Another way to create mounting plates for control panels
pmrobert
Posts: 669
After arduously fabricating numerous metallic plates for control panels in the past I wish I had thought of or knew of this technique of designing them out of 3.2mm PCB.
Comments
I usually don't have big panels like that, but it does make sense. Fiberglass laminate is tough stuff. It looks like your panels don't have copper on either side. Do you sometimes include that for a ground plane?
I do use smaller stock enclosures, and when possible, plan the main circuit board (0.062") so that it takes advantage of the included mounting locations.
@Tracy Allen, I personally have not used this technique but it's very much in my armamentarium for future commercial projects. I have been using .080 or .100 aluminum and fabricating the mount as needed (quite time consuming). For non-commercial projects I can use PVC cabinets. I cannot use PVC in industrial for several reasons such as fire safety, non-industrial temp rating, etc. For example I have replaced a pricey residential pool controller with a RaspPi based cabinet - ~$300 vs $8K. I am currently iterating through the final design for a Prop based air compressor controller and will post that project when it's complete. The compressor controller will easily fit in a small project box and replace a troublesome pressure switch and tank drain. Being able to configure tank pressure via a web page is very nice and saves energy. Anyway, I digress as usual... Back OT I absolutely plan on using FR4 laminate with the next commercial job and will report back. The copper backplane is likely unnecessary in these applications as the usual use would be to mount DIN rails, wire duct, etc. The logic level component(s) are usually self contained and mounted on DIN rail. Image of pool controller attached, this controls the pump motor, heater, pool lighting, spa blower, salt water chlorinator controller, solar panel circulation and reports/records various system pressures, temperatures, voltage, current, energy usage, status, etc. with both SQL and MQTT data stores. Wifi connected currently, I do need to add a physical control interface in/on the box to facilitate servicing the system without a phone, etc.,
@pmrobert ,
Are you willing to share your schematics and code for your salt water pool controller?
Jim
Yes! I just have to create them - that's the tough part oddly enough. I have numerous hand drawn schematics of each of the individual outputs and outputs. The actual logic and interface is on an RPi4 under Node Red, a Node JS based "Low-code programming for event-driven applications " environment. The salt water part is really simple - I'm using a CircuPool Edge standalone controller and cell - I provide it power via a contactor and it does it's thing at what ever duty cycle it's configured for. The very expensive Hayward controller that was running everything decided to let out a LOT of magic smoke (~$6K worth) so that was the impetus to DIY this. This all OT for a Parallax forum so if the mods wish I'll take it private. My upcoming air compressor controller is definitely Prop based and I'll be sharing all that as it happens.
Mike
This is the last version of the cabling sheet - it's not correct as I've taken the house water pump pressure sensor and contactor control out of this system and have disabled the solar heating sensor and control valve as I'm currently redoing the entire pool plumbing system as the water is warm enough to swim in currently. I also just last week replaced the two speed 1.5hp pump with a 2.0hp variable speed pump. Early indications are power usage is down 50%+. Love the VFDs!
Thanks Mike,
I will print out your spread sheet and study it. I think that it might be adaptable to a P2. I am only using the controller to start and stop the pool pump and make chlorine. I will need the flow sensor, temperature sensors. I wish I could find an inexpensive way to sense PH levels as I have to constantly add Acid. and with a sensor, I could use a peristaltic pump and automate it. Would also be neat to add water level sensing.
Jim
@RS_Jim - The pH sensors, as you know, are pricy, need to be recalibrated, etc. Perhaps @"Tracy Allen" has some ideas on this. I'm fairly certain he is very familiar with water quality sensing, etc. The water flow sensor I'm using is https://www.amazon.com/gp/product/B07MY6JHNR/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&th=1. It emits 6 pulses per liter so is relatively very easy to read. I purchased a peristaltic pump a couple of years ago, will likely eventually figure out a way to use it. My pool would probably do well with ~100ml HCl daily to compensate for the NaOH the chlorine electrolytic cell emits as it produces chlorine. Side note: I use a peristaltic pump on a 15 gallon tank of 7% H2O2 to inject a few ppm into my house water at the well pump discharge and it works phenomenally well at cleaning up the ground water which has H2S and some tannins in it. It's wired to the pump so it only runs when the pump is on.
Mike,
how did you arive at the 100ml number?
Jim
Hi Mike,
About pH, definitely use an isolation buffer between the sensor/hi-Z amplifier and the rest of your control system. Same goes for ORP or any sensor that relies on wet chemistry. The sensor itself, I don't know if there are ones that are special for saltwater pools, but generically it needs be one with a flat, easy-to-clean surface, meant for the field rather than for the lab beaker.
Wow it's great you have a salt water pool. I love to swim, and am lucky to have a large outdoor community pool for laps a couple of blocks from home. It's a standard chlorination process. I've heard about salt water pools but had to look it up to educate myself about the levels of salt and the chemistry involved. Of course, from an engineering perspective, I wanted to know how the Chlorine Production Unit (CPU!) is built and driven. How about DIY? I found the references to the DIY units built by NGOs for use by remote communities. Like this one from a Christian NGO, referenced on Instructables.
https://www.instructables.com/DIY-12-Volt-Chlorine-Producing-Unit-for-Water-Puri/
The NGO apparently sells the exotic electrode meshes, one of titanium and one with a ruthenium (platinum group) coating. Another reference links to an MIT class project that uses graphite electrodes (salvaged from old carbon D cells).
http://eburn.scripts.mit.edu/pened/lib/exe/fetch.php/lessons/waterchlorine/chlorine_final_report.pdf
Observation and anecdotal - I record the amount of HCl I add and it works out to right around 100ml per day. I do not add 100ml/day, I add HCl when the pH exceeds 7.8 and adjust to 7.4. It varies, 100ml/day is a very rough mean average. I would like to add a pH sensor to the system - then I would have data to eventually calculate HCl top off required. Acid requirement seems to be inverse of the CPUI set output - if it's making Cl it's also making NaOH. I also have the variables of occasional considerable precipitation (I'm in South Florida) which washes out the existing pool water along with the stabilizer (cyanuric acid) so the always certain solar UV eats the Cl like i eat a nice Mahi filet. :-) Several variables. Also, water temperature plays into the equation.
Mike
Very interesting!
The salt water concept is very nice. No more transporting the pool store's liquid chlorine solution once a week or so! I believe the commercial units use ruthenium coated titanium plates ($500 per cell!) and alternate the polarity every 30 minutes or so. The expensive one that came with my house (I've been here for 7 years) recently decided to smoke itself. Prior to that it did report the cell's voltage, polarity and current. ~23 volts and 7.x amps was the norm at 2700 ppm NaCl concentration. The purpose of the polarity reversal is to prevent calcium, etc., deposition on the plates. I do believe DIY is definitely attainable. I still have the old cell and plan to play around with it. I've already acquired a digital variable power supply (max 30V, 30A) for this. I'm very glad you chimed in on this. Can ORP be converted to pH reliably? I've found conflicting info on this. Also - that MIT paper is very intriguing! Thank you.
@RS_Jim - here's the chemistry as to why the HCl requirement changes over time. Since the Na+ ions are still out there after dissociating from the Cl- the hydroxide Na at the end of the reaction seems to recombine with the Cl after the Cl has oxidized "stuff" so in theory the NaCl level in the pool should reach equilibrium theoretically creating a very nice closed loop system fed by the electrolytic cell. That's not the way reality is however - washout from precip, etc., sends the salt somewhere - I still haven't figured out where my pool's overflow drains to! A 40# bag of salt every 3-4 months is much less expensive and far more convenient than schlepping gallons and gallons of chlorinator every week.
Chlorine Generator
Inside the chlorine generator, chloride ions are converted to chlorine gas via the process of
electrolysis. The chlorine is needed to produce hypochlorous acid (as shown in equation 3),
for disinfecting the pool. The net reaction inside the chlorine generator is:
2Clˉ(aq) + 2H2O(l) → Cl2(g) + H2(g) + 2OHˉ(aq) (1)
This reaction raises the pH of the water, as it creates hydroxide ions.
@"Tracy Allen"
Hi Tracy,
As you can tell by my discussion with @pmrobert I too have a salt water pool. I am very fond of it as chlorinated fresh water leaves my skin very "itchy" whereas I don't have that issue with a salt water pool.
Mike, thanks for the input on the derivation of your acid requirement.
Jim
My understanding is that Oxidation/Reduction Potential (ORP) sums up from every moiety in the pool. There is the free chlorine component (Cl gas but mostly as HOCl and OCl-) as well as the hydrogen ion (pH) component, as well as the the sum of all the gunk in the pool. ORP is the "sanitizing" potential. The gunk is mostly on the reducing end of the scale, so as it is oxidized by the chlorine, the ORP millivolt reading decreases. In the process, the free chorine is itself is reduced back to Cl-.
The gunk is from sweat, urine, fecal matter, bacteria, viruses, oils, sunscreen etc.. Gunk becomes chloramines that give indoor swimming pools their characteristic unpleasant oder.
I used to have salt water aquariums and the ORP was the gold standard in "not killing your inverts, fish, etc." . Those ORP probes required constant cleaning and recal occasionally; they were the glass electrode version. Would something like the attached sensor be more what I'm looking for? Luckily we have no chloramine stench mostly due to low pool traffic I would guess.
https://www.mscdirect.com/product/details/10165983
Not sure about that one, as I don't see a close-up diagram or photo of the tip. The kind I do like have a flat end surface, rather than a glass bulb protected inside a rather inaccessible well or shield. The ones with the flat surface claim to be self-cleaning, in the limited sense that they fair better in a process that offers significant flow across the surface. I guess pool monitoring would not be as challenging as, say wastewater treatment, but the benefit can be seen in any application where the pH or ORP sensor is left in place 24/7 for process monitoring/control, as opposed to occasional or short term dip sampling.
For example, see the http://Sensorex.com S272 series, or the S651 series.
I don't recall ever swimming in a salt water pool, but it sounds very appealing. When I first heard about them, I assumed it was basically like, or actually, ocean water in terms of the level of salinity. But no, for what we are talking about it has about 1/10 the salinity of ocean water, right? And electrolysis of the salt generates the chlorine. I don't know why that pool would be less irritating to skin, but I've heard that is so. I think a lot of irritation originates from the chloramines that are the byproduct of sterilization.
All in all, I prefer to swim in the ocean surf, at a warm wild beach, when I get a chance!
Yes, there is nothing like real ocean water for sure! The salt water pools are generally 2300-5000ppm so, yes, they're roughly 1/10 the salinity of ocean water. The pools are right at the edge of perception regarding taste. It seems like that small of a concentration wouldn't do much yet it absolutely does. I've never had an issue with chloramine, you can't even tell the pool is sitting at 4ppm. I've made it very clear - don't pee in the pool! Also used in this pool maybe every 18-24 months is boration. I administer ~30# of borax at those times. It's cheap, it works, I don't measure it and it definitely gives the water a very nice "feel". I'm not sure what the chemistry on that but it definitely makes the pH and Cl levels "smoother" as an anecdotal story. The sensor link you sent me is exactly what I was looking for, thank you. I'll keep reporting in this thread as I reach my desired end result. Next in line, likely today, is a flowmeter. Data is good. Oh, also - the electrolytic chlorine generation does generate a lot of H2 - it's not soluble in water and I know when the cell is powered as bubbles are very evident in two of the return jets. Thank again, more to follow. One more question: where can I find info on TDS reading vs salinity? I know they're not the same but are related. I've got the boron salt, calcium and magnesium in the water in addition to sodium salt. The salt water cell manufacturers are tight lipped on info like that. I asked a couple of days ago and was told "proprietary, we don't release our algorithms or code". It may be time to go on a patent hunt...