Question about SWG behavior

[basjke]

Hi all, I have a Zodiac Tri Large PH for about 5 years ago for which I kindly seek your advice.
I had the feeling that it didn't produce enough chlorine, but I can't be sure about that as I can't measure chlorine output, so I went through the trouble shooting guide.

The guide says that it should measure between 21V and 24 V at the cell output contacts, if outside these values it indicates a nominal amperage issue.

I measure about 23 V at the cell output contacts at start up, but this will gradually decrease to settle around 19 V after about 5 minutes, which according to the trouble shooting guide indicates a nominal amperage problem.

I then measure the current at the cell contacts and this reads 7.22 A and will gradually increase to +7.3 A, so this seems normal figures as the guide says the Tri Large should measure 7.2 A.

Some additional observations I did.
(1) When the voltage is at 19 V and I open the water supply, which feeds into the suction side of the pool pump and will actually dilute the salt content of the water going through the cell, the voltage will climb again to about 20 V.
(2) When I cut the mains power to the unit , and even disconnect the cell from the unit, I will still measure 2 V at the cell contacts which will very slowly decrease, but there will always remain a voltage.
So my question is if these observations are normal behavior or does this indicate a problem ? If the latter, is the problem with the power supply or the chlorinator cell?

Thanks in advance

I include a link to the repair manual so you can verify the figures.

http://www.vagnerpool.com/web/download/12408

Edit for some speeling mistakes.

 

[Jezza]

A couple of questions here

What are you using to test for chlorine levels in the pool? Assuming that your not adding any other source of chlorine does your pool look clear?

Does your chlorinator indicate any error messages or warning lights as described in the manual? Generally if all seems fine with your SWG (no error messages or warning lights) then it should be producing chlorine.

 

[basjke]

The purpose of this thread is to find out if the behavior of my chlorinator as I measure is normal, not about the sanity of my pool.

I indeed occasionally get a an "output fault" error message, at that point the cell will stop producing chlorine gas, but either the error will clear from itself or I will clear it by holding the select button for 4 seconds as explained in the repair manual.

So in short, is it normal that the voltage output to the cell fluctuates between 23 V at start up and just above 19 V during operation.and that the cell even when disconnected, always measures about 2 V DC.

 

[jblizzle]

I am not sure who on the board is going to have the answer to this very specific question.

I too wonder how you are testing and what makes you think the production has gone down and not that there is something consuming the FC.

 

[basjke]

I'm testing using Aquachek silver strips, but first of all strips are not 100% accurate, and I live in a tropical country so chlorine get consumed quickly by the sun.

I also try to keep CYA levels as low as possible, for obvious reasons, and again CYA levels are very difficult to measure accurately with strips.

The reason I ask is because here in Thailand the price of a Zodiac is 3 times the price it is in Australia, and not so easy to import due to a highly corrupt organization having offices at the port, so I want to be prepared when the system finally gives up.

I also not gonna import a power supply if the chlorinator cell is the one that causes these symptoms, or vice versa.

Someone with technical knowledge about SWG's, I think, should be able to answer my question.

The repair manual says that test voltage should be between 21 and 24 V, otherwise there is a nominal amperage issue. The same manual quotes that a Tri large should measure 7.2 A.

Well, my chlorinator measures 23 volt for the first few minutes, then drifts out of the recommended range, but there is not a amperage issue since it measure between 7.2 and 7.33 A at any time.

So is it normal that the voltage drifts to something like 19.3 V during operation or not? It also became clear that when the salt content of the water is lower, or maybe when the water is colder or lower in pH since my water supply comes from a bore hole and is low in pH and of course colder then the water in the pool, the output voltage rises.

All these factors are not described in the repair manual, but someone with the technical knowhow will probably know the answers.

So my question is pure technical.

 

[jblizzle]

Understood that your question is technical. But I'm more thinking you have a chemistry problem. I don't understand why you think a lower cya is better? That results in the chlorine being lost to the sun much more quickly.

 

[basjke]

I didn't say a lower CYA is better, but I consider it healthier, especially with young children using the pool.

I've also read that everything above 50 PPM doesn't make much sense, since the higher the CYA level the higher your chlorine level has to be to be effective, and again with test strips it's difficult to figure if you have 50 or 80 ppm CYA.

But that is just my opinion, and I think we're going off topic here.

Edit to add : I have no issues with my pool chemistry. My water is crystal clear, and the readings of my Aquachek silver test strips are fine.

The measurements of my SWG though indicate a problem, if I have to follow the repair manual to the letter, but I hope to get an answer if this is true or not and want to have the correct item at hand when and if it fails.

 

[JoyfulNoise]

Making voltage measurements across an electrochemical cell is not as easy as just touching the terminals with a voltmeter. The voltmeter itself can produce a potential drop and induce currents in the cell due to test lead metal differences and the internal electronics of the meter. Did you properly zero-out the voltmeter and leads before making the measurement. Analog meters are particularly bad because they can have low input impedance and can induce voltage errors as well.

The proper way to test a cell is to remove the power supply leads and then temporarily short the two leads of the cell to dissipate any stored charge (again ALL POWER SUPPLIES SHOULD BE TURNED OFF AND DISCONNECTED). Remove the shorting wiring. Then, you should earth-ground one lead and test the voltage on the other lead with respect to the same ground point. Swap the ground wire and do the same test on the other lead. The voltage difference should be zero or very close to zero depending on how good your meter is. There can be a small voltage relative to ground due to surface charge accumulation on the plate surface while sitting in an electrolyte. Also, If there are any on-board electronics between the leads and plates, then you can't accurately test the voltage drop as the electrical components will interfere with the voltmeter.

But a far simpler question to start with is this - did you pull the cell out and inspect the plates for calcium scale or damage? Scale isn't always visible and damage to the plate coatings isn't always obvious. Both coating damage and calcium scale will result in a lower plate voltage during operation.

 

[basjke]

Thanks for the explanation. I use a digital Elix meter and measure at the output contacts on the PCB, and yes after I short the two leads to the cell the voltage reduce to something like 0.3 volt.

I inspected the cell visually and don't notice any damages or calcium scale. The cell is also self cleaning and set at reverse cycle every 2.5 hours.

Also, is it so that with a damaged or scaled cell it will start at the recommended voltage then gradually over a period of about 5 minutes decrease to 19.3 V?

How do you explain the voltage increase to 20 V when I open the fresh water supply, and return to the previous measurement of 19.3 V, after the supply closure? Is it so that output voltage is adjusted to the salt content of the water?

I didn't mention this previously, but the voltage measured at the small cooling fan inside the unit is only slightly higher than the one on the cell output, and moves accordingly with the the voltage at the cell output.