I doubt that there is much you can tell us company confidential, I expect, but interesting nevertheless.

Good luck with your project,

Ben.

 

[twarr1]

Contact Polyspede Electronics

http://www.polyspede.com

and ask them about the new Sprint DIN rail mountable drive. I believe it is the perfect solution.