Salt PPM decreases with Pump at lower RPM

[Jaimslaw]

Strange. When I adjust my VS below 1500 RPM, my T-Cell 15 PPM reading drops down from 3200 to 2600 (triggering the low salt light). When I ramp the RPM back up above 1500, the PPM output returns to 3200 ppm and all is good.

Have verified pools salt levels and switched out my 6 yr old T-15 with a new one. Both act the same at the lower RPM.

Could this be a Flow Switch issue? (noting that I am not getting any low flow/no flow indicator). I would think that if its not signaling low or no flow, that the issue lies elsewhere.

I'm running the cell via my 10 year ago old AquaLogic PS-4. Could this be due to the main board's older software version (i.e., its an older version...not the latest version 2.60 or 2.65)? Or the infamous blown or bad resister on the back of the main board?

Would be nice to be able to run it at around 1100 rpm vice 1500 (a savings of around $4.00 oer month).

 

[thepoolman]

Never seen that happen and doesn't really make sense, but I wouldn't get too technical with it.

Try running your salt a little higher so it settles in at 2800-2900 when the RPM drops.

 

[JamesW]

Most likely it’s because, at lower flow rates, the chloride in the water is getting used up by becoming chlorine gas, reducing the amount of chloride for new production. Maintain sufficient flow to keep the reported salt level from dropping below actual.

 

[Jaimslaw]

Most likely it’s because, at lower flow rates, the chloride in the water is getting used up by becoming chlorine gas, reducing the amount of chloride for new production. Maintain sufficient flow to keep the reported salt level from dropping below actual.

This would make sense - but would that not make all T-cells 15 incapable of generating correctly at lower than ~1500 RPMs?

Also forgot to mention that these readings were with the cell level set at 15%. May mess around with those levels to see if anything different happens.

 

[thepoolman]

Also forgot to mention that these readings were with the cell level set at 15%. May mess around with those levels to see if anything different happens.

The 15% setting means that the cell is on for 15% of the three hour cycle that the salt system runs. The panel does not send more or less current to the cell according to this setting.

Run your salt higher and trick the system.

 

[JamesW]

This would make sense - but would that not make all T-cells 15 incapable of generating correctly at lower than ~1500 RPMs?

Also forgot to mention that these readings were with the cell level set at 15%. May mess around with those levels to see if anything different happens.

The RPMs are not the same as flow rate. Different systems will have different flow rates at the same RPM due to different resistance.

When the flow rate drops below a certain level, the production will be affected due to more gas in the cell and less water and chloride.

As noted, the percentage is not relevant.

Each system will have a minimum RPM requirement for optimum chlorine production. Try to find the lowest RPM where the salt level remains the same as at higher RPM.

 

[Jaimslaw]

The RPMs are not the same as flow rate. Different systems will have different flow rates at the same RPM due to different resistance.

When the flow rate drops below a certain level, the production will be affected due to more gas in the cell and less water and chloride.

As noted, the percentage is not relevant.

Each system will have a minimum RPM requirement for optimum chlorine production. Try to find the lowest RPM where the salt level remains the same as at higher RPM.

Been thinking about installing a flow meter, though I understand some inaccuracies do exist with different flow meters (and realizing of course that RPM and flow are inter related, ie higher RPM = higher flow rate). Not a critical component ...but hey, its a another pool gadget I can have fun installing.

I did a lot of RPM tweaking today and 1500 RPM was about as low as I could go before ppm moved down, and stayed at, 2600 (when moving rpm below 1500). What's more, I was able to bump it down to about 1350 rpm and all was fine (3200 ppm); but when it was off for any length of time and then turned back on, it would ramp down right away to 2600 ppm. For me to get it staying at 3200 ppm at the lower 1350 rpm setting, I woukd have to start off at 1500 rpm, and then back it off to 1350 rpm, where I could maintain 3200 ppm. I'm fairly certain, however, that if I let it run at that 1350 rpm for any length of time it would eventually creep down to that 2600 ppm level. So I'll stick with the 1500 rpm and be thankful that I am free of my old 2.0 hp running all the time at an energy hogging 3250 rpm.

Funny thing is, I bought a new $440 T-cell 15 thinking my 6 yr T-cell 15 was going bad on me; and that switching out my hi speed pump to a VS and setting it at 1100 rpm was just coincidental with the low salt readings I got at that lower rpm (and also was coincidental and coincided with a 3 month, 1:4 ratio acid cleaning). LOL. Oh well, will need to replace that old, still working cell in the near future - and prices will, I assume, only head north of what I paid.

 

[ping]

I suggest saving the old cell and use the new cell because the new cell has a warranty. The warranty on the new cell has already started and you might not need the new cell for a while, and if by chance when you install the new cell and it fails early, the warranty might be expired.

 

[Jaimslaw]

Will do. Thx.