What makes the difference?

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woodyp

woodyp

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Apr 17, 2010
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Hayward Aquarite comes in 3 different.."capacities". The AQR3....9....and 15 rated for 15k gallons, 25k, and 40k respectively. What exactly makes these cells different in their capacity to generate more and more FC as they get larger. Is it the thickness of the titanium or the coating that is on those prongs, the amount of electricity that is passing through the SAME prongs.........or what?

Is there any factual data that says the lifespan of a larger size cell running on a pool at either less % output or for a shorter period of run time than say, a smaller sized cell to produce the same amount of FC would be any greater? Or is it all just theoretical?
 
There's also a T-5 cell. The difference is the number of titanium plates. The voltage sent to the plates is the same. The current is higher due to more plates. I'm not sure how many plates each have but I will check.

Edit- the number of plates is 13 or 7 depending on the manufacturer and model. Smaller models can use smaller plates or 7 plates or 7 smaller plates.end edit
 
Some good questions. Maybe there is some experience, but I think we PRESUME and perhaps rightfully so that if a cell runs less, it will live longer. Stands to reason, but I certainly have no proof or experience to back it up.
 
Yes, more plates in the cell increase chlorine gas output.

I don't have laboratory research to give you factual data. I do have a few decades of field experience. If you have a high output cell that runs less time or at a lower output, the cell lasts longer. That is my first hand experience.

Also, when the cell has light use, the need to remove calcium is reduced. Every manufacturer (except one that I know of) recommends soaking the cell plates in diluted acid. The acid soak also breaks down the ruthenium plating on the plates. That process is the major contributor to cell failure, so it would make sense that less acid washing would provide a longer life.

I will only install the SGS Breeze systems since the calcium removal doesn't require acid.
 
The life should be roughly proportional to the total surface area of the plates. I think that the t number is close to the number of plates. I think that the t-15 has 13 plates. There is also a t-15LL(long life) that has a thicker coating of ruthenium oxide on the plates.
 
If the voltage is held constant, the smaller units would have to use less surface area rather than less number of plates. The number plates has to be a constant with the voltage because the reaction requires a certain voltage between each pair of plates. Since the plates are in series, the voltage is split between each pair of plates. The nominal voltage of a T-15 cell is 26 volts and there are 13 plates or 12 pairs of plates (i.e. voltage gaps) so the voltage between plates is around 2.3v which if I remember Richard's post correctly, is above the reduction potential for the chloride ions.

I have never used the smaller cells so I don't know if the supply voltage changes but I don't think it does so the plates must be shorter but still the same number.

Also, the life of the cell (amp-hours) should only be dependent on the coating thickness (and pool chemistry). Smaller cells have smaller surface area but also smaller amps so amps/sq-in is the same between cell sizes. However, they have to be run longer to generate the same amount of CL so that does affect cell life.
 
I'm pretty sure that there are fewer plates in the smaller cells. I think that half of the plates get the positive charge and half get the negative charge. I think that the voltage between the plates is the full 24 volts dc. I think that the plates are wired in parallel.
 
No, I am pretty sure they are in series and I think I got that from multiple sources including these:

Economics of Saltwater Chlorine Generators
SWG - Amps Volts and bipolar cells
Designing new salt system - any suggestions?

Also, chloride has a reduction potential of 1.36 volts and the overvoltage is around 1 volt so 2.3v fits within the range. 24v is way more than you need and would have many side reactions. But if you are still in doubt, PM Richard.

Electrolytic Cells

[EDIT] - I just did a continuity test on my T-15 cell and one of the connector pins is connected to the center plate and the other pin is connect to both outer plates. The rest of the plates are passive. So the effective voltage between plates is actually 4.6v and not 2.3v.
 

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Ok. I will look in a smaller cell tomorrow and count the plates. I have looked before and I am almost certain that there were fewer plates. I know that the voltage is the same for all cells, only the current changes.

So, only three of the plates are connected to the power?

How do the other plates work?

Also, there are three pins. Which plate is connected to the center pin.

If both outer plates are connected to the same pin, is that in parallel or in series?
 
So, only three of the plates are connected to the power?
Click to expand...
Correct

How do the other plates work?
Click to expand...
These are passive and work like a resistor or capacitor. If you connect multiple identical resistor/capacitor in series, the voltage is divided between the resistor/capacitor equally so each resistor/capacitor will have 1/N of the total voltage. When the outer plates are energized, the voltage is divided equally between all the plates in between even though they are passive.

If both outer plates are connected to the same pin, is that in parallel or in series?
Click to expand...
Basically, you can consider it as two parallel sets of 6 series cells. So the voltage between any two adjacent plates is 26v / 6 = 4.3v.
 
JamesW said:
http://www.che.cemr.wvu.edu/publications/projects/prod_design/salt_chlorination.pdf

Here's a paper describing the voltage needed. Not sure if this helps for the cells in question. Based on the referenced paper, it looks like the plate spacing is important. Perhaps the plate spacing is adjusted to keep the voltage the same for all models.
Click to expand...
Yes, if you widen the space between the cells, the current drops and so will production. But for a fixed volume to increase the gap, you must remove plates and when you remove plates, the voltage between each pair of plates increase and given a fixed volume, the current will end up back where it was with more plates. For example, if you pulled every other plate, the voltage per pair would double so in equation 8 in the paper you posted, Vohm per plate would double and since S is doubled, IGap must remain the same. So the net effect is the same current and the same production. Also, I think efficiency drops with increasing gap size so that isn't good either.

I think the only way to reduce production for these cells where the total voltage is a constant is to reduce plate surface area A. That reduces IGap proportional with the same Vohm.
 
So, as best as I can summarize, it seems to work like this:

Depending on the polarity, the center plate and two outer plates are oppositely charged causing electrons to flow from either the center plate to the outer two plates or from the outer two plates to the center plate.

This causes the plates in between the center and outer plates to become positively charged anodes on one side and negatively charged cathodes on the other side. There are 12 anodes where chlorine gas is generated and 12 cathodes where hydrogen is generated in a 13 plate cell.

The amount of chlorine generated depends on the total anode surface area, either by plate number or plate size.

Example: If electrons are going from the center plate to the outer two plates, then both sides of the center plate would be cathodes where hydrogen gas is generated and the inside surface of the two outer plates would be anodes where chlorine gas was generated. The outside surface of the two outer plates would not be cathodes.
 
One can also have just two wires so two active plates with any number of passive plates in between. The voltage between plates is the total voltage between the active plates divided by the number of cells in between (number of passive plates plus one). This approach is an easy way to have electrochemical cells in series which lets one use a higher voltage so is a more efficient way of getting more electrochemistry at a lower current from the power supply (but an obviously larger total current in terms of one pair of equivalent plates with much larger area per plate).

As for degradation, the plates are rated in hours of operation because the degradation is related to current density times time. The current density is designed to be constant based on voltage and plate spacing so what varies is the % ontime. Degradation of the coatings and plate material occurs over time based on electrolysis, not when the system is off (that is, the degradation is active, not passive). This dissertation explores the effects of polarity reversal and other factors on the lifetime of coated titanium plate materials. The main failure modes are from coating (ruthenium and iridium) dissolution and from substrate (titanium) passivation (formation of oxides).
 

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