How to parallel many solenoid valves?

Discussion in 'The Projects Forum' started by snp-2010, Sep 15, 2013.

  1. snp-2010

    Thread Starter New Member

    Sep 10, 2013
    6
    1
    hi
    recently ,I've been working on a project in which i should parallel about 100 solenoid valves . but , there's a problem! when ever I try to turn on more than 5 valves together, my power supply turns off! i'm using a PC power supply and each solenoid needs 1 amp current to open and 0.3 amp to stay open and I'm using a (TIP122) to drive each solenoid valve.
    I know that the current that this power supply gives me is not enough for my project at all and also the voltage. but i can't find an easier and safer way than using these kind of power supplies. I specially shouldn't use 220V in this project because of safety issues and i couldn't find an ideal power supply and circuit for it. I need somebody's help on this issue...
    how can I make a power supply that can supply the power needed for this project?
    what's the circuit?
    what's the best way to parallel the solenoid valves?
    having said these ,I'm controlling these solenoids with an ATmega32 micro.
    you may help me?
    thank you
    :eek:
     
  2. #12

    Expert

    Nov 30, 2010
    16,246
    6,736
    I can see that trying to slap (100) 5V solenoids with 500 volts is dangerous. The other end of the spectrum is trying to throw 100 amps through 100 valves in parallel. Apparently you are trying to find the middle ground.

    First, tell what voltage each solenoid needs.
    Perhaps you can fire a 220V triac to turn on (5) 20 amp supplys.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    If using a PC power supply for the solenoids, what is the voltage?
    The 12v supply on a PC has MUCH lower current capability than the 5v.
    Solenoids generally start at 12V AC/DC.
    Do you have BEMF diodes across the coils?
    It most likely would have been more practical to use 24vdc solenoids.
    A simple isolation transformer and bridge is all that is needed for a solenoid supply, smoothing and exact regulation is not necessary for this application, as long as the current capability is there.
    By parallel I assume you mean across the same supply? Not all switched at once, surely?
    Max.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,979
    3,680
    What application do you have with 100 valves? Maybe a little background will help us find a solution to your problem or reframe the question.
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I'm guessing 3d water fall, or some sort farm/green house application.
     
  6. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,786
    Even if they can be scheduled just a little bit so that you can turn a few on and take the 1A/valve transient and then let that settle down to the 0.3A/valve hold current before turning on another set.

    Depending on the application, that might be unnoticeable or it might be completely out of the question. We really do need some context to work with.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    I am slightly confused if these are DC solenoids, why the high inrush and low steady state, There is no inductive reactance state to satisfy as in AC solenoids, on DC both states should be the condition of the DC resistance of the coil?
    The only situation I can envisage where the two conditions are different is if the supply is lowered once the solenoid is energized to take advantage of the higher efficiency of the field once pulled in?
    Max.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I'm less than 100% convinced of what I am about to say... I believe there is some factor to with the air gap. I was watching some thing about pinball solenoids recently, and they showed that the amp draw of the solenoid was greater when it was actually moving a load, and that in any case, once the solenoid is completely sucked in and there is no more air gap (replaced by high permeability core/plunger) the amp draw goes down even further.

    It is something that is on my unwritten list of things to research and understand further, but I have also noticed that a DC solenoid or relay will draw less current once actuated. I

    have also read about RC circuits used in combination with a MOSFETS or other switches to provide high switching current and then taper off to low holding current (current limited by resistor). A more proactive approach to ensure lower holding current - this might also be what OP is referring to, I don't know.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    The difference between an AC solenoid/relay and a DC version, is the AC has the edge Only at pull in time, this is due to the very low DC resistance of the coil causing an initial high current, this coupled with the pull in time until the inductive reactance takes effect = higher magnetic field, after this, there is a tendency for the armature to drop out as the AC crosses zero point, to offset the potential 'chatter', a shading or copper shorting ring is placed at some point in the coil, this causes a phase shift in this part of the coil and helps retain it through the zero cross.
    The DC version has the disadvantage that the current is restricted by the DC resistance of the coil, sufficient magnetic field has to be produced to attain the pull in
    and requires a greater current sufficient to attract the armature than retain it in position, technically once energized the voltage can be reduced in order to lower the current.
    Max.
     
  10. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Everything I'm reading about solenoids that mentions the air gap and switching current vs. holding current applies only to AC solenoids. It all agrees that current draw in DC solenoids is affected only by DC resistance of the coil, and that position of plunger doesn't matter. So I'm conceding for now, but I plan to test it out on the bench. I suppose I could be remembering things wrong about what I witnessed before with DC solenoids.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    Think of how would the effective resistance be Decreased in a DC coil circuit?
    Also you can actually watch the current ramp up with a 'scope on a large DC coil.
    **In an inductive circuit the current lags the voltage**.
    Max.
     
  12. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,786
    It wouldn't surprise me for the current draw to be somewhat different at startup and at holding just from an energy perspective. When you activate a relay, you are causing something to move and thus performing real work on it. So you have a transient event in which the relay coil as acting like a transformer and transfering energy to something else as well as dumping energy into its own field.

    Unfortunately, I lack the background in magnetic circuits to even begin to take the analysis further.
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I had the same thought, but can't back it up. I guess the energy, after moving the load, quickly changes it's focus to creating heat.
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,729
    759
    I believe it's like trying to drive a heavy duty motor tht could run on battery from a SMPS.
    The start up current would be like 200% more so tht the supply shuts down.

    Same thing is happening when u parallel so many solenoids. You could drive a few but inrush current is too much for ur supply.

    Some calculations and a linear supply is needed here.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    Not quite the same thing, a DC motor presents a very low resistance, bordering on a short circuit when full power is applied, as the motor increases in RPM, there is Generated EMF that opposes the applied voltage, this then reduces the current and the motor increases in RPM until the BEMF almost equals the applied voltage, at this point, current will be at minimum and from then on will depend on load, causing the rpm to drop and decrease the BEMF.
    With a DC solenoid, the full resistance of the coil is presented at switch on, and a solenoid does not have the armature fully within the coil, only when the magnetic field builds does the armature move over.
    Once energised, DC coils are more efficient and do not suffer the burn out possibility of AC coils where if the armature does not move over, or someone pushes the armature manually out of the coil the result is a burnt out coil.
    In the this case the inductive reactance changes drastically, but not so with DC, the coil resistance does not change.
    Max.
     
    Last edited: Sep 16, 2013
    R!f@@ likes this.
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    ?? I noticed you have answered a few questions regarding Inductance and DC?
    Max.
     
  17. #12

    Expert

    Nov 30, 2010
    16,246
    6,736
    Lovely chat, but it's beginning to look like a drive-by.
     
  18. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,786
    Yeah, but here we are talking about the effects of magnetic materials that are moving and how that affects the inductance and the transient. That's enough out of my realm of experience that I would have to pull out a book and spend some time with it at the very least. I would actually love to do exactly that, but I can't justify the time right now.
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,493
    2,363
    Regarding the O.P. it was mentioned that the solenoid required 1amp to actuate and 300ma to retain it.
    I believe he is talking about the phenomenon I mentioned where some method of lowering the voltage in order to take advantage of the lower current required in the retained state, not that these results would happen with a constant voltage.

    Seems he has left the building?
    Max.
     
  20. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,786
    I was thinking the same thing -- or that possibly he has AC solenoids and doesn't realize it?
     
Loading...