Salt Cell Failure - Post-mortem with pictures

[DeadAquaRite]

My salt cell decided to up and die after 9 years, so I decided to find out a) what causes it, and b)if it is repairable.

For those who are too impatient to read to the end the answer to B) is Yes and No. Yes, it is *easily* repairable. No, because the cells have been designed so as make them non-serviceable. Quite frankly this makes me a bit perturbed as it makes ABSOLUTELY no sense to spend $500 when a $50 repair will suffice. Now, on to dissection.

EDIT: Apparently the forum crams all new posts together, so this may get a little hard to read:

The salt sell as it was removed. It was provided by the pool builder, and has been in service since summer 2007. The seam underneath the label is melted or welded together, and survived quite a few sharp blows that I was hoping would cause the seam to fail.

Cover removal is accomplished by flipping the unit and slipping a screwdriver into the gap. It simply snap over a plastic pin (bottom center) and comes off easily.
The black substance on the left hand sensor is hard, apparently some type of epoxy. The black stuff at the top, which can be seen running, is like cooled tar and can be dug out as we will see shortly.

The tar dug out, revealing three screw on connections. Two black (cathode) and one white (anode), with the blacks jumpered together. These correspond to connector pins 1,3 and 2,4 as seen with the connector facing you. Red and blue connect to pins 8 and 10.

 

[DeadAquaRite]

The cell cut open. Only plates 1, 7, and 13 are connected. 2-6 and 8-12 are simply held in place by the plastic guides. These plates correspond directly to the connections seen above.

Visible on the bench are the 10 loose plates. As you can see, they show VERY LITTLE evidence of erosion and no evidence of scale or calcium buildup.

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It quickly became apparent that the edge plates were held fast, while the center plate was loose. It pulled out easily to reveal the contact post had corroded in half.

Note: This cell failed suddenly after 9 years of perfect service. Obviously at some point the contact post (which appears to be brass) separated because of galvanic corrosion. Not really a surprise as the anode only has one connection, while the cathodes have two.

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Looking down into the cell (plate guide removed), you can see what remains of the center post.

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A close up of the failed center stud. Plate erosion is minimal.

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Comparing a good edge post with the failed center post.

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And all three plates together

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The full set of plates, in the order they appear in the assembled cell. Again, note almost ZERO erosion on the unconnected plates, and only minimal erosion on the cathodes.

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And finally a close up of the "active" plates next to the "passive" plates. As you can see, actual damage to the plates is minimal.

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And the tail edges of the previous image

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The housing with remaining anode post and cathode posts removed

 

[Divin Dave]

This is interesting.

Thanks for taking the time to write it up and post all of the pics. you did a nice job of it.

 

[DeadAquaRite]

This is interesting.

Thanks for taking the time to write it up and post all of the pics. you did a nice job of it.

Thanks. In my opinion, there is absolutely no reason for these cells to be non-serviceable. Even if the entire plate assembly had to be recycled/replaced, the tail cap should come off, three nuts removed, and the plate assembly drops out. Re-insert, reassemble, carry on. The initial cost of such a housing would be more, but the guts could be replaced every few years for a small fraction of the cost of a disposable unit.

After 9 years, there is almost observable no damage to the plates, and the cell was performing perfectly until it up and quit. In fact, the only place where noticeable erosion exists is where dissimilar metals are joined, so I suspect the failure is not use but galvanic corrosion. If so, the design should be correctable with a sacrificial anode.

I suspect a large number of these cells are failing because the "anode"(1) stud separates, as mine did. If the case were not sealed, I would have acquired several "dead" units and salvaged plates to make mine workable again.

In a nutshell, I am of the opinion that we are getting fleeced on these cells because a sealed design makes for a larger profit margin.

Philip


(1) I have not checked the schematic and seen which is anode/cathode.

 

[nlindelldc]

Thank you for doing this, I find it to be highly interesting. My first thought after initially perusing is to wonder if it's possible to somehow incorporate "sacrificial anodes" into the SWG like they do on saltwater boats, etc. The idea being that the salt attacks the anodes and are meant to wear over time otherwise leaving them important parts alone.

 

[woodyp]

Is it possible to tell how much if any of the special coating on those plates has degraded/worn off/used up?

 

[DeadAquaRite]

I have no way of knowing. But I can state they showed no loss of performance prior to failing suddenly.

Another interesting thought. This was a T-cell-15. It had 15 plates. I have a feeling other T-cell-N cells might have N number of plates, with the 3 having only fixed plates. Can someone chop up an old cell to confirm?

At $499 for a new cell, these plates are $35 each, max. Thats $105 for a rebuild kit vs $500 to toss it into a landfill.

 

[woodyp]

I just assumed the degradation of the coating on the plates determined most cell death times.

Sent from my XT1030 using Tapatalk

 

[DeadAquaRite]

I just assumed the degradation of the coating on the plates determined most cell death times.

Sent from my XT1030 using Tapatalk

That was my understanding, until this. But mine was going strong after 9 years, and was killed by a corroded leg. That seems to point away from any coating thickness issue. Furthermore, coating failure would degrade over a period, which doesn't describe what people report with cell failure. It is sudden.

Anyone wishing to test for my failure can run a probe down the exit port and test between panel 1, middle, and last. The outside plates should have continuity to pins 1 & 3, the middle to pins 2 & 4.

 

[JoyfulNoise]

Well, I would actually say that the center plate is much more degraded than the edge plates or unconnected plates. The discoloration of the black coating (ruthenium oxide with possible other transition metal catalysts) is important. As that coating begins to wear down and fail, the voltage needed to cause the chlorine generation reaction will increase. Once the coating wears down, other side reactions (especially the electrolysis of water) will start to dominate and the plates will further erode and the coating will degrade. The good news is, the plates are made out of a titanium metal base, so you don't have to worry about titanium contamination in your water. Titanium will oxidize rapidly into oxide particulates which your filter will take care of.

Still a very well documented post-mortem. Thanks for posting this!!

PS - As frustrating as it is, it makes sense that the vendors make these units non-serviceable. There would be no profit to be made form selling service kits. As well, given the long life of these cells, extending that life with a service kit would only result in money lost to the vendor by not being able to sell you a new unit. The SWG market is already starting to be flooded with cheap units (Intex) and so the profit margins are shrinking considerably.

 

[DeadAquaRite]

As that coating begins to wear down and fail, the voltage needed to cause the chlorine generation reaction will increase.

Yet, I have not experienced voltage increase, performance decrease, or current rise. That should have begun several years ago.

And while I cannot measure the plates, what I see predominantly is corroded brass.

As Gillette (and the printer industry) have proven, give away the housing and sell low cost/high margin refills.

 

[JoyfulNoise]

Just to amplify my comments a bit, I happen to have quite a bit of experience with electrochemistry (too many years spent in a metals plating laboratory). If Hayward "wanted" to make a better design, they would do a more rigorous job of shielding the contact point and connection lug from the electrolytic solution. The greatest voltage drop and current density point at the anode and cathodes of any electrolytic cell occur at sharp point, corners, edges and points of immersion (contact meniscus). In some cases, a raised sharp point can a large fraction of the the current density of the entire cell. This is why in electroplating you spend a lot of time obsessing over cell geometry and anode/cathode configurations as the uniformity of the plate can severely limit your plated film quality. Now electroplating is very different from electrolysis BUT the principles involved are similar.

Those contact legs should be shielded from the pool water and sealed as much as possible. That eroded lug, in it's later years of service, was probably carrying a significant fraction of the current in the cell as the gradient of the electric field distribution around it was probably very steep. These cells could certainly be designed much better but I suspect Hayward/Pentair/etc really don't care about maximizing the cell life with a better design

Yet, I have not experienced voltage increase, performance decrease, or current rise. That should have begun several years ago.

And while I cannot measure the plates, what I see predominantly is corroded brass.

As Gillette (and the printer industry) have proven, give away the housing and sell low cost/high margin refills.

That would be very disconcerting if they used brass (Cu-Zn alloy). My guess, depending on how they deposited the catalyst films is that the Ti plate may have been coated first with titanium nitride (TiN is golden colored and conductive) and then coated with the various oxide materials...but that is just a guess based on my other life as a vacuum thin films coating "expert"....

 

[pabeader]

Actually, unless you made a habit of checking your readings regularly and while the cell was actually generating, you probably would have no indication of the slow changes over time.

Why can't you rebuild it? Just have to reseal it, right?

 

[JoyfulNoise]

Actually, unless you made a habit of checking your readings regularly and while the cell was actually generating, you probably would have no indication of the slow changes over time.

Why can't you rebuild it? Just have to reseal it, right?

I think the Aquarite units output current/voltage readings. However, the Aquarite would only display the aggregate voltage and current across all plates. So if one plate was experiencing a higher voltage drop, the others would probably decrease and the total would remain the same. These power supplies typically operate at a constant voltage and then limit/control the current delivered to the plates.

 

[Divin Dave]

Making the cells service friendly is not conducive to sales of new ones.
It's as simple as that. That's just the way business is.

And if it were indeed serviceable, the prices on the parts would be excruciatingly painful.

 

[pabeader]

They do. I have one. But you have to press buttons to get the V and I readings.

 

[JoyfulNoise]

They do. I have one. But you have to press buttons to get the V and I readings.

Yeah. With the Pentair ICs you need a special magic wand to grab the wireless signal and display it to a laptop. Kind of annoying but I guess that's how they maintain The Wizard Oz mystery about it....


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[pabeader]

Wish I had one of those!!

I still think that cell can be repaired and put back into service.

 

[JoyfulNoise]

Wish I had one of those!!

I still think that cell can be repaired and put back into service.

But he chopped it open with a hack-saw....my glue skills are about kindergarten level, maybe yours are better


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[JamesW]

The T-15 has 13 plates, not 15. Cells typically only have 13 or 7 plates. In some models, the smaller cells have 7 plates. In other models, smaller cells have 13 shorter plates. Essentially, the 13 plate models, are two sets of plates, whereas the seven plate models are just a single set.

The voltage for the AquaRite is fixed. There are two outer plates per set and five inner passive plates per set. For the 13 plate models, the center acts as an active end plate to both sets. The number of plates per set and the spacing is the same in all models due to the voltage needed per plate.

The pictures look like some plates have lost most of the ruthenium oxide coating.

The AquaRite salt reading is calculated from the cell performance. As the cell begins to underperform, the salt reading begins to drift away from the actual salt level. If you rely only on the box for the salt level, and add salt to make the box read right, your actual salt level will usually end up at between 5,500 and 6,500 ppm. In other words, it takes a higher and higher salt level to maintain the same performance as the coating wears off.

I would suspect that your salt level is much higher than you think it is.