Hayward SWCG incorrect Salt levels

[conphil]

Moved from here.

Well JamesW, now you've raised another question about which I was considering adding a new thread. (Since I'm new at this... let me know if new thread is warranted)

My new T-cell-940 does NOT report the correct salt level. And, yes, I understand that this "calculated" level is based on current, salt level, and temperature (plus one more thing... see below). This new cell reports 3400 to 3500 ppm. Actual salt level as measured by my pool service technician and confirmed by by own salt strip readings (2 different suppliers of strips) is 3100 to 3200 ppm. The variations in all sets of readings can be explained by minor changes in water caused by recent rains. (Temperatures are relatively constant.. heater always on). When the controller reports high (3500) , the strips read high (3200) and vice versa... lower values when the water becomes rain diluted. But there's always a difference of about 300 which I can't explain. I've taken MANY readings and believe the differences are significant.

The reason I started collecting salt strips from separate suppliers is because I was trying to digest the failure of my previous 5-year-old T-15 cell. Classically, that cell was reporting much lower salt levels than actual... while producing insufficient chlorine until we concluded it was at end-of-life.

It made me wonder if this ratio of reported / actual is the design intent. That is, does a new cell report a ratio higher than 100%; then as the cell ages, this ratio goes down eventually to near 75% and cell failure.

Does anybody else get higher values on new T-cells?

The rest of the story: My readings for current are about the same: new cell T-940 vs. old cell T-15 (7.5 to 7.9 amps), I keep my actual salt at 3100 to 3200, and temps are very similar. Clearly the old cell reported salt levels of 2600 to 2700 vs. the new cell at 3400 to 3500... so condition (age?) of salt cell affects what the monitor reports. (I think I read one blogger report this was a function of the amount of chlorine generated.... so maybe chlorine ions impact what the cell reports.)

I really appreciate all the feed-back... you guys are great!

 

[JamesW]

To get the performance percentage of the cell, divide the instant salinity reading by the actual salinity reading.

You need to be really sure about the actual salinity reading.

You need to use a K-1766 salt test kit or a calibrated meter.

K-1766 Taylor Salt Test

tftestkits.net

Salt tests are generally considered to be accurate +/- about 400 ppm.

So, that means that the readings can be up to about 800 ppm different and it’s considered to be within the limits of the test.

Typically, you want to see the tests within 400 ppm of each other, but I would consider up to 800 ppm acceptable.

Your readings are close enough, and the actual salinity is likely to be somewhere between the two values.

Just go by the box readout and don’t allow the amps to hit 8.0 because the unit shuts off at 8.0 amps*.

Periodically, check the performance percentage of the cell. It should stay constant for about 8,688 hours at 100%. When the cell begins to drop in performance, the cell is dying. When the performance percentage hits 75%, it’s time to consider replacing the cell.

T-Cell-15 (940) = 1.47 lbs/day = 40k gallons, 580 lbs. total trichlor equivalent lifetime = 533 lb chlorine gas lifetime or 362 days at 100% or 8,688 hours at 100%.

The 940 is the long life T-15 and you will get more total hours than the regular T-15.

*Note that a few software revisions use 10 amps, but most use 8.0 amps.

Hayward Aquarite SWG - Further Reading

www.troublefreepool.com

 

[conphil]

Thanks, James, for moving this to new thread.



I agree with you that most service folks suggest that variations from actual can exceed 400 or more. But that's not what I've monitored for about 4 years. My old T-cell-15 always reported salt levels within 100 ppm from "actual" salt strip readings (I have LOT's of data). Only when it started failing a few weeks ago did the monitor read much lower than actual.

The new T-cell-940 reports 300 high. Something is different!

Guess I don't need the salt level data if a difference of 800 is considered acceptable. 800 variation from 3200 typical salt level is a 25% error... Why would anybody accept a 25% error? That's unacceptable to me.

How many people depend on this reading to determine when and how much salt to add? A difference of 800 from actual is about 2.5 bags of salt for my pool..... way too easy to overshoot.

I will ONLY rely on external salinity measurements in future.

 

[JamesW]

You need to go by the box reading and not the independent reading. If the box hits 8.0 amps, it’s going to shut down.

The unit will work with a salinity reading as low as 2,400 ppm. At 2,700 ppm, the salinity will give a warning, but it will continue to work.

They could make the salinity test more accurate, but are you willing to pay twice as much for the system?

There’s no benefit in trying to make it more accurate than it is. It works just fine.

Get a K-1766 salt test kit to get a more reliable salinity test, but follow the box reading.