rotary switch AC DC ratings

Discussion in 'General Electronics Chat' started by seesoe, Dec 21, 2011.

  1. seesoe

    Thread Starter Active Member

    Dec 7, 2008
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    0
    hello,

    i have a manifold of 3 solenoids, 0.17 Amp at 120 Vac each, would i be able to control them with the following rotary switch?
    ROTP3P4 - rated at 0.3 Amp at 30 Vdc

    this is for a large scale product, and just wanted to be confident that the contacts don't burn prematurely/rapidly.

    sorry for the noob question!
    thanks
    seesoe
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    120 VAC RMS is 170 V Peak ,so I will suggest not to do it and I think in AAC high voltage thread like this one may not be allowed.

    Good Luck
     
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    both the amp and the volt rating on switches is important and should not be taken shortcuts in this area. The higher the voltage, the more likely to arc. on a rotary switch like that, imagine if electricity were to arc over to another contact; unintended operations could occur, especially while you are moving the dial, and the contact is between positions. if this switch is controlling solenoids, which control cylinders, which people are working with, I can see someone getting crushed by a runaway cylinder. and yes, if the contacts burning up are your only worries, they will.
     
  4. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Wafer switches open far too slowly to be able to extinguish the arc--the inductive load and high voltage further exacerbate the problem.

    Check out this switch that is available on ebay.
     
    strantor likes this.
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    good recommendation. that's a good brand, and a good price. a much more robust design than the one OP linked to.
     
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    If you want to use that switch, you will have to use it as a low voltage, low current controller for something like this:
    http://search.digikey.com/scripts/D...ng=en&site=us&keywords=PR39MF51NSZF&x=15&y=18
    That is a solid state relay, aka SSR. It works more or less like an optocoupler, except it's for AC. That one is rated for 0.9A @ 240V.

    The advantage of using an SSR like that is it will turn off during the AC's zero crossing, which will avoid an inductive spike in the solenoid circuit. Also, the current through the rotary switch only needs to be ~20mA at a few volts; a fraction of its' rating.
     
  7. seesoe

    Thread Starter Active Member

    Dec 7, 2008
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    thank you for the reply's. the product needs 6 switches and 18 solenoids. using a $15 switch is out of the question. the solenoids valves aren't opening anything important, just atmospheric pressure air.

    what about something like the RBS-3-4?

    the manufacture offers the solenoid valve coils in 3 voltages,
    1.4 A at 12VDC.
    0.75 A at 24VDC
    0.17A at 110VAC

    i was using the 12vdc coils, however, 1.4 amps is very high and it was producing an immense amount of heat, so i was hoping to reduce this heat for safety reasons by using the 120vac coils

    unfortunately, i think im going to end up taking the route SgtWookie suggested, by using a secondary relay system.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    12v @ 1.4A is 16.8 Watts; 110VAC @ 0.17A is 18.7 Watts - so that solenoid would actually dissipate MORE power than the 12v solenoid.

    There are solenoid drivers you can get in IC form; they provide full power to the solenoid when it's engaging; after a short period of time the current flow is reduced via PWM. This helps a great deal in reducing the power consumption of the solenoid. It usually takes far more power for the initial actuation than it does to hold the solenoid in place. [eta] Whoops, I was thinking of the DRV101; just priced them out and they've gone up considerably since I last looked; around $6/ea.

    That rotary switch would work with the 0.17A @ 110V, but the website states that the switch is "light duty". That means it'll fall apart if you look at it cross-eyed.

    That switch is different from the previous one in that the previous was a make-before-break, where this one is a break-before-make. What that means is the previous switch would have two outputs on at once when moving between switch positions. This new one would not have more than 1 output on at any time.
     
  9. seesoe

    Thread Starter Active Member

    Dec 7, 2008
    99
    0
    hmm, interesting, since the coils dissipate about the same amount of power, would you recommend i use the 12v coil over the 120v coil?
    if so would the first switch work fine? or would it still be best to have some sort of ssr or driver inline?
    thanks
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Neither switch is rated for the current that the 12VDC solenoids require. However, you could use the rotary switch to turn on N-ch MOSFETs - but even there you'll be running about a buck per MOSFET.

    No, the 1st switch is not suitable for any of the solenoids to drive directly. It could work with a MOSFET or TRIAC. However, it looks just like this "light duty" switch, so don't expect them to last long.

    If you are going to use an electromechanical switch, particularly cheap ones, you would be better off using drivers for your solenoids.

    Now if you want to make your product more reliable, while still keeping the costs down, you would use something like tactile pushbuttons, a microcontroller, and either TRIACs for AC or MOSFETs for DC control of the solenoids.

    You could program a microcontroller to give a solenoid full power during turn-on, and then leave it in a PWM mode to keep it engaged at a lower power. This will make your product more energy efficient, and also leaves the possibility of selling customers on options for program features and upgrades.
     
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