New Smart Instant On Water Heater

[rsjsouza]

@amyk, loved these pictures! I've seen my share of crazy installations and I wish I had a camera then...

[Zero999]

the main thing i would be pondering with current passing between electrodes in an electrolyte would be corrosion over time, be it one plate to another, or the pipe to the electrodes...

also... it seems it would be dumping current into most houses earthing system.. which i see as a problem, unless its isolated somehow, but still seems difficult then as there would be 2 electrodes, so 1 would pass some current to earth relative to the other...

It's an electrode heater which also been around for years. The only novel thing seems to be it's being used for instant heating.

Corrosion isn't much of a problem with AC because the current changes direction before the ions have time to migrate through the solution.

You're right about some current going through the earth but it'/s not that bad because the neutral is positioned to minimise earth leakage. There are special wiring requirements for electrode water heaters in the UK. I don't know about the US. I'd imagine that using an isolation transformer would eliminate the earth leakage and special wiring requirements.

[SeanB]

With the cost of an isolating transformer for 5kVA plus i would buy a heating element and geyser every year and still come out ahead. In most cases electrode boilers are designed to have a good earth connection, as there will be current flow there. The most common use I have seen is a 3 phase unit used to make steam for use in a plant, where it uses a 380V 3 phase supply, at around 60A per phase, so as to generate a very fast reacting steam supply that is much smaller than a standard oil or coal burner, and without needing a large oil tank or coal bunker. They are meant for permanent installation, with a earth current monitor that will trip at the amp level, for phase faults.

For a domestic instant water heater it is more likely that it uses a high density heating element, with a spiral wound element exposed to the water flow. A short life for the element because of temperature cycling, and the actual resistance wire runs at probably close to white hot to get the heat flow across the MgO insulation high enough to heat water fast. The only domestic electrode boilers I have seen are clothes steamers, which need a salt dose to run, and which are double insulated, with water filling being done only when disconnected from the mains.

[NiHaoMike]

Might it be possible (probably not practical for general use) to use a high frequency AC output switching power supply to provide the isolation? With a high enough frequency, it might even be possible to capacitively couple through the glass or whatever. Seems like something that could be useful for heating corrosive liquids.

[SeanB]

You can buy that off the shelf, in a box labelled "Microwave oven". At lower frequency you use a big one to heat metal for recycling. If you build it big enough you use plain mains as the frequency source, and it uses megawatt power levels for smelting steel.

[Zero999]

With the cost of an isolating transformer for 5kVA plus i would buy a heating element and geyser every year and still come out ahead.

An electronic transformer, similar to the sort used for halogen lighting, would be much cheaper. The output waveform doesn't need to be pretty, all it needs to do is put a high enough voltage though the water to heat it to the desired temperature.

It has a microcontroller anyway so I wouldn't be surprised if it controls a pair of IGBTs/MOSFETs connected to a high frequency transformer, forming a SMPS similar to that of an induction hob.

[rsjsouza]

Found a good one at my mother in law's home.

Fortunately this bathroom is being used as a deposit, and not for showering...

In any case, I asked her to remove everything in case anyone has any "brilliant ideas"...