Electrochlorinator Project

[Safrole Jay]

What plate spacing and voltage do electrochlorinators typically use? I went to the pool store and the floor model was just a fake demonstrator and the controller only listed input power. If anyone can give me a "for example" with certainty I would appreciate it.

Here's the project I'm working, since I can't be the only one that finds it interesting.

My pool is 55k gallons, so an electrochlorinator system is a bit pricey. Then again, so is the stabilized chlorine. I opted for a third route, and bought 4 double-sided anodes, 4"x14" each, of the 10,000 hr variety. That theoretically gives me either 224 or 448 sq inches of anode, depending on whether I run them as self cleaning (alternating polarity) or regularly, separated by stainless or titanium cathode plates.

Either way I use them, the plates are WAY beyond what's necessary, meaning I have a relatively wide window for plate spacing and voltage. I will be powering it with a light dimmer feeding 1 or 2 12v trannies, each of which can be center tapped for 6v. I'll rectify that to DC and will probably leave the waveform raw.

I'd like to err on the side of closer plate spacing, as opposed to pumping 24v in to get a decent output. But I could effect a redo, as the cell will sit inside a 6" PVC body with tons of space all around it and topped with a Y cleanout. If I botch the plate spacing too much I can remove the guts and rebuild. Of course I'd like to avoid all that...

I used patent 4085028 (which is tragically flawed) to derive a spreadsheet so I could play with voltage and spacing to get a ballpark amperage. (You're not supposed to push your anodes over 400 amps per square meter or the MMO coating starts to burn off at an increased rate.)

So (if anyone is still reading this) I would really appreciate a real-world figure for the plate spacing on one of the lower-voltage systems. I may also do a webpage with pics and explanations for the other mad scientists out there.

[Strannik]

From memory, the spacing on our transformer based models is around 5-7mm.

Voltage and current will depend on the size of the cell and the way you connect plates, if you browse the brochures on our site you will find some technical data.

You can also bump up your salt level to decrease the voltage.

Generally, the lower the voltage is - the longer your cell will last.

I'm afraid i can't get much more technical since i'm bound by non-disclosure agreement as I used to work in development of these buggers

Also i would stay away from using stainless steel as cathode, it will corrode very quickly. Use titanium plates, or even same plates as you use for anode.

If you get sick of playing with it - shoot me an e-mail and we'll see if i can give you the price to suit your budget. Btw we also supply anode material and titanium.

[chem geek]

The other key factor you want to know is that it is more efficient to use what is known as bipolar plates. These are basically just plates that are not connected to the external power supply and are placed in between the two plates that are connected to the power supply. In effect, you create the equivalent of a series of cells with the bipolar plates acting as an anode on one side and a cathode on the other. You drive such a system at a higher voltage, but the result is that the current is low through your power supply and the amount of chlorine generated is higher due to the greater plate area. The voltage between each pair of plates is low -- but because these are in series, the voltage applied by the power supply is higher.

It's a clever design and most SWG manufacturers now use it. Obviously it will require some clever mounting on your part to keep all these plates spaced evenly apart from each other and limiting the amount of electrolyte (ion) flow between each of these "cells" (areas between adjacent plates). Many systems use two active plates externally connected and four bipolar plates in between them for a total of 6 plates which creates essentially 5 cells serially connected. Typical external voltages in these systems are around 25V so that's 5 Volts per cell and typical current is around 5 Amps through each cell and for the system so that the power is 125 Watts, though obviously these details can vary depending on the size of the cell -- yours will likely be larger than this so will need more power from using larger plates or more bipolar plates (one way or the other you need more area -- assuming you can't make the plates get any closer together). Basically, the bipolar system gives you a larger plate area in a compact volume, a low voltage in each cell while having a higher voltage that is easier to regulate in the power supply, and a lower system current that has lower resistive losses. It also helps make the electrochemistry more efficient by not building up products as much compared to a much longer cell with fewer plates.

One very important thing not to forget is a circuit that switches polarity every so often since that prevents scale from building up. This is usually done on the order of some number of hours because switching polarity too often lowers the life of the plates while waiting too long can have too much buildup of scale and the resulting lower efficiency (and wear).

Richard

[Strannik]

If you decide to go for bipolar design, make sure that the loose plates are properly aligned and don't have the opportunity to slide from flow of water through them. If one of the bipolar plates slides out, the electrones instead of going from surface of one plate to surface of another will go from surface of one plate to the edge of another. Now since the edge of the plate has much smaller surface, and usually is not coated with ruthenium, it will be eaten within few months.

By the way, chem geek, that's the true reason behind corrosion of titanium electrodes in cells, to which TPG was referring in his blog.

[Safrole Jay]

Thanks. I'm not going to try bipolar plates, though my anodes are indeed double-sided. I didn't like the idea of higher voltages and the tendency of current to flow around the intermediary plates rather than through them and do work. I should think little "leaks" there would indeed (especially at those higher voltages) tend to corrode the substrate.

Now I'm parroting what I've read, but I thought exposed titanium substrate oxidized into titanium dioxide (the white base in most paints) which has an insulating effect. In this way the areas where the catalyst coating wears out become dead but it is not "eaten" electrolytically, and the blade continues to function. But of course the reduced catalyst area bears the same amperage, so it's a snowballing problem - but in the case of a scratch or chip you don't get a massive failure.

Please straighten me out there if I'm wrong, because I did not plan to seal the factory sheared edges of my plates, but could do so if necessary. Maybe epoxy or epoxy paint? Polysulfide or urethane?

The arrangement I've chosen is to have the four blades in alternating polarity, with two grounded plates on either end. I ordered a timer relay from Mouser, DPDT because I'm too lazy to horse around learning about 555 circuits. That will let me switch the polarity every hour and a half or so. One grounded end plate will always be vestigial.

I didn't have enough titanium to use that for ground plates, so I went to Ace hardware today and bought two pieces of 6x12 stainless, just a couple inches short but hey...

Again I'm just repeating what I've read, but I thought grounded stainless could could act as a cathode and not dissolve? I appreciate real-world advice.

Oh I opted for a theoretical 12v across .5 inch (12mm) which is a big gap, but I calculate with 224 sq inches of active anode on any given polarity cycle, it would still pull 56 amps which is the max current per area. I'm no mathemagician, but that sounds WAY high anyway. And I know I'll drop some voltage across the rectifier, but even so I think the dimmer will be next to zero almost all the time. I may even go to the center taps (6v).

I plan to run this monster cell very lightly to make it last as long as possible. Yes I am very much considering higher salt concentrations to that same end. Also the flow across the cell will not be fast at all, as it will be in parallel with the return.

[Strannik]

Now I'm parroting what I've read, but I thought exposed titanium substrate oxidized into titanium dioxide (the white base in most paints) which has an insulating effect. In this way the areas where the catalyst coating wears out become dead but it is not "eaten" electrolytically, and the blade continues to function. But of course the reduced catalyst area bears the same amperage, so it's a snowballing problem - but in the case of a scratch or chip you don't get a massive failure.

Please straighten me out there if I'm wrong, because I did not plan to seal the factory sheared edges of my plates, but could do so if necessary. Maybe epoxy or epoxy paint? Polysulfide or urethane?

It doesn't insulate it good enough If you assemble a cell out of 2 bare titanium plates they will draw around 5 Amp with the applied voltage of 12-13V. Normal anode plates will draw around 30-50 Amps, depending on coating. Generally we don't seal the edges. It only becomes a problem when one of the plates moves out. Currents can eat titanium within 2-3 months.

Bipolar design is particularly prone to this problem since not all of the plates are welded together. If you are not planning on using bipolar design I wouldn't worry about sealing the edges. Just make sure that all your plates are of the same size and don't protrude too much. 1 mm align difference is ok.

The arrangement I've chosen is to have the four blades in alternating polarity, with two grounded plates on either end. I ordered a timer relay from Mouser, DPDT because I'm too lazy to horse around learning about 555 circuits. That will let me switch the polarity every hour and a half or so. One grounded end plate will always be vestigial.

Just make sure that you have a position where none of the plates are connected, otherwise there is a possibility of short circuit when you switch polarity.

I didn't have enough titanium to use that for ground plates, so I went to Ace hardware today and bought two pieces of 6x12 stainless, just a couple inches short but hey...

Again I'm just repeating what I've read, but I thought grounded stainless could could act as a cathode and not dissolve? I appreciate real-world advice.

Put it this way, if the stainless steel was good enough - manufacturers would use it instead of titanium to save costs I think you'll find that it will corrode away in about 3 months if not earlier.

Oh I opted for a theoretical 12v across .5 inch (12mm) which is a big gap, but I calculate with 224 sq inches of active anode on any given polarity cycle, it would still pull 56 amps which is the max current per area.

I would seriously consider closing the gap and running at lower voltage. High voltage is asking for trouble.

[Safrole Jay]

You make a great point: if it could be done more cheaply - they would! Also I will take your advice and move to .25 inch spacing. I am going to go ahead and seal the edges since I'll already have epoxy mixed up to coat the four points where the juice goes into the plates.

I am trying to insert a scale layout below. The stack of six plates is sandwiched by six stainless bolts, the shanks of which are wrapped in heat shrink tube. The end plates are grounded through these bolts to the grounded 3/4 tube steel chassis. That chassis hangs from rubber expanding nuts (well nuts) from the PVC cleanout cap. In this way when I need to service the cell, I pull the connections to the cap, unscrew it, and the whole 36" long assembly slides out as a unit. (So I can replace my corroded steel end plates with titanium, heh heh)

The bottom of the two main spars will have a 6" stainless threaded rod through them to maintain distance to the sidewall, to stop any oscillation/fluttering. They are not stainless but I figure they're farther from the anodes than the cathodic plates they secure, so painting or a bit of epoxy goop will suffice.

Now is the part where I drill holes in my $300 of plates. **wince**

[Strannik]

Looks nice. But do yourself a favor and replace everything you can with titanium

Those bolts will rust in no time, along with stainless tube. Or cover everything in epoxy:)

Also don't know about heatshrink, i would go for epoxy, or nylon tube slid over the shank.

Here is a picture of one of our commercial cells, maybe it will give you some ideas:

[Strannik]

Another thought - don't forget the flow switch, or your system might fly away in pieces

[Safrole Jay]

Strannik check your PM.

I was going to mount it on it's side and wire it in parallel with the pump and not worry about hydrogen evolution. I know that sounds capricious at face value, but my evolution should be much less than normal because of the underloading of the anodes. So the pump has to die (or lose prime) long enough for HHO to build up in the return line, then flow out and find a source of ignition. It's just hard to worry that many steps away. But maybe another idea.

Instead of a "flow" switch, maybe I could use a regular well pump pressure switch, which seems more easily incorporated into a homebuilt project. A cheap SquareD pressure switch cranked WAY down right off the pump head. I know it's opposite of what's needed: closing the circuit at low pressure instead of high. But if it's not double throw, then adding a NC relay would make it work.

Using that setup, you'd have to add on another rare eventuality before you could get a disaster: "pressure at the pump head doesn't equal flow through the cell".

[Strannik]

It's not so much the hydrogen, that should be a concern. If your flow stops, the cell will boil the water inside the housing in a matter of minutes, and uPVC only holds 65-70 degrees, then it starts to soften and bend.

[Safrole Jay]

Okay I have the thing almost finished. I took your advice and changed the end plates to titanium. I coated everthing steel with envirotex epoxy, but I'll inspect periodically for any cancerous developments.

I used an RV transfer switch to handle the duty of the alternating polarity. They have bars going from one contactor to the other to preclude simultaneous operation. Plus they each have smaller NC contacts, through which you route the power to energize the OTHER contactor. In that way the neighboring coil can't energize until well after the first one is open.

It ended up being a rats nest of wires, but it runs fine. I'll hopefully get time to replumb the returns this weekend and find out if it can perform under load. I'm a bit leery of a "50 Amp" relay with such spindly little legs on it. I heat sinked and thermal pasted it pretty well and have directed the air flow over it.

The one thing I forgot is an ammeter. Jenius. Anway I'll probably add that in, though I don't know where. I almost went to a second box as it is.

Here are some pics. The thing is outrageously sturdy.

before epoxy goop

epoxy-cicle

rats nest

cap wiring

one minute urethane - I love this stuff

the finished "look"

The quick and dirty schematic, minus the dimmer switch and main power switch

[Strannik]

Looks good.

Also i would include a circuit breaker or a fuse on the secondary side, to make sure you don't burn your trannies accidentally by putting too much salt in. And those wires that go to the cell don't look like they will handle 30 Amps (which I assume will be max output?).

Fire her up and let us know how it goes

With regards to Ammeter - you will need to put it on one of the leads going to the cell.

[Safrole Jay]

The skinnier 14 gauge conductors are only inside the cell, and work in parallel. I used heavier 12 gauge from the box to the cap.

I wasn't thinking right about the polarity - that I didn't need to run four separate conductors to the cap but only two, since the polarity switches INSIDE THE BOX.

You're right I planned - in a hazy, beer-fogged sort of way, on 30A max duty. My "fuse" as it were, is a solder connection to the positive leg of the rectifier. I figure that's the hottest spot in the whole system, so I'll plan for failure there first. I do have some high amp fuses from the dozen or so microwaves I've salvaged for parts.

To be honest this has been such a MOUNTAIN of work that I'm chicken to push it much at all.

[Strannik]

I would put a proper fuse and don't rely on solder connection.

It can handle 30A with no problem.

[Safrole Jay]

Do the plates in a cell acquire a charge that persists after you cut the power? It's the weirdest thing - I run it for a few minutes at 4 volts or less, until I feel the rectifier warm up, then I cut the power. But the test leads are clipped on, and they continue to read a voltage that diminishes over the course of time. (maybe 20 minutes, I never watch to completion) If I short the leads it doesn't spark or anything; it has no amperage whatsoever, but it starts at about 1.75 volts and drops linearly with time.

I'm gonna guess that the 1.75 volt capacity is a function of plate area. Does this indicate that immediately reversing polarity to the plates is hard on them? like shifting your car into reverse while in forward motion? I could just scrap the reversing polarity idea and plan on cleaning the plates every month or so.

I burned up my first rectifier. I don't see how you could ever push 50A through that thing unless you had some form of water cooling. It was my fault in the end because the bolt holding it against the heat sink had become loose. But even while tight it was so hot the heat sink would burn your fingers.

That rectifier was rated to hold back 1000v. Well I went to Radio Shack and got a pair of 25A bridge rectifiers, rated at only 50v. Each one is identical to the physical package of the 50A from mouser. That tells me there's internally more parallel diodes per package. Anyway it runs a lot cooler, and I added a micro DC fan right on top the heat sink.

My FC is about 5ppm right now since last night I gave up and dumped 2 gallons of liquid chlorinator in there. So after it drops I can check performance. In my initial runs it was hard to test the return water (from one of 3 returns) for presence of FC. I think it will take 12 hours from a point nero zero FC to be able to assess functionality.

[Strannik]

Do the plates in a cell acquire a charge that persists after you cut the power? It's the weirdest thing - I run it for a few minutes at 4 volts or less, until I feel the rectifier warm up, then I cut the power. But the test leads are clipped on, and they continue to read a voltage that diminishes over the course of time. (maybe 20 minutes, I never watch to completion) If I short the leads it doesn't spark or anything; it has no amperage whatsoever, but it starts at about 1.75 volts and drops linearly with time.

I'm gonna guess that the 1.75 volt capacity is a function of plate area. Does this indicate that immediately reversing polarity to the plates is hard on them? like shifting your car into reverse while in forward motion? I could just scrap the reversing polarity idea and plan on cleaning the plates every month or so.

Yep, its like a battery. It's best to short the plates before switching polarity to discharge them, but it's not essential.

[Safrole Jay]

A little advice if you can spare it

Something is not working well. (big surprise) I can crank it up until it's hitting around 6 volts, then the 25A fuse blows. So that's about 150 Watts, around half of the power I want. The chlorine production is either negligible or non-existent.

I have 3200ppm TDS after adding salt to a the starting water of 300ppm TDS. I thought that would be sufficient but should I add more? I'm going to bump it up to about 4000 and see anyway.

Everything in the power supply is warm. I don't have an ammeter, but it seems curious that the cell seems too "shorted out" to run the volts any higher. Is that normal, that you never get close to the no-load voltage?

I don't know where that 150 Watts is going, but I'll put an easy 30 in the power supply internals. The rectifiers are quite hot, even with direct cooling on their heatsink.

Inside the cell, all positive current is carried by 2 solid core AWG14 conductors. Are those too thin? I think that equates to 1.626mm. Maybe all I'm doing is heating up water in the cell with my skinny wires. ?? You mentioned this before but I'm loathe to crack the thing open unless you think it's an obvious shortcoming.

My next step is to disassemble the cell, put it INSIDE THE POOL and watch the operation up close and personal. In that way I could feel if those wires are warming up and dissipating power.

I have an electrical engineer friend who worked at a place designing switch mode power supplies for RVs. (I live in Elkhart, Indiana) They have one-off prototypes they built that are just sitting in their office, so he can get me a 50 or even 100A supply for nothing but a thank-you. But before I chase him down I'm thinking something could be wrong with my cell or salt concentration or something, as even my puny homebuilt supply should effect measurable results. Any red flags you could point out are much appreciated.

[Strannik]

Well 1.62 mm seems to be rather small. On our 25 A models we normally use a cable with a core diameter of about 5 mm, so yeah, i guess you are mainly heating water.

[Safrole Jay]

The wire was indeed too thin. Once a connection burned completely up it was really easy to get a full 12 volts!

And it became obvious that my ground plates are going to scale up like crazy, since they never switch polarity.

That's going to mean the 3 interior cells conduct most of the amperage while the two outer only work a couple days after cleaning.

This made me think. Since you have to periodically add muriatic to the system anyway, how crazy would it be to pour in a quart or so at one of the skimmers? Would this brief stream of 1/10th (?) muriatic do anything towards cleaning the cell? If this idea is viable, I'm guessing I should bypass the sand filter, as that would mix the stream with so much water as to be useless.

On a positive, I am definitely making chlorine now. Even the pathetically weak cell was making some chlorine, as evidenced by the oxidation on the electrically-isolated steel bars. You can see the lines of the two sheets of stiff poly liner between the bar and the titanium plate. Maybe this simply acted as a dielectric and "radiated" charge through the bar, dunno. 3-4 volts just isn't much to insulate and the plates are always at ground.

The new version of the cell dispenses with steel. I cut an acrylic sheet and pinned the plates right to it with nylon screws and heavy conductors. I also sealed with Life Caulk from the marina. It's polysulfide, which is evidently God's gift to the sealant world. Very rubbery, very secure bond.

This cell really takes the amps, revealing weakness in the power supply, again. I'm getting a free 60A converter, mosfet I believe, in about a week. I have to figure out how to effect current limiting, short of putting about 4 microwave oven transformers between it and the mains, heh heh.

Strannik I have to thank you so much for your advice. But I also have to ask about a part of it in light of what I'm seeing. My puny power supply is hitting its amperage limit WAY before max voltage. I blow the 30A fuse at about 4.5 volts, even lower if I give it some time to get hot. If my plate spacing were wider, I would be able to attain a higher voltage at that amperage. Isn't chlorine output all about the Watts? If I double my plate spacing to one half inch, 12.5mm, maybe I could pump the full 250W through the cell. Is that my system bottleneck?

Running 3.2 volts at an (estimated) 20 amps is only 64 Watts. Shoot, let's say 30 amps and make it 96 Watts. Obviously this isn't going to feed my pool adequately. Oh I have to eat some crow about my volume. The previous owner told me 55k gallons. Wrong. My backward calculations from adding salt and measuring TDS put it about 35,000 gallons. Anyway this "little" 60-90 Watt cell can can gain about 1ppm chlorine overnight, and at a low overall level can actually maintain during the day.

[Strannik]

This made me think. Since you have to periodically add muriatic to the system anyway, how crazy would it be to pour in a quart or so at one of the skimmers? Would this brief stream of 1/10th (?) muriatic do anything towards cleaning the cell? If this idea is viable, I'm guessing I should bypass the sand filter, as that would mix the stream with so much water as to be useless.

You also need to make sure there is nothing else on the way, like heater etc. Personally, i would clean the cell, or make a system which can isolate the cell so you can pour acid directly in cell chamber. I think that if you put acid in skimmer firstly it will be too dilluted by the time it reaches the cell, and secondly it will be gone very quickly, so it won't do much.

Strannik I have to thank you so much for your advice. But I also have to ask about a part of it in light of what I'm seeing. My puny power supply is hitting its amperage limit WAY before max voltage. I blow the 30A fuse at about 4.5 volts, even lower if I give it some time to get hot. If my plate spacing were wider, I would be able to attain a higher voltage at that amperage. Isn't chlorine output all about the Watts? If I double my plate spacing to one half inch, 12.5mm, maybe I could pump the full 250W through the cell. Is that my system bottleneck?

It's not the wattage that matters, it's the Amps. Ohm's law is U(voltage)=I(current)*R(resistance). when you change plate spacing (or salt level, or water temperature) you effectively change R, so to achieve the same I you need to change U. Chlorine output is roughly dependant on current applied to cell plates. So if you increase plate spacing you will just make your cell inefficient, but it won't make more chlorine. If you want more chlorine you need to increase your power supply capacity.

Hope that helps

[Safrole Jay]

Well that's disappointing, but it jives with Farraday's law. The plates are recommended to run at less than 400 amps per square meter. That can't be enough. One square meter is 1550 square inches. Figuring (conservatively) that my 3 interior cells must handle all the amperage means I have 3 anodes of 3x14 working at any one time. That's 126 sq inches. 126/1550*400=32.5 Amps maximum. That loading advice seems way too conservative.

I see on watermaid's site (http://www.watermaid.ca/4.htm) that they're selling a replacement cell they say will handle pools up to 150k liters (39k gallons) that has 310 sq cm, 48 square inches. They say it has "30 Amp cables". If they're putting 30A through 48 Sq inches, that's 968 Amps per meter, over double. Even 20A is still 645A/m2.

You and Mr. Farraday say it's basically amps turning into chlorine. This means that pool size dictates amperage. 30A should support my pool, so I must not really be delivering 20A or whatever I think I am. Maybe my new power supply should be the ticket.

Hey I have another idea to run past you -

Generally the cathodes scale up, but the anodes don't, right? If I were to use titanium plates for cathodes between every double-sided anode and on the ends, then maybe I could still reverse polarity in a "self-cleaning" cycle. The hope is that the scale would break loose, but do you think oxide would form on the plates, decreasing their effectiveness later?

[Strannik]

They are using mesh, it's different. I'm not sure how to calculate correctly the current density for it.

Now in your case, you need to multiply area by 2, because you have 2 sides of each plate which are working (assuming you have cathode on each side of anode plate).

As far as self cleaning goes, imho it won't work that way because there won't be enough ion exchange to get the scale off.

[Strannik]

So how is it going so far?

[Safrole Jay]

The project and I went into hibernation over the winter. Just before that I got a free switchmode power supply from a friend who works at an RV supplier. His ironic generosity got me an 80A unit instead of 40 or 60, So it was really cooking my cell. I don't have the know-how to throttle back a supply like this, so I'm planning on simply running less salt.

If I can get the performance of the system up to the point where a four hour duty cycle will sustain the pool, then running it all day might suffice for a shock. But I don't have to shock very often so I may just stick with hypochlorite for that. I also have a second, smaller sand filter full of that Zeolite stuff, which is supposed to filter chloramines. If it really works as advertised then maybe I could divert over to that filter periodically for "shock", a cleaning of chloramines. Then it could be very long indeed between true shocks. The second filter is already plumbed in as I was planning on running them in parallel.