# Current supply to a Micro-pump (DC motor)

Discussion in 'The Projects Forum' started by nikhilvastarey, Feb 10, 2009.

1. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
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Hello all
I have a BTC-IIS series Micro-pump from hargrave fluidics.
Anyways, it has been specified that @12VDC source, only on varying the current from 320mA to 350mA can i vary the output air-pressure of the pump.

http://www.hargravesfluidics.com/pdf/BTC-IIS/ST_D771-11_C.1F28G1.1F28N1.B12VDC_Rev_A.pdf

the above is the link to the data sheet.

So, basically what i have done is that i used a Variable voltage source @12VDC and connected the micro-pump across it. I am not getting the max rated pressure.
And as i change the voltage of the source, the pressure output of the pump changes but it is not matching the data-sheet specs.

So, my question lies in the fact that, should i convert the voltage source into a current source by connecting a resistor in series with the voltage source?

In the sense, the max pressure is achieved @ 16 psi @ 350mA (according to the sheet). So R=Voltage/Current ie 12V/350mA = 34.28 ohms.

so, if I connect a resistor of 34.28 ohms in seires with the voltage source, will I get a current source. btw, the resistance of the micro-pump (when it was OFF) is 12.6MΩ

Regards
Nikhil

2. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
7
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It has been mentioned in the data-sheet that the operating voltage of the pump is 12VDC and the pressure can be varied by varying the current!!!!

3. ### KMoffett AAC Fanatic!

Dec 19, 2007
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I think you guys are mis-interpreting the chart. You do not control flow/pressure by controlling the motor current. The motor current variation shown (Y-Right), when powered by a 12v source, is the "result of", not the "cause of" changes in the pneumatic flow/pressure load graphed (X).

Ken

4. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
7
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Then how do I get to control the pressure if that is the case.
I am able to get pressure variation when i change the voltage knob in the variable voltage source!!
But, the resulting pressure and the current being drawn from the voltage source do not match the ones in data-sheet.
The above logic is being used because cant the reverse be true??

Thank you all for the relplies.
Let the discussion continue.

5. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,584
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The chart only is valid for a 12v source, and shows the pressure (and current) varying with various flow rates. Yes, you will lower the peak available pressure by lowering the voltage, but you are also lowering the motor torque. If you really want to regulate the pressure, you need to run the motor at 12v, and add a mechanical or elecrotmechanical "pressure regulator" on the pump's output.

Ken

Ken

6. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
7
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yeah. that sounds good. so, what you are trying to say is that the current graph (Y axis) is the result of it. so, what is the point of the current graph. how was the measurement made?

In the sense, is the pump supposed to work along with a pressure regulator, and when the current is measured across that, the current graph follows that pattern is it??

7. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,584
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The current graph tells you that there is "little variation" in current between max-flow/min-pressure and zero-flow/max-pressure. So, motor current is almost independent on the Flow/Pressure...at 12V. The graph is created by controlling the flow and measuring the pressure, or controlling the pressure differential and measuring the flow. The current plot is pretty unimportant.

Ken

8. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
7
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I just found about this L293D chip from SGS Thomson. This chip is used to control the DC motor. Whats even more, i found this L293D motor control KIT from Solarbotics.
http://www.solarbotics.com/products/k_smd/resources/

I am really confused now. This Kit looks really promising, but it talks more about robotics. Will, it work for DC motor too?

And yeah, obviously, i need Computer control, preferably through LabView!!

9. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,584
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nikhilvastarey,

The L293D is a dual, H-bridge, intended for the bi-directional control of one or two motors. Your pump runs in only one direction. It can be controlled with just one logic-level power MOSFET and a diode (flyback), from any NI digital output.

Ken

10. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
7
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Hello
I am not interested in using the NI devices

1. It is expensive
2. I had in my mind to use the USB 6008 DAQ from NI which gives out 0-5V analog but I need to use a fair amount of circuitry to amplify the voltage and current.
The above reasons resulted in me choosing that other device.
can i use the pump with that device???

11. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
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The "other device" is a \$13 kit with \$3 worth of parts in it. And as KMoffett has already noted, it is more complicated than you require. All you need is a one dollar logic level power MOSFET and a five cent diode. (And a PW modulated input, of course. But you would need such with the "other device" as well.)

12. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,584
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I didn't see the op make reference to using PWM. If there was an intent to PWM that to control output pressure of a diaphragm pump, it think they will be very disappointed with the results.

Ken

13. ### Bernard AAC Fanatic!

Aug 7, 2008
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We know a lot about the pump now , but what is the end result that you are looking for? With a flexable outlet line and a pinch clamp you have full control of pressure. If you wish to control pressure electronically,pinch off output to 16 psi @ 12 V, then you can control pressure 0-16 psi by varing motor voltage, 0-12V.

14. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,584
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Bernard,

Has the OP, or anyone, talked to Parker about trying to realistically control the pressure by varying the motor supply voltage?

Ken

15. ### Bernard AAC Fanatic!

Aug 7, 2008
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Page 1, Tried varible voltage supply.

16. ### KMoffett AAC Fanatic!

Dec 19, 2007
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Yup! Forgot that. And the OP said that the pressure changed, but didn't follow the chart. That's because the chart is Flow vs. Pressure at a fixed supply voltage of 12V. I think in the end the OP will find that trying to control the pressure by changing the pump voltage will be like trying to control the speed of a car by dragging your foot...it might work, but not well.

Ken

17. ### nikhilvastarey Thread Starter New Member

Feb 10, 2009
7
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Hello all
sorry for the terribly late reply.
1. relating to the variable voltage pressure control, I have been adviced by the hargraves AE that, at no point of time should the motor stall due to low voltage. If that happens, then the possiblilty of the brushes getting damaged will occur. So, I was strolngly adviced against that.
But, if the motor is controlled within the range of 5V to 12V, motor stalling will not occur, because the min voltage for the motor to stall is about 4V. But, at 5V or so, the motor chugs along, sounds like a steam engine. A fair amount of pulsation occurs resulting in a non-constant pressure suply. In the sense, the air is pulsated. (but that should be of any concern at the moment)
2. PWM technique. This looks like the most favoured at the moment. As, the pump will remain connected to the 12V source while the digital pulses will do all the work.
This bubble, was also bursted by the hargrave App Engg, as he mentioned that speed is not the only factor for the change in pressure. He mentioned about the chamber, brushes and so on. So, basically, on varying the speed of the pump, we must not expect a precise control of pressure.

His solution:
the better way to solve the issue, he said, is to use a bleed valve. bleed out the excess air, vary the air into the working channed, thus varying the pressure. his way, is the valve way.

My need: Even though using the valve seems like the industrial norm, my need lies in the fact that I need a miniaturized system Due to which, I have opted to the electronics way out.

After some thinking, I have decided that i would go for the voltage control, but between 5V and 12V. Can that be done using the LM317 chip, or some sort of NI USB module (which is expensive, so tha would be my last resort).

Please keep in mind that, I would like to have computer control over all these operations. In the sense, vary the voltage of the pump through a user interface.

So, the other issue arises : computer interface of the pump which has to be voltage controlled between 5V to 12V.
phew
Sorry all for the late reply

All the respects for the gurus
Best regards
Nikhil

Dec 19, 2007
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