Hi,

I will start off by saying I know next to little about electronics so bear that in mind if answering me, you may need to dumb it down a little (or a lot actually).

I currently have a DAQ controlled by labview running a motor through what looks like a couple of power transistors and a variable speed drive. This circuit and wiring was done by someone else outwith the company and actually operates as required. What I am trying to do is add another very small motor to the DAQ and have that run independently from the original larger motor. I have managed to cobble together some labview code to achieve this and I can get the correct output from the DAQ on the analogue output channel that I want. However the problem comes when I connect my motor, the motor does not turn and the voltage supply disappears. I am guessing that because the DAQ can't supply current (just a voltage) then when I connect the motor it just sucks all power leaving nothing.

Therefore I am guessing I am needing some sort of current amplifier or similar. I have done a bit of digging and I reckon I probably need a non inverting op amp, and I think either one that boosts the current (current feedback op amp?) or one that uses another larger power supply and steals current from it whilst keeping the voltage the same (Power op amp?). Please correct me at this stage if I am going off on a wrong tangent or misunderstanding the application of these op amps.

If I am correct above I could really do with a help specifying the correct op amp and coming up with a circuit that will work. I would also really appreciate some guidance on how to create said circuit, i.e. do I need a breadboard or do I have to get a circuit board printed and how do I do that?

The DAQ I have is a NI USB-6211 and the motor I am trying to run is this one ( http://uk.rs-online.com/web/p/positive-displacement-pumps/7026898/[URL='http://uk.rs-online.com/web/p/positive-displacement-pumps/7026898/)I'])[/URL]
I also have a 24V supply within the existing box that I can use.

Thanks in advance.

Mike

 

hi mos.
The extra motor requires only ~ 100mA at 5v
What is the specification of the DAQ output current and voltage.
BTW: don't put your link in brackets, RS cannot find the item.
E
http://uk.rs-online.com/web/p/positive-displacement-pumps/7026898/
Found the DAQ d/s, so we need details of the existing motor that works OK.

 

Hi Eric, thanks for the response.
Ah ok sorry about the brackets!

Yeah that's why I thought I would just be able to plug and play (I never thought to check the DAQ specs).
The specification for the DAQ states for analogue output the output current drive (if that's the right thing) is 2mA.
Have attached the specifications for the DAQ.

Thanks,
mos

 

hi mos,
look on the existing motor , there should be info printed on it.??
E

 

Thanks E, the last page didn't display all your message.

The existing motor is an AEG AM63Z AA2
Details as follows.
50Hz - 0.18kW - 230V(1.1A) - 400V(0.65A)
60HZ - 0.21kW - 265V(1.1A) - 400(0.65A)

But as I say that is not run directly from the DAQ.

mos

 

This is the DAQ you have. The analog output drive current is only 2 mA. If you are trying to drive a motor, even a small motor you will need something between the DAQ and motor to drive the motor. A simple drawing of what you have would help.

Ron

 

hi,
The DAQ cannot drive the small 5V 100mA motor directly, you will need a amplifier.
The drive to the existing motor is well in excess of what the pump motor could handle.

E

 

Thanks E, that was what I thought, but I'm not sure where to begin specifying the amplifier or how to wire it up.

 

Reloadron, I'm not sure a drawing of what I have will help.
1. my drawing of electrical circuits would be a disaster!!
2. this will be a completely separate circuit just using the same DAQ.

 

How do you plan to drive the added motor? Using an Analog Out or Digital out? Will the motor be run at just a single speed or variable speed using PWM for example? That will determine the Motor Driver you want to choose. That and the current needed for the added motor.

Ron

 

Thanks Ron,

My thought was to drive it from an analogue out, I have a code already that takes in a waveform and outputs a voltage, for this motor I would probably just set a straight waveform at a desired voltage so it gave a constant voltage out but with the option of changing it at any time. The data sheet for the new motor states a current of 0.19A.

 

hi,
Will the 'old' motor drive still be connected to the DAQ output at the same time as the new motor.??
That could be a problem.

EDIT:
Look at page #11 of this PDF.
Assuming that the existing motor driver is not connected.

 

sorry had to wait to post.
hi, yes it will be running simultaneous. The old motor will be connected to analogue out 1 and the new motor connected to analogue out 2.

 

I guess you know that a simple DC voltage output into an amplifier, powered from +5V, will run the motor at full speed.?
Reducing the voltage to the motor will slow it, but it will lose torque.

To achieve speed control PWM is used, [pulse width modulation].
To set a predetermined motor speed the DAQ would have to output a known PWM signal into the motor amplifier.

E

 

hi,
A simple circuit like this would give On/Off control of the pump motor.

 

Thanks E, I was aware of PWM but wasn't thinking I would need it. Ok so I have two problems, I can work at getting a PWM signal out of the DAQ but I still have the issue with the amplifier.

Thanks for the circuit diagram but I am struggling to understand it. Is this for use with PWM or not?

 

hi,
It will work with PWM, providing the PWM voltage level swings from say 0V to +5V.
Its a FET , so it will not load the DAQ output


EDIT:
For example,
Ignore the 3 left side devices, they generate a PWM for testing.

Have you chosen a base frequency for your PWM signal.?

 

Hi,

Its a FET , so it will not load the DAQ output

Could you expand on this please, bearing in mind my limited knowledge.
Thanks

No I haven't chosen a base frequency. I will have to look into PWM as I don't have previous experience.

 

Could you expand on this please, bearing in mind my limited knowledge.

The DAQ Digital output has a high/low current limit of ~6mA, the FET Gate current will be lower.

 

Thanks E.

Just to check I am understanding this.
The connection at the bottom with the red arrow is the connection that would go to the positive terminal of the motor?
The 5V on that diagram (next to V2), is that a separate 5V power supply separate from the DAQ? (If so I don't have another 5V supply I only have a 24V supply)