What is physically happening when a salt cell goes bad?

[TreeFiter]

I've been getting sent out quite a bit lately to acid wash salt cells only to find that they are being misdiagnosed. Usually it is a bad connection on one of the wires on the cell. I suspect that there have been a lot of salt cells that have been acid dipped over the years because of a bad diagnosis.

These frequent service calls got me thinking about how to tell that a salt cell needs to be acid washed, and when the cell's life is over and needs to be replaced.

My understanding is that they should only be acid washed if there is visible scale accumulating. Is this correct?

I have seen many situations where acid washing the cell will fix the problem even if there is no visible scale, but I suspect these were cases of bad wire connections. When the wires are removed to clean the cell, and put back on, the connections are fixed.

So what actually happens that causes a cell to die?

 

[bobodaclown]

I believe the chlorinator cell consists of parallel titanium plates coated with ruthenium and sometimes iridium and the coating wear out after time. I think most cells are rated for 8000-10000 hours of usage.

 

[mas985]

My understanding is that they should only be acid washed if there is visible scale accumulating. Is this correct?

Not necessarily - See Below

So what actually happens that causes a cell to die?

The coating on the plates wears off and exposes the base metal at which point the cell corrodes very quickly and the plate conductive surface area starts to shrink. This is why a failing cell tends to read lower salt because as the plate conductive surface get smaller, there is less current draw and the unit "thinks" that the salt level is lower when in fact it is the cell area that has reduced.

However, a dirty cell can behave in exactly the same manner and the only way to know for sure if it is a dirty cell vs a dying cell is to try and clean the cell. If after cleaning the cell, the salt read out is much lower than a drop kit reading, then you can be pretty certain it is a dying cell. You can also have the cell tested to make sure.

Just to add to the uncertainty, a leaking pool can also lead to lower salt levels but then the test kit should also read lower.

So to diagnose this issue, here is how I would approach the problem. If the PO complains about constantly dropping salt levels or low amps warning follow these steps:

- Test salt level with a drop test kit.

- If salt level reads ok, then clean the cell. If salt level reads low with a test kit, look for a leak (could also be due to splash out).

- If the unit salt level still reads low, have cell tested and replace if necessary.

 

[woodyp]

That^^^^^^^^^^^^^^my friends, needs to be a sticky or part of Pool School.

 

[TreeFiter]

Not necessarily - See Below

The coating on the plates wears off and exposes the base metal at which point the cell corrodes very quickly and the plate conductive surface area starts to shrink. This is why a failing cell tends to read lower salt because as the plate conductive surface get smaller, there is less current draw and the unit "thinks" that the salt level is lower when in fact it is the cell area that has reduced.

However, a dirty cell can behave in exactly the same manner and the only way to know for sure if it is a dirty cell vs a dying cell is to try and clean the cell. If after cleaning the cell, the salt read out is much lower than a drop kit reading, then you can be pretty certain it is a dying cell. You can also have the cell tested to make sure.

Just to add to the uncertainty, a leaking pool can also lead to lower salt levels but then the test kit should also read lower.

So to diagnose this issue, here is how I would approach the problem. If the PO complains about constantly dropping salt levels or low amps warning follow these steps:

- Test salt level with a drop test kit.

- If salt level reads ok, then clean the cell. If salt level reads low with a test kit, look for a leak (could also be due to splash out).

- If the unit salt level still reads low, have cell tested and replace if necessary.

This all makes sense, but I'm wondering, where in the process you would put checking the wiring and electrical connectors?

What would make a cell dirty besides visible scale?

For me, the first thing I check is how much salt is in the pool. Then I check electrical connections, as they are the easiest and least costly to repair. Then, I would acid dip the cell, and if that still didn't work, I would recommend replacing the cell.

The majority of the pools I deal with have one of two types of salt systems, and I'm noticing that one tends to be misdiagnosed far more often than the other, and I believe it is because of the type of electrical connections used.

 

[TreeFiter]

Not necessarily - See Below

The coating on the plates wears off and exposes the base metal at which point the cell corrodes very quickly and the plate conductive surface area starts to shrink. This is why a failing cell tends to read lower salt because as the plate conductive surface get smaller, there is less current draw and the unit "thinks" that the salt level is lower when in fact it is the cell area that has reduced.

If I understand this part correctly, the failure should be somewhat gradual, as the cell corrodes. I feel like I wouldn't expect to see everything is fine one week, and the next it is performing at 50%.

With EcoMatic salt systems they read 100 when operating properly, and are supposed to give some indication of the systems performance. For example if the salt level starts to drop, the system might start to read 95, and if it continues will work its way down from there. What I see when they are misdiagnosed is a reading that is much lower, for example, I had one that was reading 9 the other day. One week they are running fine, the next they are at 9. I can't imagine that a cell would fail so suddenly, or become dirty all at once. Am I correct in this assumption? The cell that was reading 9 turned out to be a poor connection. I pushed the connector on a little further and twisted it back and forth a few times and it went back to 100.

 

[mas985]

A failing cell will usually start working again if you add salt and the production rate drops over time so it is a slow process. Wiring issues are generally binary, either it works or doesn't plus wiring issues will usually generate a different type of alarm (no power, no flow, etc).

 

[JasonLion]

Cell failure can be fairly quick in many cases. The cell plate coatings have a thickness, which wears away slowly. Only when the coating is nearly gone do you start to see any change in performance. From there it isn't all that long until the coating is worn away completely and things start to really go down hill.

 

[TreeFiter]

A failing cell will usually start working again if you add salt and the production rate drops over time so it is a slow process. Wiring issues are generally binary, either it works or doesn't plus wiring issues will usually generate a different type of alarm (no power, no flow, etc).

I understand what you mean about wiring issues being binary, but in the systems I mentioned above, the terminals are exposed, and the connectors that attach to the terminals are also exposed brass. They develop a patina over time, which I think results in higher resistance. If they aren't on tight enough, or the patina is too thick, the resistance is high enough to give false readings. Often I find that one of the terminals is very hot due to the electrical resistance. Most of the time, these can be fixed by twisting the connection back and forth a little bit to scratch through the patina and sure up the connection.

In any case, I think you are confirming my suspicion that cells don't usually just all of a sudden fail. It would be more of a prolonged decrease in output that might show itself as a low salt or check cell warning on most systems, but doesn't get better after adjusting salinity or acid dipping cell.

- - - Updated - - -

Cell failure can be fairly quick in many cases. The cell plate coatings have a thickness, which wears away slowly. Only when the coating is nearly gone do you start to see any change in performance. From there it isn't all that long until the coating is worn away completely and things start to really go down hill.

Roughly how long would you expect it to take once the cell nears the end of its life? Is it something that can happen in a matter of a day or two, or is it more like a few weeks, or even months?

 

[JasonLion]

The duration of cell failure varies a bit, anywhere from a couple of days to a couple of months. About a month seems common. A couple of days would be quite unusual. But then you might not notice the initial signs, especially if the salt level started out fairly high or the percentage setting is particularly low. So it might appear to go quickly in some cases, even when it is happening at the same rate each time.

 

[mas985]

I think the reason a lot of cells appear to fail quickly is because somebody wasn't paying attention. The unit tells them to add salt and when they do, it starts working again so they tend to forget about it. Unfortunately for most SWG owners, by the time they do notice they have been adding a lot of salt over the last couple of months, the cell is pretty close to complete failure. But I think for someone who is on top of it and watching for a failing cell, they should have plenty of notice. I will let you know since I am now in my 9th year of the same cell and I expect it to fail soon.

 

[jmbradwell]

The time it takes a cell to wear out is also dependent upon your setting. Running your cell at 10% will last longer than running it at 100%.

 

[JesseWV]

This makes me wonder if they can be re-coated?

 

[JasonLion]

In principal, they could be recoated. However it isn't something you could do on your kitchen table, it requires quite a bit of specialized equipment. Also, since the coating is much more valuable than the cell plate and plastic housing, the economics favor making them new each time. I have seen a company that recycles cell housings, though I forget their name.

 

[JesseWV]

I guess we'll just have to wait for the guys who made FlexSeal (rubber in a can) to make ruthenium and iridium in a can!

- - - Updated - - -

In all seriousness though, I'm guessing you would need an electroplating setup with the necessary elements dissolved in acid?

 

[woodyp]

This makes me wonder if they can be re-coated?

Yep.....for about 500 bucks.............REPLACED!

 

[JasonLion]

I'm not sure if everyone does it this way, but at least some of the SWG cell plates are coated using vapor deposition, you put the plates in a vacuum chamber and then inject metal vapor.

 

[woodyp]

Metal vapor sounds interesting............

 

[JesseWV]

Interesting reading here: http://www.finishing.com/141/64.shtml


Hmm, I wonder if there's an alternative to ruthenium and/or iridium...

 

[ping]

Not necessarily - See Below

The coating on the plates wears off and exposes the base metal at which point the cell corrodes very quickly and the plate conductive surface area starts to shrink. This is why a failing cell tends to read lower salt because as the plate conductive surface get smaller, there is less current draw and the unit "thinks" that the salt level is lower when in fact it is the cell area that has reduced.

However, a dirty cell can behave in exactly the same manner and the only way to know for sure if it is a dirty cell vs a dying cell is to try and clean the cell. If after cleaning the cell, the salt read out is much lower than a drop kit reading, then you can be pretty certain it is a dying cell. You can also have the cell tested to make sure.

Just to add to the uncertainty, a leaking pool can also lead to lower salt levels but then the test kit should also read lower.

So to diagnose this issue, here is how I would approach the problem. If the PO complains about constantly dropping salt levels or low amps warning follow these steps:

- Test salt level with a drop test kit.

- If salt level reads ok, then clean the cell. If salt level reads low with a test kit, look for a leak (could also be due to splash out).

- If the unit salt level still reads low, have cell tested and replace if necessary.

Back to the original question, My understanding is that they should only be acid washed if there is visible scale accumulating. Is this correct? You answered this as not necessarily-see below. You mention a dirty cell, my question is why is acid used to clean a dirty cell. I would think a blast of water to clean a dirty cell and acid washing would only be used if there is calcium scaling.

My original cell never needed to be acid washed as there was only a slight amount of calcium build up that came right off with a chop stick and rinsed in water.