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Thread: SWG - Amps Volts and bipolar cells

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    mas985's Avatar
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    Valera,

    You wouldn't happen to have any curves that show chlorine production as a function of temperature and/or salinity?

    I am most curious about the chlorine production with salinity. My intuition tells me that it should be linear over a small range of acceptable salinity levels suggested by the manufacture (e.g 2800-3400 ppm). If this is the case, then cell life should not change much within this range. Lower salinity would have less amps but need to be run longer so amp-hours would remain about the same. This of course assumes that chlorine production is a linear relationship with current and salinity. Any thoughts.
    Mark
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    Salinity is not the issue for most modern SWG designs, as they use current/voltage control. When your salinity decreases the voltage applied to the cell increases to compensate. So within recommended salinity range chlorine production will be stable (and outside the range most units just turn off to prevent the damage to cell/power supply). For example our commercial units are capable of working with salinity from 3000ppm to 350 000 ppm (brine)

    What happens is that the control board senses the current, and adjusts voltage to keep the current the same, so consequently the chlorine production stays the same. So as long as your power supply can adjust the voltage to the necessary levels your chlorine production will stay the same.

    Current is not in direct relationship with chlorine, it depends on the design of a cell. For example our SMC cells require 5.3 amps to produce 30 gm/h.

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    mas985's Avatar
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    Unfortunately, my unit does not apply voltage compensation which is why I asked the question. The voltage is constant while current varies with salinity and temperature.
    Mark
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    Mark,
    Sorry, I do not have graphed data on those. But I must say that Temperature and Salinity have similar effect on SWG behavior but different effect on anode material operation and lifespan.
    In regards to your comment about salinity range and particular SWG, i need to know a lot more details about SWG mentioned to comment. Here is some general info:
    Most SWG use current control to maintain chlorine production at set level. So as salinity vary with in recommended range SWG will adjust operating voltage to compensate change in water conductivity ( salinity). Therefore current will remain the same so the chlorine output.
    So, lower salinity (as long as it is with in manufacturer specified range) will have no effect on chlorine production in SWG that have current control option.
    In regards to cell life it is more complicated. Let's say this, anode will last longer in solution with higher salt concentration, assuming the current remains the same. This is more to do with chemical processes that take place. You will be entering Holy Grail from here.

    Hope this helps
    =================

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    You guys are so much quicker in replying than me
    Mark, In case of fixed voltage and varying current you would be generally right.
    There will be some minor variations in life span of cell due to operation in different saline solutions, but it would only account for relatively small % of life span.
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    I might have a graph of current vs time which shows fluctuations of current during the day depending on temperature, but nothing about salinity.

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    Mark, one more think to consider:
    average non reverse anode material last say 15,000 hours at nominated load of 520Amp/SQM. If you half this load to 260Amp will will last more than twice as long. The actual life span of anode material can be requested from original manufacturer.
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    Thanks for the feedback. I think you have confirmed what I suspected that cell life is proportional to Amperage and time of operation (i.e. amp-hours).

    Also, a post from chemgeek some time ago showed the chemical reaction for a SWG and I think I remember that chlorine production rate was also directly proportional to amps. Therefore, for a fixed voltage system, chlorine production rate should be proportional to salinity as well.
    Mark
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    Quote Originally Posted by mas985
    Thanks for the feedback. I think you have confirmed what I suspected that cell life is proportional to Amperage and time of operation (i.e. amp-hours).

    Also, a post from chemgeek some time ago showed the chemical reaction for a SWG and I think I remember that chlorine production rate was also directly proportional to amps. Therefore, for a fixed voltage system, chlorine production rate should be proportional to salinity as well.
    It's not proportional to amps. It's proportional to Watts applied to the cell.

    As i said before we have SMC cells which consume 5.3 amps @ ~25V for 33 g/h , and then we have conventional cells which produce say 25g/h and need 25A @~7.5 V.

    It all depends on the way the cell is designed.

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    Quote Originally Posted by Strannik
    It's not proportional to amps. It's proportional to Watts applied to the cell.

    As i said before we have SMC cells which consume 5.3 amps @ ~25V for 33 g/h , and then we have conventional cells which produce say 25g/h and need 25A @~7.5 V.

    It all depends on the way the cell is designed.
    That makes no sense since it is the current that determines the number of electrons per second (that is the very definition of current) which determines the electrochemical output. Now, the current may be going to side reactions including the production of oxygen instead of chlorine, but it is the current (i.e. the electrons) that determine the quantity, not the voltage or watts (power).

    The voltage determines whether the reaction occurs at all since there is a minimum voltage needed for each type of reaction to start to occur (a base voltage based on thermodynamics plus an overvoltage corresponding to activation energy). I would think that higher voltage would make side reactions (i.e. production of oxygen) more likely though perhaps not by enough to be a problem. Higher voltage is also needed to produce higher current, all else (e.g. salinity, plate area, distance between plates) equal. If you design a cell with more plate area or where the plates are closer to each other, then the same voltage will result in higher current and higher output of product. So cell design does affect the voltage/current relationship, but the amount of output is solely dependent on the current alone. In SWG design, you can control the voltage and change the design of the cell and these both influence the current, but you do not "directly" control the current. The current is a result from these other factors that you do control (even a "current limiter" circuit works by essentially changing the voltage applied downstream).

    Richard
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    So essentially what you are saying is that our SMC cells produce 5.3 grams of chlorine per hour at 5.3 amps?

    Thousands of our customers beg to differ If that was the case their pools would go green in an instant

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    5.3 amps actually produces 7 grams per hour.

    5.3 amps is 5.3 coulombs/second. One Faraday is one mole of electrons and is about 96,485 coulombs. So 5.3 amps is 5.3/96485 = 5.5x10-5 moles of electrons per second. The chemical reaction that produces chlorine is:

    2Cl- --> Cl2(g) + 2e-

    and then the chlorine dissolves in water:

    Cl2(g) + H2O --> HOCl + H+ + Cl-

    so that the net (half) reaction is:

    Cl- + H2O --> HOCl + H+ + 2e-

    So it takes 2 electrons to produce one molecule of hypochlorous acid (HOCl). So the 5.3 amps produces 5.3/96485/2 = 2.75x10-5 moles of chlorine per second. The "grams of chlorine" is based on the weight of chlorine gas (all chlorine "ppm" measurements are based on that as well) which is 70.906 grams/mole so the 5.3 amps produces 2.75x10-5 * 70.906 = 1.95x10-3 grams per second.

    1.95x10-3 grams/sec * 3600 seconds/hour = 7.0 grams chlorine per hour

    If you were producing 33 grams chlorine per hour, that would be enough to raise the FC level by 0.87 ppm in 10,000 gallons every hour. Instead, the 7 grams per hour is equivalent to raising the FC level by 0.18 ppm in 10,000 gallons per hour.

    I'm not disputing that your cell may be outputting 33 grams per hour, but the output current to do that isn't 5.3 amps. Since 5.3 amps produces 7.0 grams of chlorine per hour then it takes 5.3 * 33 / 7 = 25 amps to produce 33 grams per hour.

    On your own website describing the SMC30T for example (see this link) it says it outputs 33 grams per hour with an input of 240 Volts and 300 Watts. I already calculated that it would take 25 amps to produce 33 grams chlorine per hour so that translates to 300/25 = 12.0 Volts if there were no losses (i.e. 100% efficiency). With some loss of efficiency, this could be 7.5 volts as you described. If I look at most of your models, it appears that they all operate at varying (by model) low output voltage since that makes the input power (watts) and voltage (240V) consistent with the gram/hour ratings. Of course, some variation is due to varying efficiencies and rounding of specifications. Specifically, we have the following all at 240V input. I used a conversion of 1 gram/hour requiring 0.76 amps and then derived a maximum output voltage assuming 100% efficiency of input to output power and that all the electrolysis is going towards the production of chlorine (i.e. no side reactions) at the anode. If there is less efficiency, then the voltages could be lower (with some of the "missing" input power going to heat losses and side reactions).

    Model ... Input Watts ... Output Chlorine Rate ... Required Output Current ... Maximum Output Voltage
    SMC20T, SMCA20, SMCE20 ... 190 Watts ... 22 grams/hour ... 16.7 Amps ... 11.4 Volts
    SMC30T, SMCA30, SMCE30 ... 300 Watts ... 33 grams/hour ... 25.1 Amps ... 12.0 Volts
    AMCINI ... 50 Watts ... 5 grams/hour ... 3.8 Amps ... 13.2 Volts
    AC15 ... 240 Watts ... 15 grams/hour ... 11.4 Amps ... 21.1 Volts
    AC20 ... 304 Watts ... 20 grams/hour ... 15.2 Amps ... 20.0 Volts
    AC25 ... 344 Watts ... 25 grams/hour ... 19.0 Amps ... 18.1 Volts
    AC35 ... 420 Watts ... 35 grams/hour ... 26.6 Amps ... 15.8 Volts
    AC50 ... 650 Watts ... 50 grams/hour ... 38.0 Amps ... 17.1 Volts
    AC100 ... 1400 Watts ... 100 grams/hour ... 76.0 Amps ... 18.4 Volts
    RPMINI ... 50 Watts ... 5 grams/hour ... 3.8 Amps ... 13.2 Volts
    RP15 ... 240 Watts ... 15 grams/hour ... 11.4 Amps ... 21.1 Volts
    RP20 ... 240 Watts ... 20 grams/hour ... 15.2 Amps ... 15.8 Volts
    RP25 ... 240 Watts ... 25 grams/hour ... 19.0 Amps ... 12.6 Volts
    RP36 ... 240 Watts ... 35 grams/hour ... 26.6 Amps ... 9.0 Volts
    RP50 ... 600 Watts ... 50 grams/hour ... 38.0 Amps ... 15.8 Volts
    RP64 ... 330 Watts ... 64 grams/hour ... 48.6 Amps ... 6.8 Volts
    RP92 ... 650 Watts ... 92 grams/hour ... 69.9 Amps ... 9.3 Volts

    Richard
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    Your calculations are correct, but they only apply to a conventional cell design.

    Our SMC cells use bi-polar design, so the calculations above do not apply.

    Our AC and RP range (with the exception of RP36, RP64 and RP92) use conventional cell design hence current = chlorine
    RP36, RP64 and RP92 use semi-bipolar design so you get 20A = 36 g/h, 35A=64g/h and 50A=92g/h

    Now SMC20 and SMC30 use bipolar cell, which gives you 3.4A = 22g/h and 5.3A=33g/h

    With bipolar design current doesn't matter so much.

    I'm not going to disclose technical details as they are commercial secret, however anyone is welcome to try one of our units and measure all the operating parameters themselves, in which case i can supply contact details of shops in US selling our equipment.

    Here is the brochure with more specs than on a website:
    http://www.autochlor.com.au/brochures/sm_complete.jpg

    Once again, if the operating parameters we are claiming weren't true we wouldn't be able to sell the amount of units we sold in the past 5 years.

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    Quote Originally Posted by chem geek
    I'm not disputing that your cell may be outputting 33 grams per hour, but the output current to do that isn't 5.3 amps. Since 5.3 amps produces 7.0 grams of chlorine per hour then it takes 5.3 * 33 / 7 = 25 amps to produce 33 grams per hour.

    Richard
    Here is the quick photo i made on a test bench.
    Obviously i cannot show how much chlorine it produces but take my word it is 33 grams/hour

    http://www.autochlor.com.au/images/33Grms5amps.JPG (~1.4mb)

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    Even in conventional cell design current does not equal chlorine numerically. 1 gram of chlorine per hour requires 0.76 amps of current.

    Your website page here says the following about the new bi-polar cell design:

    The new generation of bi-polar cells were developed to improve the ratio of chlorine generation to power consumption with a compact cell design. This effectively reduces the power consumption required to produce chlorine, making the system extremely efficient.

    There are many ways to improve efficiency and there is nothing inconsistent with having 190 Watts produce 22 grams/hour nor 300 Watts produce 33 grams/hour. The current and voltages I showed are perfectly reasonable to achieve that, especially for a compact cell design where the distance between the plates is closer and that is designed with good fluid flow to prevent buildup of products.

    Bipolar membranes are not new and are usually associated with producing caustic soda (sodium hydroxide) without producing chlorine from brine. Bipolar blades are also not new and just allow one to reverse the polarity so one can have a self-cleaning function (as opposed to monopolar blades that are optimized to always be an anode or always be a cathode). It is also possible that by bipolar you mean an anode on one side and a cathode on the other.

    All I was saying was that the total output current to produce 22 grams chlorine per hour had to be 16.7 Amps or that to produce 33 grams of chlorine per hour you had to have 25.1 Amps of current. You can, of course, split that into 2 banks in series which would be 25.1 Amps and a maximum of 6 Volts of voltage drop across each bank. This would be consistent with the photo you showed if the top number (25.4) were measuring current and the bottom number (5.2) were measuring voltage of ONE of two banks connected in series. This would imply 86% efficiency (25.1/25.4)*(5.2/6) which sounds about right. [EDIT] But wait, there is another explanation -- see below...

    None of what I said detracts from the point that a more efficient cell design will produce more chlorine for a given input power, but the actual amount of chlorine produced is based on the total output current flowing out from all plates. Improving efficiency means using a lower voltage which means more plate area or closer plates or more efficient removal of products (or higher salinity, but you don't control that).

    This patent defines bipolar cells in the context that I believe you talking about.

    So we have simply a difference in terminology since the current I am talking about is the effective current coming out of all plate area where electrolysis occurs while you are talking about the applied voltage and current to the cell assembly. The cell assembly itself, due to the cell design performs the equivalent of voltage to current transformation (so you can apply higher voltages at lower currents). As stated in the patent,

    In this disclosure, the term "bipolar electrode" means any electrode structure which acts as both anode and cathode during electrolysis and to which there are no direct electronic connections with the external power source.

    So I'm sorry for our misunderstanding. We were both right, but talking about two different aspects of current measurement. I was referring to total current coming out of the plates that generates chlorine while you were talking about the current coming out of your transformers into the cell assembly as a whole. It's kind of neat how the external higher voltage and lower current from the external source essentially induces a current flow in the bipolar plates that are in between. So essentially you transform your higher voltage at low current from the externally connected plates into lower voltage between the series of bipolar plates but with additional current going from one side of the plate to the other. It's interesting to note that the patent was filed in 1978 so the idea of bipolar cells isn't that new (though coatings and other advancements certainly are).

    [END-EDIT]

    Richard
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    Bumping this since I figured out our misunderstanding (see EDIT in above post). I'm sorry I didn't see that earlier -- I had to look up bipolar electrodes to figure it out (though I sort of guessed what it was in terms of a "series" of cells that I wrote in my above post). So the 33 gram per hour has 25.1 Amps coming out of ALL plates -- both the ones connected to the external power source and the bipolar plates not connected to any power source. The applied 25.4V with 5.2 amps current implies that about 19.9 amps is coming from the bipolar plates so if all plates are roughly the same size then that implies 4 bipolar plates, each having a current flow through them of around 5.0 amps. The voltage drop between each pair of plates (assuming equal spacing, area, etc.) is 25.4/5 = 5.1V.

    It's like having a series of electrochemical cells where the anode of one is connected to the cathode of another. You have to apply a higher voltage so that there is enough voltage between each pair of plates for the electrochemistry to occur (since the voltage drop between each cell is a fraction of the total) and the current flow from one end to the other is lower, but such current in a sense gets "reused" to go from oxidation to reduction to oxidation to reduction, etc., losing potential (voltage) at each step along the way. An alternative way of looking at this would be a series of batteries connected in series. The overall voltage externally seen is the sum of the individual voltages, but the maximum current capacity does not increase. However, with multiple batteries, that same current flow results in more chemical conversions (i.e. products) since there are more batteries.

    At least now this all makes sense so that the total current from all plates is 25.1 Amps (which is what I was saying) with a lower voltage drop between the plates of 5.1V while the current from the external power source is 5.2 amps with a voltage of 25.4V (which is what you were saying).

    Again, sorry for the misunderstanding. I get kind of riled up when I think the conservation of mass/energy law is being rewritten (which it wasn't).

    Richard
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    hehehe, gotta love geek's arguing!
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    Quote Originally Posted by EskimoPie
    hehehe, gotta love geek's arguing!
    Especially when it's mostly with myself. Gotta be frightening to look inside my head! These posts should probably be whisked off to the neurotic analysis section aka Advanced Chemistry.
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    mas985's Avatar
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    I for one am glad you took over this one.
    Mark
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