Sunday, January 27, 2008
How Salt Systems Don’t Work
From Day One.
There was a Pool Show in town here lately. It was a three day event. Lots of classes. Lots of exhibits. I’m sure a lot of good and sorely needed training got done there.
I didn’t go.
Not to say there’s anything wrong with Pool Shows. But, except for the rare class or two taught by people on the Tech Side of Life With No Monetary Interest In Whether You Buy What They’re Teaching (and you good guys and gals who do that know who you are and we love you for it) the rest of it is just A Show.
But, it’s the only time I ever find myself feeling sorry for Sales Reps. Think about it; standing at a booth all day long, trying to figure out ways to make a black plastic pool pump look and sound sexy. How hard is that?
The reason I bring The Show up at all is that they had one seminar, added to the schedule at the last minute, titled, How Salt Systems Work.
As I said, I didn’t go. I heard, though, through the Pool Guy Grapevine, that in some of the other seminars, those that were water chemistry centric, the main complaint of the folks in attendance was What The Hell To Do About These Damn Salt Systems. Of course, the people attending the water chemistry seminars were the “hands on” folks, the ones who see these systems in the field and try to explain to their customers each day why their pools are falling apart.
But enough about Pool Shows. Let’s talk about what happens when Salt Systems Don’t Work.
Here’s a picture of a salt cell plate that was about three years old when we replaced it.
This is the center plate in a pack of seven plates. This is The Weak Link In The Chain, so to speak. It gets eaten alive by being the return path for all of the current flow. As you can see, it is literally eaten alive. The way it works is that current is applied to one of the Outer Plates in the pack of seven adjacent plates by an insulated conductor. That plate is electrically connected to the outer plate on the other side of the pack by another insulated conductor. Then low voltage, high current is applied to these outer plates. The current jumps from the two outer plates to the next two plates, then in turn to the next two plates, and then, the plates on either side of the center plate deliver their full current flow to it, and it provides a path back to the power supply to complete the path for current flow.
Here’s a basic drawing of what’s going on, using a simpler, three plate pack as an example. Don’t laugh. I don’t use PC Paint very often.
The first plate in the foreground receives current flow from the battery – in our case, a power supply – and it passes that current flow over to the last plate in the background via that heavy dark line, which if you crack open a salt cell with a sledge hammer like I did, you’ll see is an insulated bar to avoid stray conduction to the center plate as the current flows through it. Then, the Magic of Electrolysis occurs. The current flow – up to 8 amps of current – passes from the two outer plates to the center plate through the water. That’s why you have to add some salt to your pool water. Without it, the water wouldn’t be conductive enough to pass the proper amount of current flow.
Part two of why you add the salt is so that, with that big whopping current flow, you zap the inactive chloride ion that got there when you poured the salt into the pool. When you pour it in, the salt immediately dissociated into sodium and chloride. The chloride is just in there, doing nothing, until it passes between those cell plates and the current flow turns it into Cl(little lower case 2), which is an oxidizer, and that Cl(little lower case 2) mixes with the water to form hypochlorous acid, the killing form of chlorine.
That’s where those Salt Reps get off telling you that you only have to add salt once. When hypochlorous acid does its job and kills something, the HOCl (hypochlorous acid) dissociates and that Cl is back to being an inert chloride ion again. Now, the next time it passes through the cell plates, it gets zapped back to life, mixes with some water and makes HOCl all over again.
So that’s true. Once added, you never have to add salt again. As long as your kids never splash even a drop of water out, as long as you never backwash your filter, as long as you don’t have any water features which aerate the chloride rich water, as long as it never rains and dilutes your pool water. Which is why, in spite of the way the Salt Reps twist the science to make it sound like There Really Is A Free Lunch And This Is It… there really isn’t. But you knew that, right? They are, after all, salesmen. What did you expect?
But getting back to why I took pictures of that cell plate. Oh, by the way, for comparison, here’s a picture of what’s left of that cell plate alongside one of the other plates from that pack that was lucky enough not to be in that center, return to battery, position.
When this salt cell failed the only indication we had was that the chlorine level in the pool kept getting lower and lower. Depending on the time of year, you could go more than a couple of weeks before you make the decision to spin the connectors off the cell and take a look inside.
During that time, from the moment that Return To Battery Connection just dissolved away and there was no longer a return path VIA THE SALT SYSTEM for current flow, where was that current flow going? The power supply still had +28 VDC available at it’s output, and the physical connection to the two outer plates was still there, but there was no longer any way for those plates to do their little Jump From Plate To Plate trick and return, finally, to ground.
You see, in a perfect world, current flow follows the path of least resistance. So, on Day One of operation, these salt systems are operating exactly as they did in the lab, when they proved that they were emitting less than the maximum allowed Stray Currents to receive their UL listing. But when the salt cell fails like this one failed, the current flow starts looking for new ways to get to ground, back to battery, as it were. And it will follow any path it can find to get to ground. The more resistance there is, the less current will flow. But when you’re starting with 8 amps, you can still have a pretty healthy current flow when it finds it’s way via other paths to ground.
Paths like: Salt cell plates to bonded (grounded) and very expensive heater. Or salt cell plates to bonded ladder or grabrail. Or salt cell plates to bonded light niche. Or salt cell plates to anything metal that is submerged in your pool. But still you should be safe, right? I mean, that Stray Current flow will go right to ground via the bonding lug, right?
Well, that’s when you get to add in Galvanic Corrosion to the Stray Current Corrosion. Take a pool ladder, for example. Stainless steel mounted into a brass anchor cup set in the deck. Now, splash salt water on it all day every day the pool is being used. The chloride rich water sets up a Galvanic Cell that causes corrosion to form BETWEEN the stainless rail and the brass anchor cup. That presents resistance to current flow. Now, you come along and grab that handrail and you get a tingle. Because you present less resistance to current flow than the corrosion building up in the anchor cup. And when you have that scenario, you go out and Google for:
Salt system conducting electricity on handrails
That showed up on my Site Meter this week. But that’s nothing new. I’ve had lots of hits like that over the last year and a half.
Now let’s take this a step further. Let’s back this scenario up to when the salt cell’s center plate first started to deteriorate. I’m guessing, but from the looks of it, I’d have to say that this plate was in pretty bad shape for over a year. So, for over a year, it wasn’t able to provide as efficient a path to ground as it did when it was brand new, and I’d say that the Stray Currents were ramping up from the minimally allowed level to something that sends people out on the internet Googling for things like:
Pool salt system conducting electricity
How do you troubleshoot a swimming pool heater plumbed with plastic pipe for electrical electrolysis
Stray electric current salt water pools
Zinc anode skimmer basket does it work
“Chlorine generator” “copper pipes”
Dealing with stray currents around pools (from Australia… Imagine that)
Using the old Site Meter info again, in a sample group of the most recent visits, this represents 17.5% of the people who come to my blog via a Google search.
Now let’s take this even a step further. This deterioration of the plate begins the minute you plug the salt system in the very first time. So, it’s a safe bet that the Stray Current Corrosion begins within a few days, weeks, months (?) of your system being brand spanking new.
Every manufacturer admits that your salt cell is only going to last you about 10,000 hours, which under normal use is from three to five years, and the reason why is because they know that from day one, the cell plates are wearing out just like this one did. And my contention is that as they wear out, the Stray Current Corrosion is ramping up.
These cell plates are made of ruthenium coated titanium, which, in the Galvanic Series, is just about the hardest, most noble, least active, least cathodic metal compound around. And still, it disintegrates with current flow. Your brass and copper and stainless steel pool components don’t stand a chance.
Another thing that makes me think I'm on the right track here is something I remembered reading in the Save-T 3 automatic pool cover owner's manual, on page 13:
"Since 1999 when Underwriters Laboratories (UL) dictated that all metal components of automatic pool covers must be bonded to the pool grid, we have seen an increase of galvanic corrosion [emphasis mine] on some of the aluminum components. In addition, the popularity of electric chlorinators where salt is added to the pool water has increased."
Here's the link. It's a slow loader, but it does work.
What that's saying to me is that, as the salt cells age, and as they emit stronger and stronger stray current, we see more and more corrosion in any metal that's bonded to the pool grid, as that stray current seeks a way back to ground. Like the pool covers; the incidence of corrosion INCREASED after they were required to be bonded to the pool grid.
Anyway, that’s why I wanted to write a blog piece about How Salt Systems Don’t Work, because I’m sure that none of this was brought up in that industry sponsored seminar, How Salt Systems Work.
So, the next time one of your customers asks you, "Didn’t you just replace that (fill in the blank with your favorite salt damaged component) a couple of months ago?", just print out this blog piece and hand it to them and say, “Yes, and here’s why we’re going to do it again real soon”.
Unless, of course, you sold them the salt system, too. Then you’ll just have to do what everybody else is doing; shrug your shoulders and pretend that you don’t know what’s going on.
Good luck with that.
The plate design you show in the diagram is inexpensive and not used in most higher-end saltwater chlorine generator systems (SWG). Instead, a bipolar design is used which has two main plates connected to the voltage source and has additional plates in between these two plates and these are not connected to any external voltage source. The net effect is that for the same voltage and size of cell, a much smaller external current results passing through each plate (so is less damaging to each plate), but since there are multiple plates there is a high production of chlorine (and hydrogen gas). It essentially behaves like a series of electrochemical cells with a lower voltage drop in each cell (the sum of these voltage drops equals the higher voltage that is applied externally). It is also technically equivalent to hooking up multiple cells in parallel to a lower voltage external source.
If there is any stray current then it should be very easy to find by simply measuring the current accurately at each end of the SWG cell -- that is, the current in the positive wire and the current in the negative wire. If these are not the same, then the difference is a stray current.
So Pool Guy help me understand this. I was at the largest Home and Landscape Expo in Northern California a couple of weeks ago talking with representatives of the Pool and Spa industry. I came away very confused and hope you can help me understand all those numbers that spill out of the salt reps mouth about what levels of salt does what to the pool and equipment.
Like it takes 6000 ppm of salt to cause any type of corrosion and since their system operates at a very low salt level of 2500 ppm there is no way their system could cause any corrosion.
And just what is the taste level of salt in water?
Then I was told by a pool builder that they have the perfect system for sanitizing their pools. They just install an inline chlorination system, and then they install a FROG mineral system so they don't have to make as much chlorine and then they install an ozone generator to make sure they kill everything (except it doesn't). Sounds like a lot of work, alot of pool chemical management and lot of refillable products to continue to buy to try to get the job done.
What say you?
Actually, the plate is from the cell of the largest selling salt system on the market. It is comparably priced to any of the Big Three. In fact, it is one of the Big Three. Further, when I disassembled the cell, there were 7 plates in the exact configuration that I showed in my simplified diagram, which I stated was a simplified diagram. Anyway, that's that.
I'd like to know who told you that the design I depicted in the diagram isn't what's used in most "higher-end" systems. Can you shed any light there? The reason I ask is that I've never been able to get any electrical diagrams of any of the salt cells. They're not in any of the manufacturer's literature and they're not even readily available to the warranty stations, as the cell isn't repairable, so no diagrams of it are provided. If you have any, I'd really appreciate it if you'd send me some. I'm sure you didn't make that statement based solely on something someone told you.
The lack of electrical diagrams is why I took a sledge hammer to this "higher-end" cell, so that I could get inside and see how it was physically connected, and the diagram shown is how it was connected, less four plates because I couldn't draw them with PC Paint without making the whole drawing just look confusing.
So, anyway, this system that I took apart wasn't acting like a set of parallel circuits. It was acting like A parallel circuit with a common return, in that you need two legs to call it a parallel circuit.
As far as your argument that the current just doesn't exist if the return path isn't there, that would be true if these were like the electrolytic cells in your car's battery, all encased in a rubberized plastic container that completely insulates them from ground (infinite impedance). But instead, they are electrolytic cells in a twenty thousand gallon container of electrolyte - the salt pool. If the voltage is available at the outer plates, the current will flow. If the previous path of least resistance - from plate to plate to plate to ground - is broken, then it will flow to the next path of least resistance, which would be any of the metals bonded to the pool's bonding grid. Granted, it will be significantly less than the 8 amps max that these systems are capable of running at, because there will be a lot more resistance in getting to that alternate path, but it doesn't need to be a lot of current flow to do the kind of damage that we routinely see on salt pools. That is, in fact, the definition of stray currents. So, as the cell plates degrade, the other paths to ground in the electrolyte receive more and more stray current flow.
Go to the label Builders Problems With Salt and scroll down to the blog piece "Stray Currents Are Still Dissolving Your Salt Water Swimming Pool, Part Three". The builder I quote there talks extensively about stray currents. He refers to it as stray voltage and in the measurements he gives, he talks in terms of voltage. But that voltage will induce a current flow.
I get the point you're trying to make by flatly stating that there are no stray currents and that if there are, they should be easy for me to prove. But I've got an extensive collection of e-mails from you stating just the opposite, that it would be difficult and would be best if special test equipment and special test probes were used.
My counterpoint is that salt pools exhibit signs of stray current and galvanic corrosion and non-salt pools don't. It is my position that it is up to the manufacturers to prove that it's not happening by conducting open, unbiased testing on test pools where salt systems and the types of metal components we're seeing problems with installed on those pools, and that this testing should be done by a third party.
When everything points to the salt and the salt systems as being the culprit, why don't they have to prove that it's not?
But you know and I know that we're both just taking a piss in hyperspace here. They're not going to do any further testing. The oly time they even pretend is when a reporter gets them in a corner, like they did last year when Pool & Spa News was asking them about the stone damage, and they said that "a group of 7 manufacturers" were going to conduct in depth testing and release those results later that swimming season. That was a year ago and since everybody stopped writing articles, they stopped the pretense of researching the problems.
And nothing in the world would make me happier than to be proven wrong here and for them to release real, peer reviewed research. And the reason I would be so happy because I know that I'm right. And any true research would prove that.
For the sake of full disclosure, I need to tell everybody that you're sort of a Salt Rep. Zoeebart reps a salt system that uses a container of salt and through the process of electrolysis makes chlorine and then slurries that chlorine into the pool. It doesn't need for the pool to be saline for this to happen. It's just like the old Uni-Chlor, except that Zoe assures me it doesn't blow up like the Uni-Chlors did.
I had to out you there because otherwise, when my answer plays into your hands as I jump up and down about the saline pool salt reps still telling the same tired old lies about 6,000 ppm and about the level of taste, and then when I jump up and down and tell everyone how silly it is to use the mineral system and the ozonator when it's really just the chlorine in the tab feeder that's doing the bulk of the job of sanitizing your pool, then people who know you're a sort of a salt rep would write in and say I'm playing favorites.
And I will admit that you're my favorite Salt Rep, which isn't nearly as dubious a distinction as you would think. Good luck and remember; Keep Bashing The Salties!
to see a discussion of the bipolar cells I'm talking about. The thread all started because we couldn't figure out how a high voltage but lower current was producing so much chlorine since it was more than a calculation using current through the wires would indicate. What was missing was an understanding that the higher voltage was essentially "split" among multiple serial electrochemical cells. Anyway, I don't know the manufacturers and their designs other than what was discussed in that thread so if one is using the design you showed then that's what they do, but it's not considered to be as advanced as bipolar cells which are more efficient and supposedly last longer (probably because they conduct less current per plate).
As for current leakage and lack of a return path, I talked about that in the following two posts a long time ago:
Note that in the second post I also talk about the conductivity of a salt pool with 3000 ppm salt. The diagrams show that IF there is some current leakage outside the system then if this hits the grounding system it can be serious and I do calculations on that. But if there is such a leakage, then that would show up as an imbalance between the current in the two conductors leading to the salt cell. It makes sense that this would have to happen since the current has to get shunted somewhere since some of it is taking a different path and if all the current isn't in the cell, then some of it most go somewhere else. I suppose it's possible for an equal leak on both wires to occur but that would be weird.
The measurements of voltages is an entirely different thing and is what I wrote to you about quite a while ago. Stray voltages can come from numerous sources and are partly a result of how the electrical distribution system works in terms of the neutral ground. So to test that stray voltages, which are quite real, are coming from an SWG as opposed to an electrical distribution system, you'd have to measure the voltage (between the pool water and some other point such as the grounding system or rail or the ground near the pool) and then turn off the SWG, and measure over about a week to see if it drops. The pool is like a huge capacitor so if the SWG is a source of the voltage, it should drop when turned off. If you turn it back on and the voltage goes back up and this is repeatable, then you can point to the SWG as the source of stray voltage (which would cause stray current).
My gut feel is that the source of the stray voltages is probably external and not related to the SWG, but that the higher conductivity of the pool water (due to the higher salt content) makes that path have more current and that can cause more current in the grounding wire. It is possible that the SWG leaks current, but that would need to be proven by either of the two methods I described (current difference between wires to SWG or voltage change in pool when SWG is on vs. off over a period of time).
And, I must say as I was reading thru the blogs, I had a real appreciation for the enormous amount of reference material you provide your blog readers to back up your statements.
And by highlighting the water issues around the country, we can begin to see how fragile things really are in the U.S. The city of Dixon will again be addressing their water issue in March or April and water issues have stopped several housing developments from completing their project. And Georgia is thinking about closing their swimming pools.
Do you think swimming pools will go the way of the wood burning fireplace in California? Restricted Use?
And by the way slurry sounds so-so tarry like slurry seals for a road. I like to say that it is gravitational forces of the planet that delivers the solution to the water/or the chlorine is gravity feed to the pool water. Which also means you don't need to run the pump to make it.
I think the big picture is being missed here. Occam's Razor essentially says that the simplest explanation is usually the correct one. The simplest explanation has nothing to do with stray currents from the SWG, but rather from the fundamental physical fact that conductivity is approximately proportional to TDS. Any electrochemical (or galvanic) metal corrosion will be accelerated in water that is more conductive, period. The issue isn't whether this occurs, but rather the degree of the problem and whether it can be mitigated. The TDS or salt level is just one factor -- the chlorine level is another factor and whether CYA is used.
For example, when I asked my PB a while back whether he noticed any corrosion differences in his SWG pools vs. non-SWG pools (and about 85% of his new installations are SWG) he said that the only noticeable issue was with the electric pool covers whose leading edge metal bars were in the water (so that they "vanish" when open) and that this was mitigated by the pool cover people by using a zinc block connected to the bonding wire. He said the problem started to show up when it was required for this metal bar to be connected to the bonding wire and that the zinc blocks need to be replaced more frequently in SWG (salt) pools. Since these metal bars are aluminum, it's not surprising that connecting them to the bonding wire would promote galvanic corrosion relative to the mostly stainless steel components and that this occurs more rapidly in the higher conductivity of salt pools.
The most extreme example of corrosion reported on pool forums is with indoor pools using an SWG and not using CYA with chlorine levels in the 3-5 ppm FC range. Not every pool in this situation shows corrosion as rapidly, but there were more reports of this than any other. The corrosion was with stainless steel components. Again, the simplest explanation is not that this has to do with the SWG itself but rather a combination of high disinfecting/oxidizing chlorine levels due to no Cyanuric Acid (CYA) and higher conductivity and chloride concentration from the salt. Though the salt level may be 2-6 times higher than in a non-salt pool and therefore conductivity roughly 2-6 times higher, the oxidizing power of the chlorine is 30-50 times higher than found in a typical outdoor pool using CYA. So it is pretty obvious that this particular problem can be mitigated by using some CYA and that this will help independent of the salt level (and yes, the higher salt level will still corrode faster, but if this is skewed out to many years then the problem is essentially mitigated).
As for stray voltages that are measured, the following link describes this phenomenon including links to other sites:
If there are such voltage differences across pool surfaces or along the bonding wire, then there can be stray current. Higher salt levels in the pool mean higher conductivity so if the bonding wire gets broken or corrodes (most likely at joints of dissimilar metals), then these stray voltages would generate current along the next "most conductive" path which may be through the pool water which can lead to corrosion of metal in the water.
Where you and I disagree is that you want to ban salt pools completely whereas I want greater disclosure so that these issues can be mitigated. My local pool store says that most non-salt pools they measure have TDS in the 750-1500 range; some lower to 500, some higher to 2200. Obviously, this will differ depending on type of filter (whether backwashing is done) and whether winter rains dilute the pool water. There should be simple disclosure that the higher salt level in SWG pools means higher conductivity which increases the rate of corrosion, period. The question is whether this becomes fast enough to be a problem and if so, how to mitigate it. A zinc block on the bonding wire might be one solution, especially for the more extreme cases such as the aluminum leading edge bar in "vanishing" electric pool covers though just doing this as a preventative for any SWG pool would probably make sense (in fact, for non-SWG pools as well, just to minimize metal corrosion overall even in cases where stray voltages are present). The use of CYA in indoor pools is clearly another way to mitigate problems. Sealing stone or using less porous or fired stone is a way to mitigate that problem (especially in those areas where the evaporation rate and salt deposition rates are closely matched without rains for dilution).
Pools are corrosive environments, starting with the fact that there is water with dissolved oxygen, adding to that the high oxidation power of chlorine, and adding to that the higher conductivity at higher TDS (salt) levels. No one uses plain steel even in non-SWG pool water. Just as corrosion was minimized in non-SWG pools by using stainless steel, so too corrosion can be minimized in the "bond everything touching the water" environment by using a sacrificial zinc anode block.
It was in the post Lying Liars, which you can find in the Environmental Impact label. I quoted a letter from the Boss of the Salt Institute. Here's a cut and paste of what I said, what he said and the link:
The Salt Institute, a group that represents 36 foreign and domestic salt producers, admits you can taste salt at levels even lower than 250 ppm.
“The secondary drinking water standard for chloride is determined for taste and established at 250 mg/L. If 100% of the chloride in a particular drinking water were in the form of sodium chloride, water containing 250 mg/L chloride would contain 160 mg/L sodium. Thus, 160 mg/L would be the appropriate level where people would notice the taste of sodium chloride.”
Remember, this is from the Salt Institute, the lobbying arm of the salt industry.
And thanks for the update on what's happening in Dixon. I didn't know that. I'm working up another environmental piece. I've been saving stories about the environmental impact of salt from around the internet for awhile now. I think, at the end of the day, that's how they're going to sink the Saline Pool guys. When the municipalities start telling folks that their pool water is classified as toxic waste due to it's high chloride content and they have to pay a surcharge to dump it, I think there'll be a waning interest in salt systems for swimming pools.