Shop OBEX P1 Docs P2 Docs Learn Events
Switching 12V 1.6A valve (need ciruit checked) — Parallax Forums

Switching 12V 1.6A valve (need ciruit checked)

computer guycomputer guy Posts: 1,113
edited 2010-03-24 12:30 in Propeller 1
Hi everyone,

Can someone please check this circuit and let me know if it will switch a water valve 12V DC (1.6 A)

attachment.php?attachmentid=67578


Thank you smile.gif

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"powered by Propeller" domed stickers $1.50 - Find them here
Check out my Design and Technology project for my Higher School Certificate www.ecosureblog.net
bmp
bmp
valve switch.bmp
527K

Comments

  • mikestefoymikestefoy Posts: 84
    edited 2010-02-09 10:01
    the circuit is fine, except for component values.

    R1 is too low, try 10K or greater ( unless you are switching at > 100Hz)

    the mosfet wont do.

    the VGS max for turn on is 4 volts, so a prop delivering 3.3volts wont turn on the mosfet.

    Also an IRF540N is rated at 33Amps, so its totally overkill.


    select a mosfet with a vgs max of 2 volts, and a continuous current of say 3 Amps.

    the FDT439N is 90Cents, but its SOT-223.

    http://www.fairchildsemi.com/pf/FD/FDT439N.html


    this one FQP13N06L is TO220, and only 46Cents, but the worst case vgs turn on is 2.5volts @250uAmps, leaving only 3.3-2.5=0.8volts to really turn it on.

    if its just a one of project, it will probably be OK, since its typical vgs turn on is about 1.8volts

    http://www.fairchildsemi.com/pf/FQ/FQPF13N06L.html




    Mike
  • computer guycomputer guy Posts: 1,113
    edited 2010-02-09 11:01
    Thank you Mike smile.gif

    So this should work?

    attachment.php?attachmentid=67582

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "powered by Propeller" domed stickers $1.50 - Find them here
    Check out my Design and Technology project for my Higher School Certificate www.ecosureblog.net
    valve switch.png
    439 x 409 - 4K
  • mikestefoymikestefoy Posts: 84
    edited 2010-02-09 11:21
    yes, looks fine to me.

    mouser.com has the FQP13N06L for $0.825



    Mike
  • computer guycomputer guy Posts: 1,113
    edited 2010-02-09 11:28
    and wiring up an LED to the gate with a 100ohm resistor in series won't interfere?

    Thank you smile.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "powered by Propeller" domed stickers $1.50 - Find them here
    Check out my Design and Technology project for my Higher School Certificate www.ecosureblog.net
  • mikestefoymikestefoy Posts: 84
    edited 2010-02-09 12:10
    wont be a problem, but why not put the led/resistor across the valve outputs ?, use a bigger resistor of course.

    i assume you are driving the led with about 10mA, so better on the output.

    I also assume you have only one or two valves, otherwise 10mA/pin from the prop could cause a problem if you drive the leds from prop pins.

    Also, driving the led from the prop pin will reduce its Voh, so reduce the mosfet gate drive.

    better put the led across the valve
  • computer guycomputer guy Posts: 1,113
    edited 2010-02-09 21:26
    Only driving one valve.

    Will put the led accross the valve.


    Thank you Mike smile.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "powered by Propeller" domed stickers $1.50 - Find them here
    Check out my Design and Technology project for my Higher School Certificate www.ecosureblog.net
  • computer guycomputer guy Posts: 1,113
    edited 2010-02-10 01:46
    Will a 1M length of 4 core phone cable between the propeller output and the circuit cause any problems.
    I am assuming that it will cause a drop in voltage by the time it gets to the circuit.

    In this case should I boost the prop output with a transistor before going to the cable?


    Thank you smile.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "powered by Propeller" domed stickers $1.50 - Find them here
    Check out my Design and Technology project for my Higher School Certificate www.ecosureblog.net
  • mikestefoymikestefoy Posts: 84
    edited 2010-02-10 07:23
    its better to put the mosfet near the prop, and then cable to the valve.

    I will assume that you are only turning the valve on and off, not pwm'ing it.

    If you must put the mosfet 1metre away from the prop, i suggest you put 2 off 1K resistors in series with the prop pin, and a 0.1uF capacitor down to 0 volts of the prop.

    Also raise your R1 from 10K to 47K

    this will act as a low pass filter to kill any noise being fed into the prop



    prop
    1K resistor
    1K resistor
    mosfet gate
    |
    |
    0.1uF capacitor
    |
    |
    GND (0volts)
    mosfet source
  • mikestefoymikestefoy Posts: 84
    edited 2010-02-10 07:32
    my simple schematic got screwed.

    put the 2 resistor, 1 capacitor pi filter close to the prop, and then run the cable to the mosfet, with R1 47K on the mosfet
  • computer guycomputer guy Posts: 1,113
    edited 2010-03-24 09:30
    Thank you Mike smile.gif

    I am still not quite sure how to wire up the led. I am assuming I put it in parallel to the diode with a 560ohm resistor in series.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "powered by Propeller" domed stickers $1.50 - Find them here
    Check out my Design and Technology project for my Higher School Certificate www.ecosureblog.net

    The Sarah Myatt Fund - Help Sarah and Her Family Fight Quadriplegia HERE
  • mikestefoymikestefoy Posts: 84
    edited 2010-03-24 12:30
    yes, put a LED +series resistor across the diode ( and thus the valve).

    the resistor value should be calculated so that between5 and 10mA is flowing through the led, so (12V-3V for the led)=9volts/10mA=1Kohms.

    Mike
Sign In or Register to comment.