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24/12/5.5V selectable switch

  1. Jun 27, 2006 #1
    I am making a solenoid driver that are powering remote operated valves through a solid state relay circuit. I would like each port to have a selectable voltage level 24, 12, or 5.5V with a 3 state switch. I cannot find a 3 state switch that does the trick, however. They all are in a SPDT configuration (on-off-on). I need a switch that has a common path and then a way to select from 3 different inputs. What is the best way to do this?

    A switch that is PCB mountable is what I am needing. Thank you!
    -shad
     
  2. jcsd
  3. Jun 27, 2006 #2

    Danger

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    I might have an idea on this, but I need more information about the set-up. What do you mean by 'port'? Do all of the solenoids use the same voltage at the same time, or are they independently switchable? How many are there?
     
  4. Jun 27, 2006 #3
    Danger:

    I'm still nailing down the design plans. By port I really meant to say connection terminal for the solenoid. I want each solenoid to have a selectable voltage level. I will have a 24V power supply, a 12V DC-DC converter, and a 5V DC-DC converter. I am not sure if I can use a common ground between my power supply and the converters... my initial thought it yes, since it is the same power supply that is powering the converters. But to be honest, I haven't had much experience with the does and do nots of DC-DC converters.

    The switches will be mounted on the circuit board within the chassis. The switches will not be toggled once power is on, just to setup the ports. I could use a series of IDC pins and jumpers that would deliver what is expected at different configurations, but I am not the end user and would like it to be easy for the end users to switch the voltage coming out of any of the connection terminals.
     
  5. Jun 27, 2006 #4

    Danger

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    Okay, stand bye. I'll get working on it. By the way, there's no point in using multiple transformers. Just tap your power supply at various numbers of turns to pull off what you need.
     
  6. Jun 27, 2006 #5
    Just tap my power supply at various numbers of turns? Could you please explain more? Thanks!

    I'm not sure how many there will be. In the end, does it really matter? From the opto-isolated input from my controller each relay circuit is basically seperate minus the common ground.
     
  7. Jun 27, 2006 #6

    NoTime

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    Danger is thinking you are building your own power supply.
    For instance a 24v centertap transformer (easily found) can be used to construct a 24v and 12v power supply.
    If your solenoids will work with AC you could use this as is, without any additional circuitry.
    Finding a transformer with and additional 5v tap would be more of a challenge.

    For your original question, have you considered a rotory switch.
    These have a common input and mutiple outputs like you want.
     
  8. Jun 27, 2006 #7

    Danger

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    Here's what I had in mind. I have to do my cash-out and go home now; W's starving and wants to have supper right away. I'll come back in a bit and post the explanation of the circuit.

    [​IMG]

    edit: Okay, I'm back. As NoTime mentioned, centre-tap transformers are pretty common. I have one wall-wart that outputs 1.5, 3, 6, 9, or 12 dependent upon the switch setting. 5.5 might be hard to find in a hardware store unit. If you do decide to make your own supply, you just calculate how many turns of the secondary are needed to obtain a certain voltage and solder a take-off wire to that point (without cutting the coil). Tapping half-way along the windings of a 24V transformer will give you 12V, a quarter of the way will give you 6V, etc.. It's directly proportional.
    In my sketch, T1 is your 24V transformer with take-offs at the appropriate points. Sw1-3 are SP3T switches, all shown in the 'off' position. There's no way to accomplish your goal without using all three. I've drawn the set-up using barrier strips (bus bars), but printed circuit traces or soldered junctions would also work. S1-3 are the primary coils of the relays that drive your valves. Lastly, D1-3 are diodes to rectify the AC transformer output to DC. I was thinking that you could use LED's for that, so you'd have a visual indication of when each tap was in use. You might find it easier to put a single rectifier in the ground side (the little arrowheads are common grounds).
    I hope that this helps a bit, but please have someone with more electrical experience check it out before trying it.
     
    Last edited: Jun 27, 2006
  9. Jun 27, 2006 #8

    NoTime

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    Not bad Danger, but

    Since the idea seems to be to have the solenoid consume a specific amount of power.
    The half-wave rectification will half the time averaged power used by solenoid.
    The net effect is that the design as shown is a 2.5, 6 and 12 volt power supply.

    There are a number of ways to modify the basic layout that may or my not be sutible to the specific application.

    Another search key -> slide switch
     
  10. Jun 27, 2006 #9

    Danger

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    Crap! I didn't even think of that. It would be best then if he can obtain a wall-wart like mine and take the already-rectified current from the hot side of the switch. That 5.5 will be a nuissance, though. (Or, he could use a 48VDC transformer.)
    Thanks for pointing that out before it was too late.
     
  11. Jun 28, 2006 #10
    Thanks for the input guys. I think I failed to mention that these are DC voltages. Not only that, I would need a pretty large wall-wart to give me enough current. The solenoids draw about 500mA a peice (1.5mA if it is a 6V solenoid). I'm also planning to have around 12-16 connections, so it needs to be a high-end power supply, which I am not trained to build. To be honest, I didn't do well in my power classes and spent most of my time day dreaming about digital logic, control systems, communications, and antenna theory. That is why I'm willing to go with DC-DC converters since I know they will be more efficient then anything I jimmy rig.

    Danger: Those are the kind of switches I am looking for in your diagram! Where do you find these switches? I see...rotary switches are the kind I need. Hmm..ok, in my mind I saw a slide switch, but am having problems finding a 3-state slide switch in THAT configuration. I guess I'll look at rotary switches then.

    Thanks!
     
  12. Jun 28, 2006 #11

    Danger

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    Shadrack, I drew the switches as rotary because that's the easiest to draw with a minimum of wiring intersections (I had to do that in Paint because I was at work, and drawing those bridges was a pain in the ass). If you want high-capacity slide switches, I would recommend just grabbing some scrap 3-speed blow driers. That's what they use, and they can handle up to 1,500 watts.
     
  13. Jun 29, 2006 #12

    NoTime

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    Danger, you did that with paint?
    I'm impressed. :surprised
    You have way too much free time :smile:

    The average wall-wart (unless it is a switching type) will exhibit many of the same problems as your design.

    OP - If you don't have enough quantity to just go to a manufacturer, there are always places like Digikey and Newark.
     
  14. Jun 29, 2006 #13

    Danger

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    Thanks. Yeah, I have a nice job. :biggrin:
     
  15. Jul 28, 2006 #14

    Danger

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    So, Shadrack... it's been a month now. Just wondering how this came along for you.
     
  16. Jul 29, 2006 #15

    NoTime

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    He might still be in the furnace :biggrin:
     
  17. Jul 31, 2006 #16

    Danger

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    :rofl: ....
     
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