Plumbing Power

Scavenge power from indoor plumbing

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This project aims to scavenge power from water flowing through home water supply lines. A cheap off-the-shelf turbine generator and a custom energy harvesting and storage circuit form a module for running micro-power devices from otherwise wasted energy.

There's power in your pipes.  Water flows out of the tap for a reason - it's seeking a lower energy state.  Unless it just dribbles, there's more energy than you need to get the water out.  What happens to that energy?  The water splashing around in the sink or toilet tank gets a little warmer - a total waste.  I'd like to make a power-scavenging module to harvest some of that energy to make it available for low-power devices.

Some possible applications of this module include powering:

  • Wireless thermometers/thermostats
  • Nano-power lighting for nighttime bathroom trips
  • Low-power IoT nodes, such as frozen-pipe sensors

These devices could be placed anywhere there is running water, such as:

  • Under sinks
  • Behind toilet tanks
  • At outside hose bibbs

The generator and turbine for this project are available commercially, for example on ebay.

The specs say that the generator will start running at 0.05 Mpa.  Common household water pressure is between 0.25 and 0.5 Mpa, so it should have no problem spinning the thing up.  Since the water flow will be intermittent (like whenever filling the tank after a toilet flush), the controller will need to store the generated power for later use by the end system.

I envision a two-stage power storage system.  Since the generator will create short bursts of relatively high power, a storage device with a high power density is needed.  Supercapacitors have a high power density, so can quickly store the energy bursts, but unfortunately are plagued with high self-discharge.  To avoid losing energy to self-discharge in the caps, the controller will then charge secondary storage batteries.  These batteries are much better suited to long-term storage than capacitors.  In the unlikely event of a long period of disuse, the controller can use a primary lithium backup battery to power the device.

The goal is to build a power module that can be used for various applications.  The interface will include the power rail, enable/shutdown control, and a power status/state-of-charge indicator.  The powered system can use all or none of these interfaces as required.

The idea of using running water for power generation is hardly an original one.  The first hydroelectric generator was installed in 1878 (Wikipedia).  More recently some municipalities have started generating power from their gravity-fed water supplies.  Closer to home, @Vije Miller created a shower-generator for charging batteries for the coin cell challenge: #Coin Cell Challenge (1) Shower Battery Charger.

  • Free project to a good home

    Ted Yapo06/05/2018 at 12:52 0 comments

    I started this project with thoughts of entering into the power harvesting challenge, but I'm just not feeling the joy - too many other things to work on at the moment.  So, I'm offering the project to anyone who wants to run with it.  I can supply two generators ("5V" "12V" versions) and a coupler that fits a standard shower hose.  I'll ship these parts to you for free, using up to the amount of seed money this project garnered in the community vote of the first round (TBD).  This will probably cover any shipping within the U.S., but international shipping might be a little more.

    I think this project has potential, and it's not really an original idea of mine, so I'd hate for it not to be explored during the contest just because I'm off working on something else.

    If this interests you at all,  or you have another suggestion for the project, let me know!

  • Backup Power Architecture

    Ted Yapo04/22/2018 at 15:01 0 comments

    For some applications, a backup power source will be desired for periods of low water use.  An example might be an IoT frozen pipe sensor, which should continue to work even if you are not running the water often enough to charge the batteries.

    I envision a power-switching circuit to cut over to a lithium primary battery during such periods of "power drought."  The simplest way to accomplish this is with the use of two Schottky diodes:

    The problem with this circuit is that the forward voltage drop of the diodes reduces the battery life.  Although for very low current drains, this may be sufficient, for any application which requires periodic high pulse currents, the forward voltage drop becomes a limiting factor.  Additionally, the reverse leakage of Schottky diodes can be relatively large, causing unnecessary power drain.

    A more efficient solution can be constructed with any number of commercial "smart diodes" or power-ORing ICs developed specifically for this purpose.  These devices use a comparator to determine which input voltage to use, and switch MOSFETs to efficiently select the appropriate supply.  Although these devices can be more efficient than a simple diode-based solution, the added efficiency comes with added cost and complexity.

    I'm currently surveying the offerings from various manufacturers to determine if any of them are suitable for this power supply module.  It may be that the module can be designed to accept either a simple diode-based switch or a more sophisticated IC-based solution for different end uses.

    At this point, I haven't ruled out the possibility of designing my own ideal diode controller for power switching.  Although a circuit constructed from individual comparators and MOSFETs probably couldn't compete with commercial offerings on price, comparators and other components may come for free as peripherals on a microcontroller.  In this case, a home-brewed solution might make sense.

  • Down the rabbit hole

    Ted Yapo03/24/2018 at 00:02 0 comments

    When manufacturers use security fasteners on a device (like on a hard drive), they're saying they don't want you to open it.  When they use Phillips, I can only assume you're supposed to tear the thing apart.  So, guess what happened a few minutes after this arrived in the mailbox?

    There was minimal documentation on ebay about what these things actually are, but they came in 5V and 12V versions.  I bought one of each (from different vendors), and the 12V happened to arrive first.  I figured they were probably wound with a different number of turns or something like that to produce different output voltages.  Imagine my surprise on opening the case and finding this:

    The 9 coils are wired as a 3-phase generator and there's a circuit board in there!  OK, time to figure out what it does.  I couldn't get the whole PCB into the frame of the inspection microscope, so I stitched this image (poorly) from two shots:

    The three red wires on the left come from the coils.  The six SOD-123's are obviously diodes of some sort in a 3-phase bridge rectifier.  It turns out "A7" is a common code for SMD packages.  These could be 1N4007 A7's.  If so, replacement with appropriately-rated Schottky's might improve efficiency.  I'll measure the forward drop after removing one from the PCB.

    From what I can tell, this is the circuit:

    I'm assuming the glass diode is a zener since it is reverse-biased by the 2k7 resistor.  The SOT23 appears to be a SS8050LT1 NPN transistor, while the larger TO-252 a power NPN, MJD41C.  It seems fitting that I was only able to decode the component markings after searching on ebay, where I bought the mystery generator in the first place...

    Anyway, this looks like a crude zener-based voltage regulator for charging 12V batteries.  When I get a chance, I'll re-assemble and test it.  In the end, I'll probably end up tossing this PCB and replacing it with something more suited to my end goals.

    The other side of the assembly shows the turbine itself:

    I'm not sure how well sealed this whole thing is or if the plastic is food-safe (doubtful!) and I noticed some tiny solder balls on the PCB, so I'm thinking for now I'll keep it out of the potable water lines.

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Ted Yapo wrote 03/25/2018 at 17:32 point

I was going to put it in a braided flex line for now.  The line already has some crazy curve to it.

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Dr. Cockroach wrote 03/23/2018 at 13:03 point

Another use might be in the down spout of a home roof rain gutter system if there is enough rainfall to make it practical. Just have to make sure that leaves are filtered out first.

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Ted Yapo wrote 03/23/2018 at 16:11 point

That's an interesting idea. The ebay listing says the turbine will start running at 0.05 MPa of pressure.  This equates to a column of water 5m high, so I think your gutter would need to be this high above the generator to ensure it starts spinning from a stop.  You might get away with less if the water had a running start (pun intended), but reliability could be an issue.

So, yeah, if you have a taller house it could work.

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Dr. Cockroach wrote 03/23/2018 at 17:18 point

Almost all beach homes on this coast are at or over the 15m height but different  parts of the country will have more rainfall over others...

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Dr. Cockroach wrote 03/23/2018 at 17:54 point

@Vije Miller I was thinking more like the pacific north west where it rains a lot. But then it was just an out of the box idea plus the rain water can still be collected :-)

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Morning.Star wrote 03/23/2018 at 06:51 point

Why not use the water directly for power? It has permanent pressure...
Years go I had a garden and grew veg in it, but the local cats decided they wanted it for a toilet and a battle of wits ensued.
Garlic granules, orange peel, utlrasonics all failed (one of the cats actually crapped right in front of the ultrasonic, not amused) so I went all opposable thumb on the dirty buggers and installed a sprinkler with a washing-machine valve and a PIR. That moved them to where it didnt reach, so my next plan was to make it patrol the fence using the water pressure to drive the machine and water the veg at the same time.
Obviously, I neve completed it - dont have a garden now - but the idea is still sound. I had the idea to power the electronics from a generator onboard the mechanism, so it just had a hose for supply... ;-)

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Ted Yapo wrote 03/23/2018 at 11:42 point

I know of two devices which use the water power directly.  One, which I have installed here, uses the pressure to run a reverse osmosis system for purifying your drinking water.  Some consider them wasteful because they create a lot of wastewater in the process of purification, but our drinking water is soooo bad (always right at the EPA limit for TDS) that it doesn't get consumed otherwise.

The other one, which I am considering installing, is a backup sump pump which uses supply water pressure to pump out your basement in case of electrical power failure.  The alternative technology is storage batteries which need periodic replacement..

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Morning.Star wrote 03/25/2018 at 06:59 point

That is pushing the envelope a little, Ted, but it reveals the flaw in our technologies. We dont actually use energy. Free or otherwise, even though fuel still lays around in abundance... What we do use, is something that can never be recycled. Force...

Everything we have, no matter how technical or green [and everything in between] uses a force to drive it. A magnet, an explosion, hydroelectrics, a sail, a solar panel, even walking around is driven by forces. Nuclear 'energy' is made by a giant steam engine powered by a controlled critical mass [Its the word controlled scares me...] so ultimately is a force too.

I sure hope you didnt dig your basement yourself, lol, because humans for some reason have chosen to fight most of the natural forces we encounter rather than deflect and use them, and a sump pump is a classic. Ignoring why your basement is underground in the first place ;-) that also means you are using an equal amount of water to what's being pumped, assuming 100% efficiency of the pump and driver. [Close, if it's a piston...]

That boils down though, to having tanks above ground to collect the rainwater needed to pump out the holes dug in the ground under the tanks. Typically human over-engineering if ever I saw it lol, we should never have left the trees IMO. XD

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