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.