Keep Your Swamp Cooler From Becoming a Swamp Thing




About: I like to tinker and experiment with electronics, robotics, programming, and photography. Along with my latest interest in Steampunk.

Swamp coolers collect and breed all kinds of bacteria and mold in the water. As the cooler operates, these organisms can travel into your home and cause a variety of health problems. Chemicals can be added to the water to kill bacteria, mold and algae, but can be difficult to maintain.

It's be a proven fact that Bacteria, Molds and Algae can be killed by introducing copper and zinc ions into the water. Silver works very well to, but may be difficult for the home owner to construct a proper electrode.

All that is needed is to connect a suitable electrode of these metals to a DC power supply. The following shows how I made a simple ion generator.

For the emitting electrode I used a brass pipe found in a hardware store. Most brass material is composed of 60 % copper and 40% zinc.

For the DC power supply, only a milliamp (1/1000 th of an amp) is required. I used a 2 watt 62K resistor in series with an 1N4005 diode and connected it to a line cord for plugging into the 120 AC outlet that powers the swamp cooler pump. Heat shrink tubing covers the assembly. The diode forms a half wave rectifier and the resistor limits the short circuit current to about a milliamp. Ions are generated on the positive half of the line frequency and travel off the electrode as bursts of ions at 60 hertz.

The resistor value determines how many ions are generated. It operates like the principle of electroplating, but in reverse. We are "unplating" the zinc and copper from the brass pipe.

Step 1: Build the DC Power Supply

You will need a 1N4005 diode and a 62k ohm 2 watt resistor to make a pulsing DC power supply

Step 2: Mount Diode and Resistor

Mount the diode and resistor on a piece of perf board. The band (cathode) of the diode should be toward the left. The direction sets the polarity.

Step 3: Bend the Leads

Be sure to observe polarity of diode. The line cord is soldered at the resistor end and the electrode is attached at the diode end.

Step 4: Solder Joint in Middle

Don't forget to solder the joint between the resistor and the diode.

Step 5: Cut End Off Line Cord

Cut off the plug end of a line cord. Cut the green ground wire and the white neutral a little shorter that the black (120V hot). Strip only the black end and pre-tin the end with solder. Some line cords have a brown, blue and green/yell wire. The brown wire is the "hot" wire.

Step 6: Attach Assembly

Solder the black lead to the resistor end of the assembly.

Step 7: Attach Wire

Solder to the diode end a length of wire with a quick disconnect female connector.

Step 8: Cover With Shrink

Check your wiring and cover with two layers of heat shrink tubing. I used "sticky shrink" (the type with hot melt glue) on the final layer. The sticky shrink makes a damp proof assembly possible.

Step 9: Finished DC Power Supply

This is what it should look like. The generator is ready to have the electrode made.

Step 10: Attach Wire to Electrode

Attach a length of wire to the "electrode" with a pipe clamp to a 4 inch brass nipple with 1/2 inch inside diameter or larger. Use a heavy gauge wire because this will errode away in time too.

Step 11: Add Male Disconnect

Attach a male quick disconnect connector to the other end of the wire.

Step 12: Ready to Install

The completed ion generator with wiring ready to install in your swamp cooler

Step 13: Plugging In

Place the electrode in the water and plug it to the power outlet inside the swamp cooler. I modified the outlet so continuous 120 vac is supplied to the ion generator (bottom outlet), while power for the pump (top outlet) is only on when the fan is on. There is a small tab that joins both top and bottom "hot terminal" of the outlet made to break off with pliers. By keeping the ion generator on all the time keeps the water clean and also allows the electrode to act as a "impressed current anode" to save the cooler from corrosion.

Step 14: Working

The electrode can be placed near the intake of the water pump to allow water to flow though the pipe. Because the bottom of my cooler is epoxy, the electrode can be placed on the bottom without danger of shorting out. You may need to place the electrode on a piece of plastic or other insulating material.

In the photo, you can see "blobs" of something growing in the water, at the pump inlet. This is some type of a bioslime of mold or bacteria that I'm trying to get rid off.
In a few weeks or months I'll check to see if it is still present and see if this device works.

Because current will flow from the electrode (the copper and zinc ions) through the water and return back through the ground, be sure the swamp cooler is properly grounded.

Step 15: Current Is Flowing

Over time, small amounts of the brass will enter the water as ions of copper and zinc and will attack the mold and bacteria. Measured current of .89 milliamps with a meter connected in series with the device. Open circuit voltage is about 60 volts DC.

Step 16: Be Careful !

This Project at my website

Use care when handling the device when on. Remember the device is connected to the mains.

Current is limited, but a small shock may be felt if you touch the electrode, especially if it is wet.

This project should only be attemped with those with experience in electronic project building.



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    42 Discussions


    3 years ago on Introduction

    The brass pipe IS positive if you follow the instructions.

    Step 5 clearly shows a polarized plug and I state to connect the
    resistor and diode to the black wire, the "hot" end.

    Water coolers when properly installed are grounded, so no need to attach the neutral or ground wire. The return current is very small. This makes the setup as simple as it can get.


    3 years ago on Introduction

    Bad plan.

    1.) You instruct to connect the cathode of the diode to the brass you wish to liberate ions from. You've got it backwards. To the extent you succeed in establishing a current flow, you have applied cathodic protection to the brass. It would be less likely to liberate ions than if you had not applied any voltage at all. To liberate ions, you would want the brass pipe to be anodic (+), not cathodic (-).

    2.) There are two wires in the power cord. You said "the line cord is soldered at the resistor end." You didn't say to connect the cord also to anything else. So, assuming you only intended one of the two wires in the cord to be connected to anything, where is there a complete circuit and, therefore, how do you expect to establish any current flow at all?

    3.) You did not specify a polarized plug. Did you intend to connect the brass pipe to white (ground) or black (hot). If you connect it to white and if the pan is metal and grounded, you can have little if any potential develop between the brass pipe and the pan because they are both grounded. If you connect it to black and, again, if the pan is grounded, because you have connected the brass pipe to the cathode of the diode, you have just made the pan anodic and it will corrode at an accelerated rate if you impress a voltage sufficient to overcome the natural electrical potential between the (I assume) dissimilar metals of the pan and the brass pipe.

    4.) You would be more likely to introduce metal ions in the water in the pan by simply placing the brass pipe in the pan and make no electrical connections whatsoever. However, if the pan is metal, to avoid making the pan anodic, you need to know the relative nobility of the pan and brass pipe materials. It would be safer to place a piece of pure zinc in the pan, which would assuredly be anodic relative to the pan. That would not only introduce zinc ions into the water, it would provide cathodic protection to the pan, extending its life. And any resulting current flow would begin and end in the pan. (Current flows to metals in the water supply piping are theoretically possible but, in practice, of no significance as the corrosion effect "throw" is very localized. However, to the extent such a flow did develop, the plumbing system would still be cathodic relative to the zinc so the plumbing system would be benefitted, not harmed.)

    5.) I also advise against connecting 120VAC to such a device (a) for the obvious risk (Murphy's Law) of accidentally leaking significant current or voltage into your plumbing system and (b) because you would be making a modification to your electrical system that would be a violation of the electrical code, which could result in a denial of a claim against your homeowners policy if your device is found to be involved in damage to your home and the insurance company discovers it.

    6.) Due to the above, this is merely theoretical but for you to successfully accomplish your objective of causing ions to enter the water by an impressed voltage, I believe you would need to disconnect the negative lead of your rectifier from the brass pipe and connect it to the pan, if it is metal, or to some piece of metal submerged on the opposite side of the pan as your brass pipe and connect your positive lead to the brass pipe. Furthermore, you would need a full-wave, not a half-wave rectifier or you would never have current flow because the anode and the cathode would never be charged simultaneously. But don't even think about actually doing it. Use the method I described in (4) above instead. (But no guarantee the ions will accomplish your objective of preventing biological contamination.)


    4 years ago on Introduction

    I am glad that I found this piece of information. I am going to implement it in my portable swamp cooler that sits at my bedroom window. I grow tired of needing to continually clean the mold out of it and now I have a remedy, so thank you for this post. I am an electronics technician professionally so I know the "dangers" involved. I have read some others with concern about 120 volts in the cooler, but if there is water there, and if there is a complete pathway to ground to complete the circuit, there should only be maybe about less than 5 volts as measured from the water with respect to ground. Understand that the complete schematic would be Two resistors (actually kinda three if you include the diode resistance) at play here: 1) the 63K ohm resistor and 2) the water/cooler pathway to ground. That second one should theoretically only be but a few ohms at best since water is a great conductor. So if we call our 63K resistor R1 and the water R2 we have a circuit using ohms law that puts R1 in series with R2 with the source being the main AC. So measuring with respect to ground to the source we have of course our 120 Volts. Also measuring from source to the end of R1 we also have close to 120 Volts. However if we measure with respect to ground to the junction of R1/R2 (I.E. the anode) it should be really small and most likely you won't feel a thing.

    Having said all of that, the problem arises if we run out of water. Then we have that full 120 Volt potential at that anode, but guess what? Since we have such a nice current dropping resistor, even that potential in voltage shouldn't pose all that much of a risk either. Why? Because with that resistor in play, there would only be 0.0022 amps of current that could possibly be drawn, or 0.22 Watts. Hardly enough to pose a danger. I hope that clears things up in that department a bit, or you could always use more parts, get that "wall wort" and feel safer too. Either way, I am glad to have found a way to keep the mold at bay.


    7 years ago on Introduction

    Copper does kill bacteria. Its being used in ICU wards to combat bacteria.


    7 years ago on Introduction

    $8.53 at home depot

    DIAL Zinc Evaporative Cooler Anode
    Model # 5157 Store SKU # 341842
    Write The First Review
    $8.53 /EA-Each


    7 years ago on Step 14

    So, has this worked? You mentioned you would check back to see if the green stuff was gone....
    Is the fishy smell gone?


    Reply 12 years ago

    If you are really concerned about shock a GFI can be used. But really, 1/1000 amp is so little. I held on the electrode and dipped my finger in the water. I had to run current through the very tip of my finger just to feel a tingle. A resistor is just about the most reliable electronic component around. Once it is installed, no one will be touching it. a extra ground pad added to the water would insure a ground path, but that would prevent the pan from recieving the protection as an "impressed current cathode" See wikipedi about cathode protection. And about hydrogen production, so little hydrogen is produced that the water alone will absorb hydrogen and there is always ventilation, even with a cover on. I ran the device for a week using a 5k, 5 watt resistor to see what happens to the electrode. Current around 12 milliamps (12 times normal). A blue coating of what I suspect is Copper Hydroxide (mixed with zinc hydroxide) formed on the brass and on the bottom of the cooler. Copper hydroxide has a very low solubility, but copper is present. The bioslime that was there before is changing shape and seems to be dieing off. I now reduced the current to 1/1000 amp I checked on the internet about copper hydroxide and found it is being used as a fungicide. Sounds good to me. Zinc and copper chips are being added to roofing shingles to decompose and form compounds for stopping mold and algae growths. The principle is sound.

    i have a problem with the moldy swamp cooler. i went out of town and when i returned smeltl a sour then checked to see the pads had dark mold. so i throw out the pads, but my concern is the black and pinkish mold in there. now i will drain the cooler to rid it of this. i have read of your invention and planned to implement it...but the fellow that wrote about how unsafe it is. i was wondering about using food grade hydrogen peroxide in the water? would this cure the whole business?

    Peroxide would break down real fast. If you are concerned with the part about plugging into 120 vac, just use a DC wall wort for the power source. Its isolated and low voltage and should not pose a shock hazard.


    Reply 7 years ago on Introduction

    I would like to try this project. I have two "Class 2 transformer" wall wart/worts available: One putting out 4.5V at 600 mA and another putting out 12V at 1800mA. I could also use a battery, but am unsure of voltage required. I know that Positive goes to brass and negative goes to the water reservoir somehow, but how should I go about limiting current to 1 mA? I don't want to overdo it. I don't know how to calculate a resistor to use due to not knowing how much voltage the resistor needs to drop.

    Also, have you noticed any damage to plants due to the water coming out of your cooler with copper and zinc ions in it. I don't know if I need to dispose of the released water in a special way or not. I have heard that steel wool will grab excess copper ions, so could try it in a bucket under the overflow pipe if necessary.

    My main problem is calculating the proper resistor to use for 1mA of current. Thanks for posting this project. It is very interesting. I hope it can help my sometimes fishy evaporative cooler.


    Reply 7 years ago on Introduction

    The calculation of current through the resistor is an Ohms Law thing. Current equals voltage divided by resistance in ohms. The other factor we don't know is the additional resistance of the water path. If you use a 12k resistor with a 12 volt power supply and the resistor shorted to ground through the water path, you would have 1 milliampere. You could get an inexpensive ohmmeter and measure the current or the voltage across the resistor. I got one(digital too!) from Fry's for 5 bucks. For starts try a 10k resistor.

    As far as hurting the plants, copper is actually a required nutrient. I made a bubble lift hydroponic setup for a bell pepper plant. I used bare copper wire in the tubing to allow me to make a stiff bend and hoping the copper would stop algae growth. The plant did fine and the algae just continued to grow. With such low current, the copper ion production is also low. Copper ions quickly form low solubility compounds such as copper hydroxides in the soil, unless your soil is acidic.


    Reply 7 years ago on Introduction

    The resistance of the water path appears to be what I was missing.  I have an older digital multimeter, but it doesn't seem to be sensitive enough to detect current in series with the 10k .25 watt resistor or resistance through the water.  It detects 16.29-16.47 volts from the "12 volt 700 mA" power supply unloaded and 14.22-14.25 volts across the 10k resistor, indicating a current around 1.42 mA.  (I miscopied the transformer's max mA earlier.)

    I have a 1/2" X 6" brass pipe sitting on large a plastic coffee can lid one one side of the pump and several inches of 10 AWG stranded copper wire on the other side to act as a cathode.  I hope ions will get pulled into the pump and circulated.  I couldn't think of a good place to ground the cooler pan, since it's still in good shape.  The paint doesn't appear to conduct well.

    Everything appears to be working as intended.  All components appear to be cool.  Is the quarter watt resistor strong enough tolerate the load?  Do you think ~1.43 mA is too much current?  The pan holds close to ten gallons, but I don't have a purge pump or bleed off system.  My soil is basic, so I'm glad to hear about the low solubility copper compounds.  Thanks for all of the help.


    Reply 7 years ago on Introduction

    Calculating power is easy. Its simply volts times current. So 1.43 milliamps times 14.25 volts is 20.3 milliwatts. I always run a resistor at halve its rating or less. In this case 125 milliwatts for a 1/4 watt resistor. So your good to go. The low current should be more than enough. The ions will quickly form low solubility compounds in the water too. Anymore would just be in excess. Try it in a cup of water (not one for drinking later, use a disposable cup) with a lower value of resistor and you can see a pale green precipitate form. This is copper hydroxide. Add vinegar and the precipitate will turn to soluble copper acetate ,which is toxic, so dispose carefully.


    Reply 7 years ago on Introduction

    I'm glad to hear about sufficient power dissipation and current.  After having the ion generator running for about a week in the same water with no circulation (due to cooler weather and lack of A/C use), a precipitate has formed under the brass pipe.  It's good to know that the water will only hold needed ions.  The precipitate appears to be pale green.  I didn't test its texture, but copper hydroxide definitely makes sense.  I appreciate the update.


    Reply 7 years ago on Introduction

    I found a patent for a device that releases copper ions to kill mold and bacteria using a current flow of a few milliamps like what we are doing.

    You should clean it with bleach. In our coolers we put bromine tablets (like from a hot tub) in ours and it seems to work very well it got rid of the fish smell in about 30 minutes. (but is smells a little like the chemical) good luck

    i have figured it out per my i am adding a purge pump that lets old water out every 8 hours thus eliminating mold!

    Its a pretty much standard thing to let a little water out when it is running. This will keep down the mineral buildup from evaporation. A hose connects to the recirculation pump with a valve. I let out about a gallon per hour. Total purging, that's a great idea.