I had noticed that it seemed like my chlorine production was decreasing. It was summer and the outdoor temperature had been creeping up so I bumped up the duty cycle from 30% to 50%. I'm in coastal SoCal and I have a vinyl cover that is on most of the time so I get away with running only about 4 hrs per day. I checked and added some salt to bring it up to 3300 ppm, which is right in the middle of the target range (tested first with the onboard sensor, then with the $2-a-pop salt test strips. I checked the pH with an OTO test kit and added muriatic acid so that the pH was right at the low end of optimal. Note that I had gotten no error messages whatsoever from the system. I had proper flow rate indicated. The cell is oriented horizontally with the Salt/Temp/Flow sensor on the bottom. The cell was cell was cycling between normal and reversing and as nearly as I could tell, it was resting about in line with the 50% duty cycle. I had recently completely cleaned the DE filter and replaced all of the filter media. Other filter baskets were mostly clear of debris. Chlorine tests (both strips and liquid kit) at the outlet still were not showing any measurable chlorine production at an outlet. The new salt cell had been working flawlessly for about 15 months.
The chlorine levels were still decreasing so I decided to have a look at the plates on the cell itself. Before I took the cell out I confirmed I was getting 26.1-26.3 VDC at the connected contacts of the cell while the DC connector was lifted up slightly but still connected. Note only one side (center to one side) shows voltage potential at a time depending on whether it is in normal or reversing mode. After I removed the cell I could see a little bit of scale on the plates, but nothing that was even close to bridging or blocking flow.
So here is the strange part: I decided to see if I could measure any resistance between the plates of the cell. It should read extremely high resistance or open circuit, if I correctly understand the cell operation.
I set the multimeter to measure 20K ohms resistance and tested both ways - center to one side, center to the other side. The cell is disconnected and damp, but not immersed in water. Imagine my surprise when the meter read -8.1K ohms (!) That's right, the trusty, crusty old Craftsman digital multimeter actually read negative resistance. When I reversed the leads it read an open circuit so I assume that there is a diode in the meter circuit for resistance, (or in each side of the salt cell?) that allows current flow in one direction only. I wasn't able to definitively read any voltage potential across any of the unconnected cell contacts.
I assume that there was some sort of weak galvanic reaction within the cell that was causing a positive voltage change across the leads of the multimeter. I still haven't figured out what metal (or metal salt?) could have gotten in there and caused this.
So that was yesterday. I acid-washed the cell and forcefully spray-cleaned the cell and it seems to be producing chlorine again. Time will tell.
Does anyone have any idea how this could happen? Any ideas how to prevent it in the future?
Thanks,
Patch
The chlorine levels were still decreasing so I decided to have a look at the plates on the cell itself. Before I took the cell out I confirmed I was getting 26.1-26.3 VDC at the connected contacts of the cell while the DC connector was lifted up slightly but still connected. Note only one side (center to one side) shows voltage potential at a time depending on whether it is in normal or reversing mode. After I removed the cell I could see a little bit of scale on the plates, but nothing that was even close to bridging or blocking flow.
So here is the strange part: I decided to see if I could measure any resistance between the plates of the cell. It should read extremely high resistance or open circuit, if I correctly understand the cell operation.
I set the multimeter to measure 20K ohms resistance and tested both ways - center to one side, center to the other side. The cell is disconnected and damp, but not immersed in water. Imagine my surprise when the meter read -8.1K ohms (!) That's right, the trusty, crusty old Craftsman digital multimeter actually read negative resistance. When I reversed the leads it read an open circuit so I assume that there is a diode in the meter circuit for resistance, (or in each side of the salt cell?) that allows current flow in one direction only. I wasn't able to definitively read any voltage potential across any of the unconnected cell contacts.
I assume that there was some sort of weak galvanic reaction within the cell that was causing a positive voltage change across the leads of the multimeter. I still haven't figured out what metal (or metal salt?) could have gotten in there and caused this.
So that was yesterday. I acid-washed the cell and forcefully spray-cleaned the cell and it seems to be producing chlorine again. Time will tell.
Does anyone have any idea how this could happen? Any ideas how to prevent it in the future?
Thanks,
Patch