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"Input" on an "output"

Started by Don Y September 15, 2013
Hi Charlie,

On 9/16/2013 12:19 PM, Charlie E. wrote:

> The joys of plumbing!
You've been inhaling too many solder fumes, Charlie. As I recall it, it's _The Joy of *SEX*_! :>
> My hose bib in the back yard started leaking. Got a new washer, > turned off the water, and tried taking it apart. An hour later, I > gave up! Can't get the stem out, looks like lime build up is so thick > that it has made its own washer in there. So, it looks like it is > time to replace the hose bib. > > Go into Home Depot, talk to gal there, and she gives me something > called a sharkbite fitting. You just cut off the old sweated on hose > bib and put it on and screw on a new hose bib. Sounds doable. > > Next day, turn off water and go to get to work. First, I compare the > new fittings and the existing - not the same size! She gave me a 1/2" > sharkbite, but OD of existing is 1". Turn water back on... > > Go back to Home Depot, looking for pipe with OD of 1". She doesn't > know of anything like that. Brings in old guy (my age!) and he thinks > about it, and figures it out. Plumber used 3/4" pipe and a 1/2" hose > bib, but sweated a coupler across both. Coupler would be flush with > stucco wall. So, now I have a torch and plumbing kit, a new 3/4" > sweat to male thread, and a new 3/4" hose bib. > > So, now I have a new adventure - learning to sweat pipe! Any hints > and suggestions? Pipe is painted white - do I need to remove paint > first, or just burn it off with torch? How hard is it to sweat off a > coupler like this? Any advice will be appreciated!
There are lots of tutorials on-line that will help you with the details of sweatig a joint (with photos, etc.). So, I'll only concentrate on the stuff they tend to forget to tell you! First things first. Some general things to know... "Plumbing takes THREE trips". By my count, you've only made *two*! So, plan on (at least) one more! :-/ Don't use a ball valve for a hose bibb or any other "rate control" valve. A ball valve can only be used as a "stop" (full on/full off). Operating it in any other position will lead to erosion (aka valve failure) -- esp with aggressive water! They are also problematic in that they can be operated "too quickly" (think: "water hammer") which can actually cause bits of plumbing and appliances to *fail* [I suspect you have NOT purchased a ball valve so this shouldn't apply to you] Consider using a "boiler drain" instead of a hose bibb. Most hose bibbs have the operating handle/knob oriented parallel to the ground *or* at a 45 degree incline therefrom. As the knob ends up very close to the wall of the house, operating the knob with your hand ends up scraping your knuckles against the side of the house. Not a big deal if your house is clad in cedar shingles. But, a different experience, entirely, when your knuckles are brushing up against stucco! As a rule of thumb, the diameter of the pipe determines how far the pipe is intended to penetrate into fittings. E.g., a 3/4" pipe will extend 3/4" into any fitting to which it is intended to mate. You can skim A LITTLE if need be (e.g., 5/8" if your pipe is 1/8" too short) but Code wants this nominal penetration (and I tend to think the folks who write the Code know more about this stuff than I *ever* will -- so I just trust them!) Give yourself room to work. Trying to sweat a joint through a tiny hole in the wall is just not worth the effort! Make the hole bigger and plan on fixing it later. This will also improve your visibility so you can check your work afterwards. Have a pliers (I prefer needle nose for the sort of thing you are doing as they don't have as much of "heat sink" effect as, for example, gas pliers), wet rag (an old wash cloth is ideal) and flux brush on hand (along with solder, of course). Wrap jaws of pliers with masking/duct tape to prevent them from marring "finished" surfaces -- esp for softer metals like the castings used for the hose bibbs, etc. I just use the "wet rag" that I have on hand -- wrap it around the fixture I am trying to tighten, then let jaws of pliers or pipe wrench bite into *that* instead of the metal beneath. Remove all paint first. Ideally, with solvent taking care not to get stuff *into* the pipe as that's potable water elsewhere in your house! (also, avoid having open flame around when using any solvent -- most like to burn brightly!). If solvent won't do the trick, emery cloth or steel wool can be used. Just remember that copper is really soft and it is easy to remove lots of metal without realizing it! (you want to try to maintain the nominal O.D. of the pipe for a good fit with the fitting you'll be attaching). The sweet spot is located at the tip of the inner blue flame from the torch. Don't be stingy with the propane (make sure you have a reasonably sized flame) yet don't be wasteful, either! Too large a flame can blow itself out! Heat the *fitting*, not the pipe! Fitting will expand making it easier to remove from the pipe. When soldering, this action will serve to draw solder into the gap between the pipe and the fitting. Apply solder to the gap between pipe and fitting. You may find it helpful to bend the last few inches of the ROLLED solder into a 'J' shape so you can apply it to the "back side" of this fitting (as you will be "outside" looking in). Solder is a handy tool for telling if the *old* solder has liquified, yet (when removing old fitting). Don't use pliers until the instant before you want to remove fitting as they will draw LOTS of heat away from the part and cause heated solder to resolidify. Things cool off quickly so have everything ready before you get started. E.g., don't start heating the fitting and *then* go looking for a pair of pliers. Of course, "cool off" is entirely relative. You'll find that things cool down to the point where the solder resolidifies very quickly! But, seem to take an eternity to cool to the point where they are safe to touch! :< When removing an existing fitting, you have to pull "straight" off as if you get it cocked it will bind and probably cool off enough to reattach itself in this new orientation (cuz you probably can't keep the torch on the fixture *while* you are pulling it off). As soon as the pliers touch the work, it will begin to RAPIDLY cool! [You want to avoid putting too much heat into that area because you risk heating the pipe *behind* it and having THAT come off in the process. Then you have a bigger task: replacing a fitting that's even further inside the wall!] When fitting has been removed, you can EASILY reheat the end of the pipe to reliquify any remaining solder. This can be brushed off with the flux brush. Or, wiped off with the wet rag (but you need to use a very fast motion as the rag cools the pipe very quickly causing the solder to resolidify). Emery cloth and/or steel wool will knock down any fine high spots to allow the new fitting to slide on. At least once -- probably several times! -- during this sort of operation, you will be *sorely* tempted to reach out with your hand and grab the work. Resist this temptation. You will yield to it AT MOST *once*. Thereafter, the sound of melting flesh will be indelibly etched into your memory -- along with the pain that accompanies it a few ohnoseconds later! Oh, and did I mention DON'T TOUCH THE HEATED PART(s)? Or, put them anywhere that won't appreciate their latent heat?? (e.g., don't have your pets snooping around behind you while you're working) ---- As for your specific situation... I'd reconsider the choice of "male adapter" in favor of a *female* adapter and a male hose bibb (or, boiler drain, as I suggested) to mate with it. When your house was originally plumbed, the plumber could easily access the pipe & fitting from EACH side of the wall! So, he could position the bibb on the pipe *exactly* where he wanted it (i.e., so the hose bibb was flush against the exterior of the house -- even if the exterior wasn't in place, yet!). Then, sweat the joint and move on... In your case, you are planning to sweat the male adapter onto the pipe (once you've removed the coupler that is there, currently). Then, you are going to screw the (female) bibb onto this. But, you there is *one* spot where the bibb will be mated adequately to the male adapter. You'll have to ensure the male garden hose (MGH) connection is pointed *down*. And, that the bibb is screwed on "enough" that the join between bibb and adapter won't leak (leaks INSIDE walls are big problems). So, here's the problem: you are going to solder that male adapter onto the pipe. This will place the end of the adapter at some point in space relative to the outer surface of your house. If too far out, then you won't be able to snug the hose bibb up against the house "tight" (bibb probably wants to be fastened to the house mechanically). If not far enough out, then the bibb will bottom out against the wall of your house before the threaded connection is tight enough. You can try to do a dry run of this by threading the bibb onto the fitting *before* sweating the fitting onto the pipe. Then, slide this assembly onto the cleaned end of the pipe to see where things settle out. If all is well, you can note the orientation of the male adapter (i.e., if you rotate it 180 degrees, then the bibb won't fit the same!) wrt "top" and remove it from the bibb prior to sweating it onto the pipe. If you have to cut the pipe to get the assembly to fit flush against the house, then you'll probably need a "tight fit" pipe cutter. These are very small -- not the traditional style that requires several inches of clearance to "swing around" the pipe. But, they are a real PITA to use -- esp on larger dia pipes! If you have to extend the pipe to get the assembly to fully engage the pipe, then you'll have to lengthen the pipe. Or, hunt around for a different fixture that might let you kludge a solution! [If you have to extend the pipe, make sure you debur the ends of any new pieces that you *cut* prior to adding them. Otherwise you can end up with an annoying "whistle" and, potentially, "pinholing" of the pipe itself as the turbulence eats away at it. Type L pipe is always preferable to type M -- heavier.] When faced with this decision, here, I opted to terminate each pipe with a *female* adapter. Both male and female adapters look like large hex nuts. This allows you to put a backing wrench on the adapter to keep *it* from rotating (or being torqued!) as you screw the mating device onto/into it -- with another wrench! For a hose bibb with a "skirt" that hides the hole in the wall, you can't access this "nut" while you are screwing the hose bibb onto the (male) adapter. This puts strain on the pipe and adapter (big deal! just don't go all King Kong and you shouldn't have a problem) With a *female* adapter, I could "set" the adapter into the wall such that *just* the "nut" portion protruded from the wall. Then, use a *male* hose bibb that I could screw into this adapter WHILE HOLDING THE ADAPTER IN PLACE WITH A BACKING WRENCH. [As I said, I used boiler drains -- which are inherently "male" (think "hot water heater drain valve") -- so the knobs ended up parallel to the house instead of inclined into it (or normal to it!)] No idea what sort of mechanical issues you will face. A "hose connection" (bibb, boiler drain, etc.) sees a fair bit of mechanical stress so you want to be sure the pipe and "faucet" are supported well. In my case, this is set in concrete so it's not going anywhere. If you are dealing with stucco over wood framing, you may want to look at the more conventional bibbs as they have a means of mounting the "skirt" to the structure of the house. As with most projects, if you get tired/frustrated, stop and tackle it later when you've a clearer head. You don't want to burn the house down because you were sloppy! Or, melt some wires in the wall, etc. Most important piece of information: plan on doing this early in the day (but AFTER your main water needs have been satisfied) so you can make one (or three) trips to the store before darkness sets in! (or the stores close) I'll try to find a photo of what I did to give you an idea. And, of course, you can always *ask* for clarification! :> (I use lots of words in the hope of being clear -- yet seem to always take something for granted that leaves others confused :< ) --don
On 9/16/2013 2:04 PM, rickman wrote:
> On 9/16/2013 12:39 AM, Don Y wrote:
>>>> The manual valve ("faucet") is DOWNstream from the electric valve. >>>> It is used to set the *rate* of flow. Including "off", if need be. >>>> >>>> Do *you* always use a garden hose with the "faucet" wide open? >>>> Or, do you use the "faucet" to adjust the flow to a rate that is >>>> appropriate for *how* you are *using* the water?
>> No. You're assuming that one valve also does metering. That >> changes the requirements ($$) for the valve -- > > I don't get why you have the electric valves. What are they for when > your mechanical valve is right there?
All of the plantings in the yard have "drip" irrigation available at each rootball. The size of the rootball varies with the age of the planting. E.g., a freshly plated tree might have a rootball 12" dia. A *mature* tree wants to be watered farther out from the trunk (watering at the trunk is a bad idea as it weakens the tree's support in the ground and the water isn't taken up into the plant, effectively). E.g., a tree with a 20 ft crown wants to be watered ~6-8 ft away from the trunk. So, you make a new planting and now have to ensure it gets watered. Where do you locate the "emitters"? A few inches from the "trunk" so the water will seep into the gound where it can be accessed by the roots in that 12" dia rootball? Or, several *feet* away in anticipation of where the roots will *ultimately* be located? If you choose the former, then you will have to move the emitters farther out as the plant matures. If you choose the latter, the plant will die from dehydration before it's roots ever reach the locations of the emitters! [I am not keen about doing the same thing twice, needlessly. Esp if that thing involves digging in the yard! :> ] My solution is to have "adjustable" emitters -- in the form of garden hoses that can be placed *exactly* where a new planting can get at it's water supply. And, a "flow control" (manual valve) that ensures the water doesn't drown the plant each time the faucet is opened! In use: run the end of a garden hose to a spot near the base of a new planting; manually adjust the flow rate to something that "looks about right"; tell the irrigation controller to actuate the valve associated with that garden hose for X minutes every day (for the first weeks) then Y minutes every *other* day (for the next week) then Z minutes... And, each week, move the hose a bit farther away from the "trunk" as the root systems grow outward. Once the root systems are established enough that the "final" emitter placement can satisfy their needs, roll the hose up and cancel the "program" for that "zone" on the controller. E.g., we lost three citrus trees last year (or the year before... I forget). The citrus trees are fed water at a high flow rate (because they *use* a lot of water!). You don't want "standing water" against the trunk of a citrus tree because it leads to gumiosis (sp?). So, the "emitters" ("shrubblers", in this case) are located a few feet away from the trunk. They fill a "mote" that surrounds each tree. This is filled to a depth of about 3", allowed to seep into the soil, refilled, allowed to seep, and refilled (again). This ensures adequate water for good fruit development as well as helping to flush the salts present in the water and soil down *below* the roots. The *four* (i.e., one of which has no "previous location" that it can occupy) new plantings are tiny: "1 gallon" pots (about 6" dia). So, the root systems haven't a chance in hell of ever reaching that "mote" located several feet away from the trunk! Solution: run garden hose to each new planting and let the hose provide the water needs until the plant is "established". Similarly, if you discover a plant is NOT getting watered enough, you can hack together a kludge to provide supplemental water to *just* that plant -- without providing EXTRA water to all of the other plants fed by that irrigation "zone". Then, when you have the time to do so, you can replace the emitters on that particular plant with something having a larger flow rate (which gives *that* plant more water per unit time without affecting the water supplied to the other plants on that zone)
> About your proposed approach with a current limited driver for the > solenoids and a button to activate the current limit, I don't get the > problem. The solenoid will draw some current, but it will be for a > considerable time. The button will draw a current for a short time. The > discriminator will be time, not current.
The current limiter is to prevent a shorted coil from pulling down the power supply and crippling the other valves in the system. I.e., solenoid should draw 0.3A inrush, 0.2A holding. If it ever draws 0.5A then something is broken! If it tries to draw many *amps*, something is SHORTED! You don't want to have to replace a drive transistor because it tried to pass the full output current available through a short. Nor do you want to add fuses. Instead, let the supply go into limit. That protects the output driver as well as ensuring that one driver doesn't render the entire output system unusable (because you may want to operate several valves concurrently and don't want valve 1 to pull down Vcc to a point where valve 13 won't actuate!)
> The PSU will not need to limit the current as much as measure it. The
It has to do both -- but, how finely it measures is debatable. All it has to do is be able to differentiate among different types of load conditions (shorted coil, opened coil, button pressed, button pressed while coil energized, coil shorted to ANOTHER coil, etc.)
> button can have a simple resistor to set the button current draw. If a > current change is seen that lasts for the right amount of time it is > considered a button push. Currents for other time profiles will be > considered the solenoid or a fault. It would even be possible to > implement other commands with other time durations. 0.5 second press > turns on/off this faucet, 3 second press turns off *all* faucets for > example. > > What ever you are using for a controller would need to be programmable > at an appropriate level to implement this.
That's the easy part. Tough part is getting the information I need across the isolation barrier without using anything precious or "fragile" on the field side of that barrier (cuz you have to expect a very hostile environment, there).
Hi Spehro,

On 9/16/2013 12:51 PM, Spehro Pefhany wrote:
> On Mon, 16 Sep 2013 12:19:21 -0700, Charlie E. <edmondson@ieee.org> > wrote: > >> So, now I have a new adventure - learning to sweat pipe! Any hints >> and suggestions? Pipe is painted white - do I need to remove paint >> first, or just burn it off with torch? How hard is it to sweat off a >> coupler like this? Any advice will be appreciated! > > Don't burn the house down would be my advice. > > Soldering copper pipe is really easy if the parts are fluxed and > bright-clean or already tinned. It's about impossible if they're dirty > or there is a slow drip of water. > > The trick I learned to deal with the latter is to stuff a plug of > white bread (no crust) into the pipe. The bread dissolves later.
Hmmm... never heard that one! I've always used a lightweight rag and never added more than one fitting at a time before fishing it *through* the newly attached fitting. I'll keep this approach in mind as I have to install a pressure reducing valve on the supply, here. And, of course, the gate valve that the city installs at the meter ain't worth squat 30+ years later (i.e., so it won't close off the flow to the house completely while I am working). Not real anxious to get started on this as any screwup leaves us without water until its resolved! :<
On 9/15/2013 3:31 PM, Don Y wrote:
> Hi, > > I've added four hose bibbs around the yard, each behind an > electric solenoid (24V). The intent is for supplemental irrigation > for new plantings, etc. (attach hose to hose bibb; run hose > out to be proximate to the new planting; "program" irrigation > system to dispense water via this particular "hose circuit" > for the several weeks required to get root system established) > > I'd like to be able to *manually* signal the irrigation > system that I would like the electric valve engaged (and, > later, possibly disengaged!). But, I don't really have a > spare conductor to dedicate to that purpose. :< > > So, I figure I could *share* the "solenoid drive" function with > the "button sense" function. > > (remember, this is outdoors in the weather so I'm not keen on > putting any electronics out there that won't appreciate the > heat, cold, water, sun, etc.) > > I figure I can wire a NO button across the valve solenoid (either > directly or with some series resistance). Then, on the driving > side, sense this "short" when the solenoid is NOT energized (i.e., > please turn ON the valve) as well as when it *is* energized (i.e., > please turn OFF the valve). > > [Similarly, I could add a NC button in series and "probe" the > load when off vs. on] > > Any suggestions as to other issues that would make one of these > approaches better/worse than the other? Off hand, the NC in > series seems like it would be more troublesome (i.e., if the > button failed, the valve is not usable). > > Or, cleverer solutions? > > (I'll have to characterize the valves - and hope any replacements > in the future are similar!) > > Thx, > --don
Here's a conceptual description of how you could do it that will meet your requirement that there be no electronics (other than the switch) at the solenoid locations. You'll need to provide power to the solenoid at all times for the switch idea to work. For that, you'll need a low voltage power supply in addition to your existing power supply to the solenoid. (You could derive the low voltage from the existing supply if you want.) The low voltage supply will allow you to sense the status of the switch without forcing enough current through the solenoid to energize it or to cause a lot of heat in it. N/O -------- +-----o o-------+ | New | | | | Power |---+---[Solenoid]---+ | Supply | | | Low V |-----+---[R]---+----+ -------- | | |<---V--->| R is high wattage low resistance, chosen to allow reliable operation of the solenoid with your existing supply. V is the voltage developed across R, which will be higher when the push button switch is pressed than when the solenoid is not shorted by the switch. You'll get 4 different voltages across R: V1 - voltage with low V supply connected, switch not pressed V2 - voltage with low V supply connected, switch pressed V3 - voltage with high V supply connected, switch not pressed V4 - voltage with high V supply connected, switch pressed V2 and V4 can initiate turning the solenoid on or off: V2 detected - turn solenoid on 1) disconnect low v 2) connect high v V4 detected - turn solenoid off 1) disconnect high v 2) connect low v You'll also need a delay to prevent false switching during transitions or if the switch is pressed too long. All the electronics can be installed at your existing controller location, with the switches installed at the solenoid locations. Ed
On 9/16/2013 9:03 PM, Don Y wrote:
> > That's the easy part. Tough part is getting the information I need > across the isolation barrier without using anything precious or > "fragile" on the field side of that barrier (cuz you have to expect > a very hostile environment, there).
You used some thousand words describing your plants and how you want to water them and I don't think you have really explained the problem well. I don't need to know the details of how you water your plants, I just need to know the relevant details. Of course all power supplies should limit the output power to the load to prevent catastrophic failures. My point is you don't need to draw this full current when you press the switch. If you did that, you would be drawing the PSU down and all other solenoids on the same PSU would deactivate. Another issue in using the switch with the full current limit of the PSU depends on the current and the rating of the switch, but it may well run excessive current though the switch. BTW, coils are not specified for "inrush" and "holding". They are specified for pull in and drop out. These are typically voltages and specify the level at which the solenoid is guaranteed to pull in or drop out. Coils don't have "inrush" current, that would be a capacitor. Coils resist changes in current, so when you apply a voltage the current goes up gradually (even if gradually is quick). It doesn't spike up and then drop back. I don't recall you mentioning an "isolation" barrier before. Where in the system is that currently? Is that in your controller? Where do you expect to add your electronics? How will the power to the solenoid be controlled by the switch? I don't mean the switch sensing, I mean the control. Once you sense the switch, how does the solenoid get controlled? You haven't told me enough information to help you. BTW, this is *not* a difficult design task. I don't think there will be a "tough" part once I understand fully the issues involved. -- Rick
Hi Ed,

On 9/16/2013 10:17 PM, ehsjr wrote:
> On 9/15/2013 3:31 PM, Don Y wrote:
>> So, I figure I could *share* the "solenoid drive" function with >> the "button sense" function. >> >> (remember, this is outdoors in the weather so I'm not keen on >> putting any electronics out there that won't appreciate the >> heat, cold, water, sun, etc.) >> >> I figure I can wire a NO button across the valve solenoid (either >> directly or with some series resistance). Then, on the driving >> side, sense this "short" when the solenoid is NOT energized (i.e., >> please turn ON the valve) as well as when it *is* energized (i.e., >> please turn OFF the valve).
> Here's a conceptual description of how you could do it that > will meet your requirement that there be no electronics (other > than the switch) at the solenoid locations.
Nice goal!
> You'll need to provide power to the solenoid at all times for > the switch idea to work.
Actually, if the solenoid is "off", I can "poll" the circuit instead of leaving power on all the time...
> For that, you'll need a low voltage > power supply in addition to your existing power supply to the > solenoid. (You could derive the low voltage from the existing > supply if you want.) The low voltage supply will allow you to > sense the status of the switch without forcing enough current > through the solenoid to energize it or to cause a lot of heat > in it. > > N/O > -------- +-----o o-------+ > | New | | | > | Power |---+---[Solenoid]---+ > | Supply | | > | Low V |-----+---[R]---+----+ > -------- | | > |<---V--->| > > R is high wattage low resistance, chosen to allow reliable > operation of the solenoid with your existing supply. V
You are sensing V *behind* the solenoid's resistance -- O(120 ohms).
> is the voltage developed across R, which will be higher when > the push button switch is pressed than when the solenoid is > not shorted by the switch.
If the switch fails shorted, then the solenoid doesn't work. This is the same sort of problem Spehro's NC approach has -- the circuit needs immediate attention (because the solenoid can't perform its normal function -- even though ONLY the button is broken) Also, the solenoid effectively "turns off" when the button is pressed. So, if the controller does NOT want to turn it off, it ends up "pulsing" off (while the switch is pressed) and then back on (after the switch is released and the controller has decided to "leave it on"). I.e., this approach has the switch dominating the "control" output.
> You'll get 4 different voltages across R: > V1 - voltage with low V supply connected, switch not pressed > V2 - voltage with low V supply connected, switch pressed > V3 - voltage with high V supply connected, switch not pressed > V4 - voltage with high V supply connected, switch pressed > > V2 and V4 can initiate turning the solenoid on or off: > V2 detected - turn solenoid on > 1) disconnect low v 2) connect high v > V4 detected - turn solenoid off > 1) disconnect high v 2) connect low v > > You'll also need a delay to prevent false switching during > transitions or if the switch is pressed too long. > > All the electronics can be installed at your existing controller > location, with the switches installed at the solenoid locations.
I'm currently looking at a design wherein the resistor is colocated with the switch. Then, monitoring the current drawn in each "circuit" to characterize the instantaneous load seen by that circuit. The trick is to see how coarsely I can quantify the current while still garnering as much information about the load and what it likely represents. E.g., shorted coil, open coil, two coils driven by a single output (unintentionally), missing Vcc at one or more coils, etc. And, throw the button into this mix as yet another variable... Wanting all of this to be isolated and "robust" makes it a bit more challenging -- can't just hang an A/DC out there and read the sense current. But, I think it essential that: - the drivers not be prone to failure in conditions that you *expect* to encounter in a deployed scenario (miswired, shorted, opened, etc.) - you alert the user to as many problems as possible that could be impacting the actual delivery of water to the irrigation zones (cuz there are other zones that may not have buttons; ideally, treat them all the same!) - the design not rely on characteristics of some specific solenoid Ideally, I'd add a flow rate sensor to the irrigation supply line but that's not high on the priority list... I am hoping to ultimately be able to watch the city water meter and compare its readings with those from my "potable water reading" to deduce what must be flowing outside the house (e.g., there is one hose bibb that I have no control over)
On 9/16/2013 11:28 PM, rickman wrote:
> On 9/16/2013 9:03 PM, Don Y wrote: >> >> That's the easy part. Tough part is getting the information I need >> across the isolation barrier without using anything precious or >> "fragile" on the field side of that barrier (cuz you have to expect >> a very hostile environment, there). > > You used some thousand words describing your plants and how you want to > water them and I don't think you have really explained the problem well. > I don't need to know the details of how you water your plants, I just > need to know the relevant details.
You wanted to know why I needed an electric valve. Would you have been happy had I replied, "Because."? I find understanding an *application* ends up saving questions later. "Why do you need to do that?"
> Of course all power supplies should limit the output power to the load > to prevent catastrophic failures. My point is you don't need to draw > this full current when you press the switch. If you did that, you would > be drawing the PSU down and all other solenoids on the same PSU would > deactivate. Another issue in using the switch with the full current > limit of the PSU depends on the current and the rating of the switch, > but it may well run excessive current though the switch.
I didn't claim that the switch would cause the supply to hit its current limit. Rather, that the supply *was* current limited as part of any reasonable such application.
> BTW, coils are not specified for "inrush" and "holding". They are > specified for pull in and drop out. These are typically voltages and > specify the level at which the solenoid is guaranteed to pull in or drop > out. Coils don't have "inrush" current, that would be a capacitor. > Coils resist changes in current, so when you apply a voltage the current > goes up gradually (even if gradually is quick). It doesn't spike up and > then drop back.
Excuse me, but the solenoids (coils) used in irrigation systems *are* rated as "inrush" and "holding" current. That's what you will find on their "datasheets" when you go hunting for specifics. You can always be pedantic -- and your end user will end up calling the solenoid vendor: "Hi, could you please tell me what the pull-in voltage is for the solenoid used on your model ABC irrigation valve? And, while you're at it, could you please tell me what the drop-out voltage is? What's that -- yes, these are running off a 24V system as indicated on the box that they came in... So, why do I need these numbers, you ask...?" Speak the language appropriate for the application domain you're working in. :>
> I don't recall you mentioning an "isolation" barrier before. Where in > the system is that currently? Is that in your controller? Where do you > expect to add your electronics? How will the power to the solenoid be > controlled by the switch? I don't mean the switch sensing, I mean the > control. Once you sense the switch, how does the solenoid get controlled?
Currently, the controller just drives the 15 irrigation valves with a darlington and flyback. No isolation at all -- the controller is just an SBC from a design I did for a client many years ago that I had repurposed for this role, temporarily. *New* design will be expressly for irrigation controller. As such, outputs will need to be isolated from the "logic", communication network, power for those electronics, etc. You can expect to encounter large voltage spikes (lightning strikes) as well as deliberate attempts to subvert the electronics "inside" that isolation barrier. The user will see a network connection to the controller (which powers the "smarts"), a connection for "valve power", and wires running off to the individual solenoids (15+master -- though that would probably increase as the electronics for an individual valves represent a small cost). Additionally, connections to a flow meter and water treatment appliances (basically, just more isolated DIO's). The button is just a button. I *choose* to use it to signal actions for that particular electric valve. I could just as easily use it to open the garage door... it just happens to use the same "conductor" as the solenoid valve. (e.g., I will eventually use this to control portions of the laundry, the hot water heater and the garage door opener -- as these are all just "isolated DIO applications")
> You haven't told me enough information to help you. > > BTW, this is *not* a difficult design task. I don't think there will be > a "tough" part once I understand fully the issues involved.
I think I've already got a flexible solution that should give me everything I need. I just have to consider each likely failure (in the field wiring) to verify that I can detect each such condition. I.e., so I can report problems before they affect actual operations. (you'd like to know a valve wasn't operational/controllable BEFORE the plants serviced by it dried up and died; you'd also like to know that your connection to the garage door opener was ineffective before you tried to open it!) Thx! --don
On 9/17/2013 3:07 AM, Don Y wrote:
> On 9/16/2013 11:28 PM, rickman wrote: >> On 9/16/2013 9:03 PM, Don Y wrote: >>> >>> That's the easy part. Tough part is getting the information I need >>> across the isolation barrier without using anything precious or >>> "fragile" on the field side of that barrier (cuz you have to expect >>> a very hostile environment, there). >> >> You used some thousand words describing your plants and how you want to >> water them and I don't think you have really explained the problem well. >> I don't need to know the details of how you water your plants, I just >> need to know the relevant details. > > You wanted to know why I needed an electric valve. Would > you have been happy had I replied, "Because."? I find > understanding an *application* ends up saving questions later. > > "Why do you need to do that?"
My point was that I only needed to know that you wanted to control it from an automatic timer to water plants. That's all I need to know to understand the technical issues. It would be better to explain the requirements in more detail.
>> Of course all power supplies should limit the output power to the load >> to prevent catastrophic failures. My point is you don't need to draw >> this full current when you press the switch. If you did that, you would >> be drawing the PSU down and all other solenoids on the same PSU would >> deactivate. Another issue in using the switch with the full current >> limit of the PSU depends on the current and the rating of the switch, >> but it may well run excessive current though the switch. > > I didn't claim that the switch would cause the supply to hit its > current limit. Rather, that the supply *was* current limited > as part of any reasonable such application.
Then why bother to mention it at all? I find this confusing.
>> BTW, coils are not specified for "inrush" and "holding". They are >> specified for pull in and drop out. These are typically voltages and >> specify the level at which the solenoid is guaranteed to pull in or drop >> out. Coils don't have "inrush" current, that would be a capacitor. >> Coils resist changes in current, so when you apply a voltage the current >> goes up gradually (even if gradually is quick). It doesn't spike up and >> then drop back. > > Excuse me, but the solenoids (coils) used in irrigation systems > *are* rated as "inrush" and "holding" current. That's what you > will find on their "datasheets" when you go hunting for specifics. > You can always be pedantic -- and your end user will end up > calling the solenoid vendor:
I was trying to help in an area where I thought you didn't understand something. Obviously I am the one needing to understand somthing. What is the meaning of the "inrush" current? Does "inrush" refer to the water or the actual current? As I said, inductors resist change in current and do not have an inrush.
> "Hi, could you please tell me what the pull-in voltage is for > the solenoid used on your model ABC irrigation valve? And, > while you're at it, could you please tell me what the drop-out > voltage is? What's that -- yes, these are running off a 24V > system as indicated on the box that they came in... So, why > do I need these numbers, you ask...?" > Speak the language appropriate for the application domain you're > working in. :>
The trouble is that you might not power them from a 24 V supply. It sounds like you are going to add other electronics which may affect that supply voltage. But then this comes back to the lack of complete information supplied so far. It would be very helpful if you can explain more of what you have and what you intend.
>> I don't recall you mentioning an "isolation" barrier before. Where in >> the system is that currently? Is that in your controller? Where do you >> expect to add your electronics? How will the power to the solenoid be >> controlled by the switch? I don't mean the switch sensing, I mean the >> control. Once you sense the switch, how does the solenoid get controlled? > > Currently, the controller just drives the 15 irrigation valves > with a darlington and flyback. No isolation at all -- the > controller is just an SBC from a design I did for a client > many years ago that I had repurposed for this role, temporarily.
So this is not a commercial unit, but a home built one.. that is important.
> *New* design will be expressly for irrigation controller. As such, > outputs will need to be isolated from the "logic", communication > network, power for those electronics, etc. You can expect to > encounter large voltage spikes (lightning strikes) as well as > deliberate attempts to subvert the electronics "inside" that > isolation barrier. > > The user will see a network connection to the controller (which > powers the "smarts"), a connection for "valve power", and wires > running off to the individual solenoids (15+master -- though that > would probably increase as the electronics for an individual > valves represent a small cost). Additionally, connections to > a flow meter and water treatment appliances (basically, just > more isolated DIO's). > > The button is just a button. I *choose* to use it to signal > actions for that particular electric valve. I could just as > easily use it to open the garage door... it just happens > to use the same "conductor" as the solenoid valve. > > (e.g., I will eventually use this to control portions of the > laundry, the hot water heater and the garage door opener -- as > these are all just "isolated DIO applications") > >> You haven't told me enough information to help you. >> >> BTW, this is *not* a difficult design task. I don't think there will be >> a "tough" part once I understand fully the issues involved. > > I think I've already got a flexible solution that should give > me everything I need. I just have to consider each likely > failure (in the field wiring) to verify that I can detect each > such condition. I.e., so I can report problems before they > affect actual operations. (you'd like to know a valve wasn't > operational/controllable BEFORE the plants serviced by it > dried up and died; you'd also like to know that your connection > to the garage door opener was ineffective before you tried to > open it!)
Ok, then good luck! -- Rick
On 2013-09-17, Don Y <this@isnotme.com> wrote:

>> N/O >> -------- +-----o o-------+ >> | New | | | >> | Power |---+---[Solenoid]---+ >> | Supply | | >> | Low V |-----+---[R]---+----+ >> -------- | | >> |<---V--->| >> >> R is high wattage low resistance, chosen to allow reliable >> operation of the solenoid with your existing supply. V > > You are sensing V *behind* the solenoid's resistance -- O(120 ohms). > >> is the voltage developed across R, which will be higher when >> the push button switch is pressed than when the solenoid is >> not shorted by the switch. > > If the switch fails shorted, then the solenoid doesn't work. > This is the same sort of problem Spehro's NC approach has -- the > circuit needs immediate attention (because the solenoid can't > perform its normal function -- even though ONLY the button is broken) > > Also, the solenoid effectively "turns off" when the button is > pressed. So, if the controller does NOT want to turn it off, > it ends up "pulsing" off (while the switch is pressed) and then > back on (after the switch is released and the controller has > decided to "leave it on"). >
put a resistor in series with the switch -=- +----o o--[470]------+ | | 24V ---------------------------+---[Solenoid]-------+ (120) | 0V -----[1.0]--------------------------------------+ B sense voltage at point B above about 210mV is switch pressed, you many want to use a trimpot for the comparison voltage to allow use of different coils how to sense the button when the coil is off? -=- +----o o--[470]------+ A | | 24V ---11K-----------------------------+---[Solenoid]-------+ (120) | 0V -----[1.0]--------------------------------------+ measure the voltage at point A less than 1V is switch pressed. same deal you'll need a pot to adjist the set point to compensate for coil resistance. ( LM339 36V comparitor circa 30c a piece ) or perhaps wire it to a DAC input with 100K in series -- &#9858;&#9859; 100% natural --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On 9/17/2013 1:42 AM, rickman wrote:
> On 9/17/2013 3:07 AM, Don Y wrote: >> On 9/16/2013 11:28 PM, rickman wrote: >>> On 9/16/2013 9:03 PM, Don Y wrote: >>>> >>>> That's the easy part. Tough part is getting the information I need >>>> across the isolation barrier without using anything precious or >>>> "fragile" on the field side of that barrier (cuz you have to expect >>>> a very hostile environment, there). >>> >>> You used some thousand words describing your plants and how you want to >>> water them and I don't think you have really explained the problem well. >>> I don't need to know the details of how you water your plants, I just >>> need to know the relevant details. >> >> You wanted to know why I needed an electric valve. Would >> you have been happy had I replied, "Because."? I find >> understanding an *application* ends up saving questions later. >> >> "Why do you need to do that?" > > My point was that I only needed to know that you wanted to control it > from an automatic timer to water plants. That's all I need to know to > understand the technical issues. It would be better to explain the > requirements in more detail.
I guess *my* problem is that I assume folks have read the other posts in a *live* thread before commenting. As I had already tried to explain why TWO valves were needed (manual and electric), I assumed my response to that wasn't clear and endeavored to be more specific. FWIW, notice how often people reply to a post with a question like: "Why would you need to do *that*?" instead of accepting that the OP *wants* to "do that"!
>>> BTW, coils are not specified for "inrush" and "holding". They are >>> specified for pull in and drop out. These are typically voltages and >>> specify the level at which the solenoid is guaranteed to pull in or drop >>> out. Coils don't have "inrush" current, that would be a capacitor. >>> Coils resist changes in current, so when you apply a voltage the current >>> goes up gradually (even if gradually is quick). It doesn't spike up and >>> then drop back. >> >> Excuse me, but the solenoids (coils) used in irrigation systems >> *are* rated as "inrush" and "holding" current. That's what you >> will find on their "datasheets" when you go hunting for specifics. >> You can always be pedantic -- and your end user will end up >> calling the solenoid vendor: > > I was trying to help in an area where I thought you didn't understand > something. Obviously I am the one needing to understand somthing. What > is the meaning of the "inrush" current? Does "inrush" refer to the > water or the actual current? As I said, inductors resist change in > current and do not have an inrush.
Current. Note it's not just an inductor but actually a solenoid. This is "just how its done" in that industry. The COTS controllers apparently have really wimpy power supplies. And, can potentially be interfaced to other ancillary equipment (e.g., you may need to start a *pump* if your irrigation system is fed from well water; the power to engage that "contactor" for the pump comes out of the power budget of the controller. When "programming" such a controller, you can potentially have multiple "zones" (valves/solenoids) engaged concurrently. So, the homeowner (who often does this without hiring an installer) needs some EASY way of knowing if his "program" can be supported with the power available from the controller for the valves. E.g., I have 15 zone valves, here. Plus a "master valve" that must be engaged for any of the other valves to "see water" (it gates the water supply to the other valves). The zone valves that I use are rated 0.3A inrush, 0.19A holding. Said another way, I need at least 3A to be able to have all of the zones active concurrently (assuming I stagger their turn-on times). If I want to be able to engage all of them with a single control signal (i.e., coincidentally), then I need closer to 5A.
>> "Hi, could you please tell me what the pull-in voltage is for >> the solenoid used on your model ABC irrigation valve? And, >> while you're at it, could you please tell me what the drop-out >> voltage is? What's that -- yes, these are running off a 24V >> system as indicated on the box that they came in... So, why >> do I need these numbers, you ask...?" >> Speak the language appropriate for the application domain you're >> working in. :> > > The trouble is that you might not power them from a 24 V supply. It
The irrigation valve suppliers aren't aware of that. Just like the automobile manufacturers are not aware that you might want to install that big V8 in a *boat*. Or, use it to power a genset. They write their specs and literature from the standpoint of the irrigation controller market. 24V is the standard power supply voltage available for valves. If you want to drive them with a current source, that's your problem. If you want to drive them with a couple of alkaline cells, also your problem.
> sounds like you are going to add other electronics which may affect that > supply voltage. But then this comes back to the lack of complete > information supplied so far. It would be very helpful if you can > explain more of what you have and what you intend.
What I'm pursuing, currently, is a "one bit" high voltage, high current digital I/O driver that is current limited (i.e., so I can put N of these on a power supply that is able to deliver N * current_limit and not worry about the supply EVER being dragged down). Isolated so conditions encountered on the field wiring don't affect the controls (and beyond). Capable of handling individual loads in the ~0.5A ballpark (overkill but probably doesn't add anything to the cost) with open circuit voltages in the ~50V range (though it will probably see 24V max). The input will be a volt-free contact closure -- easy to conceptualize (i.e., a switch -- whether that's a pushbutton or a limit switch in a garage door opener or a reed switch mounted on the garage door track, etc.) Said another way, I should be able to gut a pinball machine (electromechanical or electronic) and use this as an interface to emulate the original controls (though it would be horrible overkill)
>>> I don't recall you mentioning an "isolation" barrier before. Where in >>> the system is that currently? Is that in your controller? Where do you >>> expect to add your electronics? How will the power to the solenoid be >>> controlled by the switch? I don't mean the switch sensing, I mean the >>> control. Once you sense the switch, how does the solenoid get >>> controlled? >> >> Currently, the controller just drives the 15 irrigation valves >> with a darlington and flyback. No isolation at all -- the >> controller is just an SBC from a design I did for a client >> many years ago that I had repurposed for this role, temporarily. > > So this is not a commercial unit, but a home built one.. that is important.
It will eventually be offered for others to copy. Whether someone wants to commercialize it or not isn't my concern. It's just one component in a larger system. But, one that needs to be designed in a way that would make it suitable for others' needs beyond just my own -- including other applications (e.g., the pinball example). And, that doesn't require an engineer to deploy.