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Old 05-11-2012, 01:07 PM   #1
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Default Actuating valves using rotary switch + diodes?

Hey guys, I intend on having something more automated and computer-controlled in the future, but since I want to be able to brew something this year, I want to put together a cheap control panel. And since the valves I'm looking at don't have manual override, I need something that can actuate all the valves as needed.

So my idea was to put in a rotary switch carrying the PID's DC output, with each position keeping the right valves open or closed for each task - all closed/transfer strike water/recirculate the mash/sparge/recirculate boil through plate chiller to sanitize and whirlpool/chill and knock out/cleaning configuration... hopefully you get the point.

Only problem is that most if not all valves are going to be needed open for more than just a single task, and simply wiring it up would have the current travel back to the switch through the other wires connected to the valve and essentially energize all poles, resulting in all valves always being open.

Up until now, almost all my electrical work has been with AC power. But since the valves are powered by 12V DC, I'm thinking I can just wire the valves from the switch in parallel, and add a diode to each of these wires, as it's my understanding that diodes can be used to allow current to pass in only one direction, allowing current to go from the purposely energized pole on the switch while preventing it from traveling back to poles on the switch that I don't want energized.

Am I correct in assuming this will work? And if so, would somebody mind showing me the kind of diode I'll need to buy, and the correct way to orient it? As I really have no idea... the only diodes I've used in the past have been LEDs. And speaking of which... if I wanted, could I use LEDs to do the job to also get a visual representation on my panel of which valves are open? I'll be buying off Mouser, if someone would be so kind to show me the kind of diode I need, and hopefully explain the particular specs I need to look out for (and why).

And if the whole diode idea can't work, could someone explain why, and perhaps provide an alternative solution? I know I could achieve it using relays, but with the sheer number of valves multiplied by the numerous configurations I need, it would be hugely impractical, not to mention expensive - defeating the purpose of this whole thing.

Thanks in advance for any help that can be provided, and I'm crossing my fingers that I'm on to something with the switch + diodes idea, as it'd allow me to build a 50A control panel for dirt cheap while I save up for a much better monitoring + control solution.

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Old 05-11-2012, 05:26 PM   #2
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that sounds more complicated than its worth. i would just wire up a 3-way switch for each valve; center position would be off/normal state, up would be computer controlled, down would be manual control/on state. assuming all the valves have a common state (normally closed, lets say), then switching to manual mode would open the valve. turning the switch to center/off would close the valve.

are these solenoids or ball valves? what computer is going to be controlling them?

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Old 05-11-2012, 09:57 PM   #3
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Originally Posted by audger View Post
that sounds more complicated than its worth. i would just wire up a 3-way switch for each valve; center position would be off/normal state, up would be computer controlled, down would be manual control/on state. assuming all the valves have a common state (normally closed, lets say), then switching to manual mode would open the valve. turning the switch to center/off would close the valve.

are these solenoids or ball valves? what computer is going to be controlling them?
DO it!!
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Old 05-11-2012, 10:06 PM   #4
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I'm not sure what you're proposing with the rotary switch, but all you need is a diode that can carry the current. I'd use a Schottky diode which will have a much lower forward voltage drop (and will use less power). Diodes have a line on one end of them that marks the cathode... the downstream side. That's about it. Diodes are pretty easy! You should also make sure the reverse voltage limit of the diode is rated for whatever voltage you're using, but I doubt that would be a problem here. Radio shack probably has some crappy diodes that would work fine for you.

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Old 05-11-2012, 10:48 PM   #5
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I have a couple of 120 vac to 24 vac rectifires if you need them pst me I will be more than fair with the price.

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Old 05-11-2012, 11:22 PM   #6
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Quote:
Originally Posted by audger
that sounds more complicated than its worth. i would just wire up a 3-way switch for each valve; center position would be off/normal state, up would be computer controlled, down would be manual control/on state. assuming all the valves have a common state (normally closed, lets say), then switching to manual mode would open the valve. turning the switch to center/off would close the valve.

are these solenoids or ball valves? what computer is going to be controlling them?
Ball Valves. This control panel has nothing to do with the computer control I'll add later. The reason I want to put it all on a rotary switch is because there are a LOT of valves, and controlling them one by one gets complicated - otherwise I wouldn't even bother with motorized valves.
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Old 05-12-2012, 12:02 AM   #7
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Quote:
Originally Posted by passedpawn
I'm not sure what you're proposing with the rotary switch, but all you need is a diode that can carry the current. I'd use a Schottky diode which will have a much lower forward voltage drop (and will use less power). Diodes have a line on one end of them that marks the cathode... the downstream side. That's about it. Diodes are pretty easy! You should also make sure the reverse voltage limit of the diode is rated for whatever voltage you're using, but I doubt that would be a problem here. Radio shack probably has some crappy diodes that would work fine for you.
The rotary switch is to provide a level of automation. For example:

Position 1: All valves closed
Position 2: Only open valves for transferring strike water
Position 3: Only open valves needed to recirculate mash
etc...

The reason I think I need diodes is because, for example, if the switch is in position 2 and it opens a valve that is also opened by positions 3 and 6, the current will travel back to pole 3 and 6 (since the valve is also wired to them) and energize them as well, eventually opening up all sorts of valves I want closed. My thought is that simply placing a diode in between the switch and every valve will allow me to prevent this.

Is this correct, or no?
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Old 05-12-2012, 04:11 AM   #8
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Okay, instead of using a rotary switch I'm going to use simple rocker switches, one for each combination of open/closed valves I'll need to use. For example, turning on the mash recirc switch will open up only the valves needed to recirculate the mash.

Since some valves are going to be opened by more than one switch, I'll still need diodes to prevent current from energizing any switch that's connected to an open valve (which would open other valves that I want closed). Can somebody just confirm that the diodes will accomplish what I want? And perhaps show me on www.mouser.com the specific diode I should order (the valves operate on 12VDC)?

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Old 05-12-2012, 04:48 PM   #9
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Yes diodes will accomplish what you want

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Old 05-13-2012, 01:03 AM   #10
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Quote:
Originally Posted by crane
Yes diodes will accomplish what you want
Thank you. Now I just need to figure out what type of diode is most appropriate, and whatever the particular specs I need.

Does running current backwards across an LED ruin it? I may just use LEDs if I can maintain enough voltage to the valves, and give myself a nice little indicator diagram.
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