Must it be Waterproof?
Before you decide to waterproof something by potting it in epoxy or building a housing for it, make sure that it really needs to be waterproofed. It was sure a surprised me, but most DC motors will run just fine completely flooded with water, even salt water. All sorts of DC electronics will work without any protection, including solenoids, linier actuators, reed switches, and toggle switches. Now if you can protect these things from water then they will certainly last longer, but it good to know that if water does find its way end the it is not going necessarily cause an immediate failure.
Many of the components especially capacitors which contain air pockets will not survive even moderate pressure changes at 10 feet. Harbor Branch Oceanographic actually did test on components in the hopes of avoiding the need for pressure resistant housings or entombing a board in epoxy.
For electronics under water there are two basic choices. (1) Build a water and pressure tight enclosure. (2) Or encase the electronics in epoxy or some other goo or potting.
For cameras and boards that you have to access in order to adjust or exchange parts, a water and pressure proof or 1 atmosphere (1 ATM) housing will likely be the best choice, so you can keep the view port unobstructed and open the housing to easily access the parts. See Build a Waterproof Housing on below.
You can buy "real" potting compound for around $50 a pint and at that price you know that I've never tried "real" potting compound. But there are several alternatives including Epoxy, Polyurethane, RTV Silicon, and even wax. Each of them will meet a different need and making the choice is half the work.
Epoxy, Polyester and Vinyl Ester
(2) Epoxy comes in two parts and it starts hardening once they are mixed. The hardware stores will commonly carry an assortment of epoxy. If you only need a little then the fast drying epoxy in tubes works great. If you need more volume or if you need to reinforce the exterior of the part then the hardware and auto parts will have fiberglass repair kits frequently under the Bondo brand name. These are most likely Polyester or Vinyl Ester resins and not the more expensive Epoxy. The resin is optionally used with fiberglass cloth, and when are when a few layers of cloth are added it will make a very hard shell. Getting it to look pretty is not easy and requires lots sanding a filler putty, but it does not need to be pretty to be water proof. Be sure to pick up some disposable bristle brushes and latex gloves. This stuff is a mess to work with. These resins typically have stay liquid for more that 15 minutes, and they can be cut with a knife an hour or more later while they are still soft. This is a good time to trim off the drips and excess. (3) I use fiberglass with epoxy to seal up the motor on linear actuators. (4) and to secure better lip seals to the shaft housing of a linear actuator. Masking tape can is used to keep the resin off the shaft and it is easily cut before it hardens.
(5) If your going to use a lot of epoxy then it is much cheaper to buy it in larger quantities. A 1 1/2 gallon kit of epoxy and pumps cost about $80 from www.jgreer.com The kit comes with pumps so mixing up a small batch is as easy as 1 pump from the catalyst jug for every 2 pumps from the larger resin jug. That goes into a zip lock bag and is squishing it around until it is mixed and then it is poured out.
(6) (7) To seal my "Watt's Up" amp hour meter I cut a piece of 1/4 inch thick acrylic for the face plate, and glued it to the frame of the LCD display with RTV Sealant from the auto parts store. RTV is also used to temporarily hold more acrylic pieces in place that form a mold. Once the RTV is dry the mold is filled with epoxy and allowed to set. I made a clay dike around the negative wires used to measure the amps and the shunt they are soldered to.
Plastic bags and clay from the craft store are easy ways to make a quick mold around a part that you want to pot. To pot a 100 amp solenoid relay I first sealed any small holes with RTV gasket sealer, then I put the solenoid down in a zip lock bag and warped it with tape to keep it somewhat conformed to the shape of the solenoid. I filed the bag with epoxy and set it aside to dry. Once dry the tape and plastic bag peal off. It's easiest to do this when the epoxy is still soft because you can use a box knife to trim off the bulges that are not needed and make it look a little less like Frankenstein. The next step was to roll out some clay and make a mold around the wire terminals on one side and then fill that with a second batch of epoxy. (8) Finally as show in the photo a clay mold was fashioned for the other side of the terminals and that was filled. (9) The completed part is ugly, but durable and waterproof.
(10) When potting larger parts like the speed controllers for the trolling motors, I add talc. Talc will stiffen the resin and if you add more talk than resin it will be more like a tick paste or even a putty. Adding talc also stretches your epoxy and saves you money. Wood flower, aka: fine saw dust also works as well as talc. If your belt sander has a collection bag then you already have a ready source for wood flower.
Talc and wood flour will also reduce the amount of shrinkage
as the epoxy hardens. Too much shrinkage can crush a
component. If the epoxy will be more that 3/4 inch thick then
it is also a good idea to completely cover the part with a first
layer and allow that to harden. Then fill to moldwith a second
One Word for You; "Plastics"
This stuff is great for making your own plastic parts, and potting. You get two gallons for $70 on eBay and other outlets or directly from www.dascarplastics.com
Just look for "Dascar Plastic RP-40". Its a two part polyurethane cures rock hard and it does it in minutes! Warning: it gets hot, and the thicker your part the hotter it gets, so use it in layers for larger parts that can't take 140 degrees. It also shrinks so use two pours if you are potting something fragile.
I doesn't have any odor. It acts more like a really fast setting epoxy. But it's a lot thinner than any epoxy I have used so it has less bubbles and it really gets into the cracks. It does not have the glue like quality of epoxy. I poured some out onto a steel table and once it cured it was easy to lift off with a chisel. Epoxy on that table would need to be hammered to make it break loose. It's got more grip that two part RTV Silicone but not much more. I use it in the video to fasten a hose to the hull and it would not have worked without embedding the screws to provide a mechanical connection.
(1) (2) RTV Silicon comes in to a two part mix and you can also buy it in tubes at the auto parts store. These are very different products. The two part RTV is intended for making molds but is good for reusable gaskets. The automotive RTV sticks to surfaces so it seals without being compressed but remains soft so unlike epoxy it can be easily removed with a knife or scraper.
Two Part RTV Silicon
The two part mix like epoxy comes in two parts, that are mixed together. It will not stick to anything so left on it's own it only makes a splash proof seal. But it is great if you need a strain relief or if you need a reusable gasket that will be compressed in order to make a seal. You can buy RTV silicone from www.jgreer.com for about $60 for 1/2 gallon.
(3) (4) I used two part RTV to seal the wires going into the helm control box. This box will be exposed to water but not routinely submerged. wires entering the box were first sealed with automotive RTV Silicon gasket sealer just to plug the hole so that the two-part RTV would not leak out. The RTV in a tube is more like tooth paste and the two part RTV is like pancake syrup.
I used a piece of duct tape to close up the side and make a mold that could contain the two part RTV. With the mold filled it was just left to dry overnight.
Connecting a Bunch of Wires
(5) Big wiring projects like the wiring harness for the submarine
will have lots of wires that all need to be connected. A bus
bar would normally be used but that would be a pain to waterproof so
instead I used 1/2" copper end caps as solder lugs and incased those
in PVC and RTV.
(6) To insulate the connection, a short piece of 1" PVC is cut and one end taped closed in order to form a mold around the copper cap for RTV. (7) The RTV is mixed and poured into the PVC mold and worked so that it flows under the cap as well as in between the wires. If needed the PVC and RTV can be cut away, and the cap heated so that a wire can be removed or added.
Not as soft or easy to remove as RTV, and not hard as epoxy. Goop is available at hardware stores like Home Depot under the names "Plumbing Goop", "Household Goop", "Automotive Goop" etc, but it's all the same Goop. It goes on and dries clear and can be cut away with effort if needed.
. It's great for water proofing around wires where they pass through PVC, aluminum or acrylic.
Sometimes epoxy is no good because you want to be able to replace a part and RTV is no good because the pressure it high or the part is so large that you don't want to spend that much money. That is when candle wax is a good choice. The only real problem with wax is that a hot day can turn it turn it back to a liquid.
(1) However machineable wax that is designed for prototype work with a mill or lathe softens around 230 degrees and it is much harder the regular candle wax. You can get machineable wax from www.machinablewax.com or www.freemansupply.com. A 2 in. x 6 in. x 18 piece is about $50.
(2) I you want to save some money, you can make your own machineable wax by melting polyethylene plastic into candle wax. This is not a good long term solution. After 2 years the homemade plastic wax I used became brittle and cracked, allowing water in. This will be less likely to be a problem if the part being potted is small and there is less contraction in the material.
To make your own machineable wax, pick up a role of polyethylene plastic and gather some old candles. I pilfered some of Kay's candles that were almost at the end of their life.
I am certain it will depend on the actual type of polyethylene plastic you use, but a mixture of 1 part plastic to 4 parts wax and by weight was enough to raise the melting point to 170 degrees, an 80 degree increase. It also makes the wax much harder..
Do be careful. If you think hot wax is painful, just wait until you get some molten plastic on you. Also candle wax becomes very flammable when it is hot enough to melt the polyethylene plastic, so do this outdoors with a lid to cover the pot when it burst into flames.
(4) I used my first batch of machineable wax to waterproof a box that contains power relays which control the winch. (5) A little duct tape was used to seal around the power cables and then the box was filled with molten machineable wax.
If needed the mixture can be removed by patiently melting it with a torch. It takes about 3 hours to remove 3 pints. I know this because I failed to sufficiently tighten the ground wire screw and before I poured the wax into the box. And the wax managed to isolated the wire and stop it the wench from working!
(6) The box was 3 inches deep and the wax failed after 5 years as it became brittle and cracked.
(7) You can also use machineable wax for it's
intended purpose which is making prototype parts or in my case
making a model of a part the will be cast in aluminum.
Keeping water out is often just a matter of adding a gasket. I use automotive RTV, rubberized cork gasket material from the auto parts store for small items. (1) For bigger items I often use 1/4" neoprene. You can buy it from industrial supply houses or McMaster.com where I got mine. It cuts easy with scissors or a box knife and glued down with rubber contact cement. It will crush and not expand back to it's original thickness. It also is easy to tear, but also easy to repair with a patch piece and more rubber cement.
RTV Silicone Gasket
Automotive RTV is great for permanent gaskets as it is intended, but you can also make reusable gaskets with it. You'll normally find in the small tooth paste like tubes, but it also comes in calking gun size tubes which sell for around $15. My neighbor Travis recommended this method for making a reusable RTV gasket so I gave it a test.
I need a reusable gasket in the hatch which is repeatedly opened and closed. (2) You use wax paper between the two parts so the RTV only sticks to one side. I used a spray adhesive to help tack the wax paper in place, the laid down a bead of RTV. (3) Then gently pressed the parts together. (4) After 30 minutes the parts can be separated allowing the RTV to cure faster. Do not try to removed the wax paper. (5) Let the RTV dry 24 hours first, and then the wax paper will peal off without lifting the gasket. (6) Finally, trim away the excess RTV.
(7) RTV is a soft material and it does not take much abrasion to peel up the edge. So I roughened the aluminum up with a rasp and made another test piece. (8) This did help but it also helped to trim the gasket back from the edge of the aluminum and trim it at an angle. Both make it more difficult to peel up. When it did peel away from the aluminum it stretched and did not easily tear and it would fall back in place where it would still be usable.
Cameras, Lights, and other electric equipment may be best protected in a pressure resistant housing. This quick and easy to build housing has been tested down to 700 feet. (1) My friend David Bartsch came up with this and it is the same housing he uses on with his home made hydrophone. You can read all about David's hydrophone work here: Hydrophone
(2) The body is a 1 1/2 inch PVC Sch40 coupler. And the cleaver trick is to insert two short pieces of pipe that only stick out about 3mm (1/8 inch). These pipes will form a shoulder for a size 327 o-ring that is the same diameter as the coupler and about 5mm (3/16) thick. Some couplers have raised lettering on the ends that needs to be sanded smooth first.
To properly fit the shot pipes inside the coupler, insert the pipe segments into the coupler starting with pieces that are longer that needed. No glue is needed. Just seat the pipes all the way into the coupler. Then use a marker and mark a line about 1/4" from the coupler, all the way around each pipe. Then insert the coupler with the pipes into a vice and use a hacksaw to cut along the marked line line. Finish the cut edge of the pipe so that it protrudes 3mm (1/8 inch) from the coupler, using a belt sander or sanding block. Clean the part before seating the o-ring to pervert contamination. Install the size 327 o-rings by rolling them backwards. They will be a little smaller than the pipe.
(3) (4) The ends are a 5mm (3/16") piece of acrylic and a 2mm (1/16") piece of aluminum. It is best for any wiring to pass thought a hole in the aluminum. Drilling a hole in the center of acrylic will make the acrylic more likely to crack. The aluminum is also a great heat conductor and helps keep any electronics inside cooler.
(5) David cuts the aluminum with a a 3 1/4" diameter (83mm) hole saw. Anything smaller will not allow enough room for the mounting bolts to clear the o-ring. A jig saw will also cut aluminum as well as acrylic. (6) The bolts are 3 inch long x 1/4 inch stainless steel with flat washers and a nut. Don't over tighten them, just snug them down so can move them with your fingers. Wing nuts work great if you need to open the housing frequently and without tools. (3) When looking at the o-ring thru the acrylic you will see a darkened ring begin to appear in the center of this o-ring as you tighten the bolts. Although not visible, the same thing is happening on the surface to the aluminum disk. This dark line or seal point should get to be 3mm thick to ensures a good water tight seal on both wafers.
(6) A plumbing compressing fitting selected to fit the hole in the aluminum and the cable. If the cable fits tight through the hole then it is not necessary to use a compression fitting. Just use plumbers Goop on both sides of the hole.
(7)(8)(9) There are lots of cameras on the market. Many have there own inferred LED lighting built in. For best results the lighting for under water camera should be mounted away from the camera so that small floating objects directly in front of the camera are not light up, which caused backscatter.
(10) The housing also makes a great light fixture. Extra long couplers are available at more hardware stores, or you can simply glue together 2 couplers, and use all-thread rods if needed. David is using the LED lights removed from a flash light. LED's not only require little power and last many hours, the also are cool burning so they will not over heat the PVC housing or acrylic.
Goos, Goops, and Glues for Sealing and Waterproofing
We tested a variety for common goos, sealers, glues and silicones looking for a few that worked really well for sealing and waterproofing DIY projects. This video is what we found.
If you need to go down to 100 feet or less then a simple idea is to just buy and OtterBox and add the wire connections you need and epoxy those in place. For less than $15, you'll have a reliable, easy to open case. And OtterBoxes come in clear plastic so you can easily check for leaks and see the instruments inside. You could even use it for a camera case.
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