I knew the electrodes would be a PITA and I have been putting the task off a bit. Today I decided to apply a bit of effort and get this critical task done.

One think I learned from previous runs is that pure titanium is a crappy conductor. It works, but not as good as copper, and tends to heat quite a bit if the amperage is high. The typical titanium cathode from suppliers like Nothstar has a 1/2" X 1/16" shank, and above 20 amps, will heat badly; enough to boil water.

I decided to try a test with my power supply. I cut a 1" wide by 0.062" thick strip of Ti and wired it into my supply. Kids, don't try this at home unless your power supply is intelligent and can current limit.

I dialed in amperage until the strip became uncomfortably hot. This took place at about 40 amps... not high enough. It means I needed a LARGER Ti cross-section for the cathode. I cut another strip exactly the same size, doubling the cross-section. This handled 60 amps with ease, and with a bit of air cooling from a fan, which I planned on doing anyhow, it'll do 80 amps.

Now I have two big strips of Ti that must be routed from inside the EC for electrical hookup. Quite a bit of fiddling and thought later, and I had it. By bending them 90 degrees, cutting two slots on the lid, and adding a CPVC ring that would press against the viton o-ring, I was able to expose the two Ti cathode tabs. These will be tied externally with a thick Cu cable.

Gluing the ring in place, which will secure the cathodes, will be one of the last things I do, as I cannot work on the lid with two big cathodes hanging off of it. Holes will be drilled in the Ti tabs to accept the power supply cables.

What remains: the anode. I was very impressed with the conductivity of the MMO coating on the anode. Even at 60 amps, the anode remained relatively cool, even though the bulk of the anode is Ti, the same as the cathode. It is the MMO coating that is carrying the bulk of the current.

Days ago, I bored a hole in the lid, and in my lathe, turned a plug that will fit nicely into this hole. I have plenty of CPVC round stock, so I can turn additional plugs, which I call "carriers", for various anode types. Note the o-ring groove in the plug. The anode will be sandwiched between the two cathode plates.

Once I figure out how to secure the anode, this thing will be ready for a trial run. It is very important that this EC (Electrode Cell) be completely water and airtight, with the sole exception of the vent. I anticipate the electrolye level possibly being above the level of the lid, and climbing into the vent tower, which I mentioned in the last blog entry. All of this will depend upon the pump. The pump volume will be predicated upon the heat generated in the EC. If the EC heats up too much, I'll need to increase pump velocity. If not enough, the pump must be reduced. My goal is 65 to 85 degrees C. for the EC.

Part of the process is checking the pump function. I know the tubing can handle the chemistry of this system; all that remained is to see how durable the tubing is in the peristaltic pump head. I think tentacles is right, a centrifugal pump is probably better, but this pump is what I bought (cheap) on ebay, so I want to put it to use.

It's been running for two days now. At the end of the test run, I'll check the tubing inside the pump head that is being abused by the peristaltic rollers, and see if it has suffered much. I am having nightmares about this system letting go, developing a leak in the plumbing, and dropping GALLONS of hot, caustic, chlorinated electrolyte onto my shop floor.

An example of how noxious it is... I have been collecting used electrolyte in a big jug. Today, I opened it and poured about a quart into a big beaker to see how it would attack various plastics. Even days after a run, the water is so laden with chlorine that I nearly lost it after getting a strong whiff. I ended up staggering away, exhaling hard (and not inhaling) to get away from it. It was THAT BAD. This system MUST have integrity.

It has been a long road, but I'm near the end. One of the important things I've learned is that if you want real production, you must take the cross-section of the electrodes into account. If they are too small, they WILL heat badly, easily enough to melt the plastic that is supposed to be providing support!