Controlling micro-pumps via PWM

Discussion in 'The Projects Forum' started by SoulBlade, Sep 17, 2012.

  1. SoulBlade

    Thread Starter Member

    Sep 17, 2012
    37
    0
    Hello,
    Hi, i'm working on a small project to operate two separate micro-pumps ( these kind: https://www.biochemfluidics.com/cart/store/comersus_listItems.asp?idCategory=85&Cur= ) via the MSP430F6338 using PWM.
    Each pump is rated 12V, 320mA (.i.e. 4W ), and operate by PWM (with a max. cycle rate of 2Hz). It's maximum current was not stated in the specsheet, so i'm assuming the 320mA given would be it's holding current.

    I'm using a MSP430F6638 controller whose pins are connected to two separate inputs of the ULN2803A darlington array transistor (it's peak output current on one pin is 500mA), the transistor does the switching via PWM from the controller.

    I intend to power the pumps with an LDO ( http://www.linear.com/product/LT3029 ) , i figured that since the outputs of the LDO are adjustable, i should be able to get 12V at 320mA from them with V(in) coming from a 12Vdc wall-plugin
    ( or alternatively just put a 36ohms resistor in series with the solenoid to achieve the 320mA .i.e 12V / 36oms = ~333mA)

    I wanted to clarify if this above configurations are valid ??

    Thanks for replies in advance.
     
  2. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    These are spring return solenoid run diaphragm pumps, measure the DC resistance of the coil that will give you something to work with as far as choosing a proper power source goes. If you can list that value there's something to work with, the stated specs you listed aren't useful unless we know under what condition those values are valid.
     
  3. SoulBlade

    Thread Starter Member

    Sep 17, 2012
    37
    0
    Given that the DCR of the coil isn't stated in the specsheet, that would imply i have to purchase the pumps to find it out ??
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    12v 320mA gives you a rough idea of the ohms using;
    R = E/I
    R = 12/0.320
    R = 37.5 ohm (approx)

    I would just start with the 12v supply and pulse that. It's a good idea using a voltage regulator as it will give you some stability in controlling the pump with your pulse width or PWM etc.
     
  5. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    If you don't have a pump to test you could always e-mail them and ask for the coil resistance specifically. It's probably safe as RB said to use the nominal value of 37.5 which as he said is fine to connect directly to 12V without a ballast resistor.

    My only concern is if that current is RMS at a specific frequency/duty cycle in which case the peak current could be significantly higher. It's not stated how it was measured and I tend to err on the side of caution with loose specs.

    As long as the pump meets your flow needs you can figure out exactly how to drive it when you get it. I don't think the regulator is really needed as long as you can be sure the highest voltage won't hurt the solenoid and you're not running very close to it's maximum flow rate, a lower voltage (to a certain degree) will only cause the maximum cycle time to be a bit longer, it just has to be high enough to pull the spring back (may take longer etc..)

    One important thing to take a look at is the MTBF stroke rating and the stroke rate you intend to use on average over time. It won't do you much good if the module fails in 6 months if you need it to last 2 years in your application.
     
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