Does salt cell size matter?

[conmore]

Hi there

Before I contact the supplier I got my replacement cell from I thought it might be better to get an answer from experts. My original cell has 5 plates 200mm (8") long and including the clips is about 48mm wide, 30 amp and self cleaning (reverse polarity).
I decided to get a backup cell just in case it failed and I ordered a cell from a cell supplier with a good reputation from eBay. When I received the cell, first thing I noticed was the length of the plates which are 150mm long, not 200mm. I rang the supplier and he said it would be fine. So, assuming he knew what he was talking about it, I thought no more about it.

A couple of months ago I removed the original cell, cleaned it and stored it away and replaced it with the new cell and right away I noticed the output was about 20% or so lower than the original, so I turned up the chlorine production knob. Even with that full on high it only just gets into the green (Summer) setting by about 15%.
Yesterday I had my water tested at my pool shop and everything was fine except the chlorine level was low. They asked me how long I'm running the pump etc and told them it's been running for 8 hours a day for the past 8 weeks.
After I got home I removed the cell and installed the original longer cell and the meter went almost into 95% green zone so I turned it down so it sites between the two m's of summer, which is about 50%.
I paid top dollar for the new cell and want to know, if my theory of cell plate mass/length missing (50mm x 5 plates) is causing the lower production as per my meter?

Cheers

EDIT: Images of the original cell are in a post here: salt-cell-clips-t10528.html

 

[mas985]

Chlorine production is proportional to the cell size and current so a smaller cell should produce less chlorine. You should probably see it consuming less current as well. Because you will either have to run the cell longer or use more current to generate the same chlorine as before, this cell will probably last about 20% less than the original cell as well.

 

[Strannik]

Yes and no.

It's not as straight forward. If the anode material is exactly the same - yes it would mater. If anode material has different properties - not necessarily. Autochlor changed the size of their cells some time ago due to advances in anode manufacturing technology but it still produces the same amount of chlorine.

 

[conmore]

Yes and no.

It's not as straight forward. If the anode material is exactly the same - yes it would mater. If anode material has different properties - not necessarily. Autochlor changed the size of their cells some time ago due to advances in anode manufacturing technology but it still produces the same amount of chlorine.

Hi there

Then why would the meter on the chlorinator struggle to get into the green zone with the new smaller plated cell as opposed to the older larger plated cell going at least 75% of the way into the same zone with the current set the same if the material wasn't of the same type?

Cheers

 

[Strannik]

you'd need to ask the manufacturer of the cell
if they didn't use a material superior to that of original cell then they shouldn't have reduced the size
so either they sold you the wrong cell, or the manufacturer didn't know what they were doing

a lot of manufacturers who make generic cells usually don't know much about the properties of anode materials they use, and even less about what material was in original cell and what power supply actually drives it.

 

[mas985]

It's not as straight forward. If the anode material is exactly the same - yes it would mater. If anode material has different properties - not necessarily. Autochlor changed the size of their cells some time ago due to advances in anode manufacturing technology but it still produces the same amount of chlorine.

The only way a smaller cell could produce the same chlorine is that the smaller cell was run at a higher voltage or had the same area as the larger cell but in a different configuration. But I don't see how a cell of smaller surface area operating at the same voltage could possibly produce the same chlorine. It would violate the the physics of electrolysis.

The amount of chlorine produced by any electrolytic cell will be proportional to the amount of current running through the cell. The amount of current running through the cell is related to the voltage of the cell, plate size and conductivity of the water. The conductivity of the water is dependent upon the amount of salt and other dissolved solids in the water. As long as the plates are conductive and have little resistance themselves, then the composition of the plates should not affect the chlorine production at all. It may help with the life of the cell but not the chlorine production.

 

[New2Me]

Apparently the material has properties that can increase the amount of chlorine produced vs. oxygen, hydrogen etc...That is why chlorine production falls off over time, as the plating wears off. Or so I was told on another thread.

 

[mas985]

Apparently the material has properties that can increase the amount of chlorine produced vs. oxygen, hydrogen etc...That is why chlorine production falls off over time, as the plating wears off. Or so I was told on another thread.

Ok, I think I found the thread you were talking about here. That was comparing a cell with and without a coating. I would assume that all cells have this coating which helps favor the chlorine production over the oxygen production.

What I took issue with is that a cell plate area could be reduced by 20% and still have the same chlorine output.

 

[Strannik]

Apparently the material has properties that can increase the amount of chlorine produced vs. oxygen, hydrogen etc...That is why chlorine production falls off over time, as the plating wears off. Or so I was told on another thread.

But I believe that when the coating wears off, the cell plates are more vulnerable to the electrolytic reaction and the metal starts to be eaten away. It is the reduction in the cell plate area and the corrosion of the surface which reduces the electrolytic reaction which in turn reduces chlorine production.

I might believe that the coating helps ever so slightly with the chemical reaction so as to favor chlorine production over oxygen but I seriously doubt it is a 20-25% improvement to make up for the cell size difference.

nothing to do with metal being eaten away
you can make a cell out of bare titanium and it will never produce the same amount of chlorine as a normal cell, even when new.

as you said, the chlorine is directly proportional to current, and the way higher current is achieved is through the coating. without the coating you'd barely pull any current through the cell without increasing voltage. from memory, 2 titanium plates 65x100mm pull about 5 amps when bare, and about 50 with the same voltage when new.

so the coating which can allow more current through, will facilitate cell size reduction
now whether it's possible to achieve 25% improvement - depends how crappy was original coating and how good is the new one.

 

[mas985]

Yes and no.

It's not as straight forward. If the anode material is exactly the same - yes it would mater. If anode material has different properties - not necessarily. Autochlor changed the size of their cells some time ago due to advances in anode manufacturing technology but it still produces the same amount of chlorine.

But in this case, how much were they able to reduce the cell size and do you know if the plate area was actually reduced? One could always shorten a cell and widen it at the same time to achieve the same effective cell area.

Also, from what I can tell just by a Google search, Ruthenium Oxide use seems to be fairly common today for SWG cells so is there something new which is better than that?

 

[Strannik]

i'll lookup the figures, it was done couple of years ago but i think i still have it somewhere.
it wasn't widened. the gap between plates might have changed though.

i don't think there is anything else out there although i do know that some experiments have been done with other metals, just not sure on the outcome (it would be commercial secret anyway)

some anode materials use combination of ruthenium/irridium, but you cannot produce reverse polarity cells out of that material

here is some comparison of different manufacturers' materials we did a few years ago

as you can see some material is less active then the other

 

[Strannik]

found the figures for one particular cell

CELLRP20T which is a 20Amp reverse polarity 7 plate cell
Length of plates went from approx. 145mm to 110mm

 

[conmore]

you'd need to ask the manufacturer of the cell
if they didn't use a material superior to that of original cell then they shouldn't have reduced the size
so either they sold you the wrong cell, or the manufacturer didn't know what they were doing

a lot of manufacturers who make generic cells usually don't know much about the properties of anode materials they use, and even less about what material was in original cell and what power supply actually drives it.

Hi there

Well, by close investigation of the new cell compared to the original: the plate material looks exactly the same, but having said that I suppose it would be difficult to ascertain if the plate material was in fact superior to the original. And as I said in my original post: after installing the new cell I had to pump more voltage (I'm assuming that's what is occurring when I turn the chlorine production knob clockwise) almost all the way up to high to get the needle on the meter into the green zone. Bear in mind that I had the water tested and the salt level is OK and the report came back to either turn the chlorine production up or extend the hours of the chlorinator. It has always run for 8 hours a day during summer and been fine with the old cell.
Installing the old cell with the longer plates and I had to turn down the knob anti-clockwise (from 3.00 o'clock to 12.00 o'clock) and the needle on the meter is in the middle of the green zone.

All I wanted to know was I on the right track asking the cell supplier to rectify this?

Cheers

 

[Bama Rambler]

I think we got a little sidetracked between ourselves, but back to what you really want to know.

First thing, is there a model number or some identifying marks on the cells themselves? That would give you the first indication that the cells aren't the same model.

Second is, from your experience they definitely aren't the same cells. I'd definitely contact the supplier and outline your findings and ask that they replace it with the exact cell (at least size and coatings) you bought it to replace.

 

[Bama Rambler]

After doing a little searching, I found this. Looks like Omega is sold by the PoolStore in AU. The interesting thing is that they make several different cells that look like they all fit the same housing. They make a 15 amp cell that's ~160mm long and they also make a 20 amp & a 30 amp cell that's 200mm long. So it's beginning to look like you got the wrong cell.

 

[Strannik]

All I wanted to know was I on the right track asking the cell supplier to rectify this?
Cheers

you are on the right track
sorry for distracting you with all the techo stuff :-D

you wouldn't be able to see the difference in quality of coating with a bare eye (although you can sometimes see insect parts in chinese manufactured coatings under the microscope )
it's the differences in production technology that makes it or breaks it.

All companies might be using same components to produce the coating, but difference in proportions or other bits of technology can be fatal. Considering that not many companies in the world make it, there isn't much knowledge around on the processes and it's heavily guarded. So every company who wants to manufacture their own anodes has to pretty much start from scratch.

 

[mas985]

In this case, it sounds as though the loss in production can be accounted for by mainly the size reduction (-25%). Given that the setting was only increased by 20% to compensate, this may indicate that the new cell might even have a slightly better design.

Strannik,

A clarification on the chart you showed. Is "Activity" the same as chlorine production and the time of service the cell life?

If so, it looks like most of the cells have close to the same chlorine production except for #9. What is surprising is to see the large difference in cell life. Is the difference due primarily to the coating?

 

[Strannik]

activity is amps at fixed voltage and salt level
time - time of test

you are right, the difference in cell life is due to difference in coating technologies
Autochlor has spent about 10 years on extensive R&D to get to where they are now.

#4 is what Autochlor puts on big commercial machines which run 24/7 in aquaparks etc..

 

[mas985]

Sorry to be a pest but I am quite interested in this topic and I keep thinking of more questions.

First, were all the cells in the test of equal size and plate separation? I assume that was the point of the test but I wanted to make sure.

Although amps is a pretty good proxy for chlorine production, isn't some small percentage of the amps go into making a small amount of oxygen as well? One of things mentioned in this post was that the coating can affect the ratio of chlorine to oxygen production. Did the cells in this test have different coatings and if so, how do you know the relationship between amps and chlorine production without measuring chlorine directly?

 

[conmore]

Sorry to be a pest but I am quite interested in this topic and I keep thinking of more questions.

First, were all the cells in the test of equal size and plate separation? I assume that was the point of the test but I wanted to make sure.

Although amps is a pretty good proxy for chlorine production, isn't some small percentage of the amps go into making a small amount of oxygen as well? One of things mentioned in this post was that the coating can affect the ratio of chlorine to oxygen production. Did the cells in this test have different coatings and if so, how do you know the relationship between amps and chlorine production without measuring chlorine directly?

Hi there

Visually there was no apparent difference in the size of the plates and the separation between them. The noticeable difference was the length which was deficient by 50mm per plate x 5 plates which would equal having an extra plate, if my arithmetic serves me well. As far as plate material is concerned I have no idea if they were of the same type. My concern was how high I had to have the chlorinator and the lower output at that setting in comparison to the original cell.

I contacted the cell supplier with my concerns and have asked I send the cell back to them for testing, which I have done. I still believe it may be the right cell with plates not long enough, if that makes sense. This appears to be the right type of cell: http://cgi.ebay.com.au/ws/eBayISAPI.dll ... K:MEWAX:IT

Cheers
I will keep this forum posted with the outcome.