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Solenoid Problems — Parallax Forums

Solenoid Problems

hughgoodbodyhughgoodbody Posts: 1
edited 2005-01-10 00:26 in BASIC Stamp
Can anyone help me out? I am operating a proportional solenoid valve and a solenoid pump from a Stamp via two seperate MOSFETS. The valve is operated using PWM and the Pump operated from a simple pulsing program. Both work great seperately but when they are both required to operate at the same time the pump works but each time it pulses it shuts down the valve. The power supply is of ample capacity. However if I power the pump via a relay and seperate battery, everything is fine. Is there any way that both valve and pump can be operated from a single power source without the interference that I am getting?

An additional problem I have also encountered is I am triggering a piezoelectric igniter from another MOSFET. This creates a high voltage sparking ignition system. Each time it sparks though the electronics shut down. Can anyone suggest a suitable way of stopping this from happening? I assume it is to do with the high energy discharged to the ground plane.

I would be most greatful for any suggestions.

Many thanks

Comments

  • achilles03achilles03 Posts: 247
    edited 2005-01-06 16:34
    What is your power supply and what are the solenoids pulling at max capacity? Are you powering the solenoids with a battery? If so, one problem you might be having is that the internal resistance of the battery is increasing to the point that the voltage across the terminals drops significantly, and you're getting less power to the solenoids (even though you think the power supply is adequate). I've used small solenoids, which pulled about 5 Amps EACH (and those were SMALL!). So reconsider if your power supply is adequate.

    In regards to your igniter, it might be EMI created by the spark. Nearby leads and wires act as antennas and can have voltages induced in them which cause wacky things to happen. I had EMI from a single .5W radio nearby a modified camera, and the camera would start rewinding everytime the radio transmitted. That spark is inducing EMI MUCH greater than my .5W radio, but for a much shorter time. If this is the case, you may try to move the spark source further from the BS2 and nearby wires. Or you could try to shield the BS2 from the EMI with a faraday cage (or similar).

    If that doesn't help, it might be something related to the high discharge into the ground plane. You might try having a separate ground plane (using a standard 4-pin relay or something).

    Dave
  • ErnieErnie Posts: 20
    edited 2005-01-06 18:44
    If it is an EMI event (I'd call this one an EMP, ElectroMagnetic Pulse which is usually reserved for nuclear blasts) you would probably hear it as a CLICK on a nearby AM radio.

    More likely it's electrical, the solonoid and motor being inductive and storing energy they then dump into the power supply upsetting the Stamp. For a MOSFET controlling a pump, motor, or relay you'll need some way to snub the energy stored in the inductance that wants to go SOMEWHERE when you turn off the MOSFET.

    Assuming your solonoid and motor connect to the positive supply, other end to MOSFET and thru that to return, you could connect a diode across the solonoid/motor, with the cathode (banded end) to positive. The diode should be of some rugged type, such as a 1N4003 (available at Radio Shack if you need it fast not cheap).

    If you already do this, post a schematic as it should help someone here see the problem.
  • achilles03achilles03 Posts: 247
    edited 2005-01-06 21:46
    The EMI/EMP event he mentioned was caused by the igniter system, not the solenoid or motor. That's a separate (but possibly related) issue.

    But now that you mention it, he did say the ignitor had a high voltage induced on it... might there be an inductor in there of some sorts? If so, you'd probably need a shunt diode like Ernie described in there... the induced backvoltage can be VERY high, which might be upsetting your electronics one way or the other.

    Dave
  • Alan BradfordAlan Bradford Posts: 172
    edited 2005-01-10 00:26
    HI,

    I run into this all the time. Plasma Torches start with a 10,000 to 15,000 2-5 MHZ spark. I fire them with Stamps all the time. I put Digital Noise Filters on All I/O, Power and Programming pins. I am on the road and do not know the part number off the top of my head. I get them from· Murata through Mouser Electronics. They look like a 3 legged Capacitor. the middle leg is gorund and the signal passes through the outside legs.

    When I leave the programming cable attached and fire the startor/ignitor it will lock up the Stamp instantly.

    I also use a mechanical relay through a SSR·to power the circuit as the one I use is a big bug Zapper HV tranformer. This is plenty of isolation.

    All other cables that are remotely close to the Ignitor NEED to be shielded. Connect the drain/shield wire to ground at one end only. Ths prevents ground loops and makes the system run more reliably.

    Thanks,

    Alan Bradford

    Plasma Technologies
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