How to make my own power plant. The story about the rabbit hole

The reason for why I ended up in this mad house is that I last spring got a sick leave from work. Things had been very rough for a long period, and at one point my doctor gave me a sick leave for quite a while. (I appreciate our scandinavian welfare system!)

During this period I had to come up with some kind of project, not to sit on my behind and sulk.

I came up with the insane idea of making a water wheel in a small creek river next to our house, to generate electricity, to charge my bike. I tried to make one in waterproofed construction wood (for decks and such), but it was way too huge and clunky and impractical for the little creek.

I then asked a friend of mine who is a engineer in “waterpipes(?)”: How can I make a smaller type of wheel in a way that is techincally precise enough not to wobble and fall apart right away?

He said: you have to find some sheets of plastic and CNC them. I asked him: What is a CNC? And that was when I fell down the rabbit hole. I quickly came across MPCNC, and then I had to figure out: “How does a 3d printer work?” And the rest is history.

WELL - back to the water whell. I still don’t have much clue about electronics… how can I make such an apparatus, on the electronics side? My plan is to get a dynamo from a car, that has a built in 12v regulator. Is it as simple as connecting the 12v generator to a 12dc to 220 ac converter?? Is that it??


If you get an old one, like from the 60s or 70s, that might work. The new ones require a voltage input to get into business.

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Any idea about what voltage and current, for the newer ones? Could run a little line back from a battery if needed.

That’d work, your car sends current to the field terminal of the alternator in a similar fashion. I think the big issue may be if a water wheel can turn a car alternator fast enough. You may need need belt, chain, gears to up the speed.


Yes, I imagine some kind of gear system. It only depends if there’s enough water, to make the right torque. My waterways-engineer-friend says the stream we’ve got can produce 400W (I have NOO idea how he makes such estimates from eyeballing)

IIRC a car alternator should be around 80W or so, sounds like you’d have enough power. Maybe try to find a chart giving alternator output vs. RPM? I have a Bosch Automotive Handbook, if there’s anything useful in it I’ll post.

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Ah - an alternator would not be able to deliver more than 80W, at all?

I think you can get 60-100 amps out of oem alternators, depending on the model. Should be regulated to right around 14.5 volts.
I recall reading that most alternators require somewhere between 2-5hp to deliver the maximum output.


I found a converter that has a tolerance from 10 to 15.5V on input. I guess that 14.5 would work?

You’re right. My bad, I was thinking watts rather than amps. Brain fart, I used to work testing warranty parts for a manufacturer, alternators among them, I should’ve known better.

BTW, nothing in the Bosch book, just an unquantified chart showing alternator output changing discharge to charge at an unspecified RPM.

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Should be fine. I did find this:" Alternator may not generate sufficient charging voltage until alternator speed is greater than about 2000 RPM . Typically, alternators have their full output rated at 6000 RPM but can continue to spin up to 12,000 RPM or more without any additional increase in output ."


Aaai aai aai! I see that my main concern should be making a kind of gear system that can survive for longer that 5 minutes… the electronics are the least of my concerns.
Thanks a lot for the numbers!!


Given the watery environment, pulleys and a belt may be less maintenance intensive and a little easier to change ratios if needed.


why not just embed magnets into the outer ring of the waterwheel and then build a stationary wire coil to convert the changing magnetic fields into your voltage output?

Alternatively, any 12v DC motor can be used to create electricity. You’ll have to use gearing and try different motors until you find one that can produce the output you’re wanting to get.

In either case, you’ll need some type of circuitry to take that 12V output and buffer/clean it so that you can use it in charging your bike.


Have you looked at Free power- How to convert an old washing machine into a water powered generator?

I was thinking some DIY wrapped stators and a handmade Tesla Turbine…

You people make my head go snap crackle pop!

I salvaged the motor from a faulty washing machine (the bearings was the culprit, made it sound like a jet engine). It runs on 190 V, not quite sure how to make it to 220v or to a battery friendly voltage (12/24v) It’s also “three phased” (right term?), and that also makes my brain fizzle.

I also have got an old motor from a hard drive from the 70ies. It’s super heavy, and the wires spark very easily, it’s almost enough to stare at it angrily long enough. But this one says 50V DC. Also boggles my mind.
Edit: can such a fella be of help: ??

The reason for why I’ve been considering an alternator is that it’s very convenient if it delivers something resembling 12v, that would make everything more simple (but what do I know??)

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Aha! A rectifier! Very very interesting. I think I have a smiliar amount of water running. But I wouldn’t be able to run a long enough pipe to get the pressure up like this. I’d have to use a heavier type of wheel with a lot of torque, and increase RPM with gears/belts.

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The turbine will have some maximum speed it will turn when it has no load and it is just freewheeling in the water. And similarly for any given motor/generator, there is some maximum speed beyond which you wouldn’t feel comfortable running for long periods without it wearing out, or there is some maximum speed above which the voltage is higher than you want to deal with (perhaps the maximum that your buck converter can handle).

If you hook up a pulley or gear system to match the no-load speed of the turbine with the maximum speed of the motor, or if you just select a motor that works at the speed of the turbine, then add a rectifier and buck converter to drop down to your desired output DC, you should be in pretty good shape.

As a reminder: speed is proportional to voltage and torque is proportional to current.

When the electrical output circuit has no load, there will be no current flowing through the generator and the generator will provide no resistance to the turbine. It will spin at max speed and produce max voltage but it doesn’t go anywhere.

As you start to draw current from the buck converter, it will in turn draw current from the generator which will provide resistance back on the turbine. The generator and turbine will slow down, producing less voltage, but it will be more than compensated by higher torque on the turbine and higher current through the generator, producing more power even though it is slower and lower voltage.

As you draw more and more current, the speed and voltage of the generator will decrease, and current will increase, giving more and more power, assuming the generator voltage remains above the output voltage so the buck converter can work.

It won’t go forever of course. There is some RPM of the turbine where speed * torque has a maximum value, and if you overload the circuit and the motor provides too much resistance, the speed can drop below this peak-power RPM and the turbine power starts to decrease.

You might get away with ignoring the overload possibility. I’m not sure what the best way would be to gracefully handle an excessive load…


I’m late to the conversation, but I would start by measuring the potential (vertical drop) and the flow. With both of those there is a lot of simple maths you can do to determine the maximum amount of power you will be able to generate, and match the generator accordingly.
Two things to keep in mind:

  • As implied above, you will want a turbine, not a water wheel. The former is much more efficient as long as there is sufficient flow.
  • You will want an AC alternator or motor, unless you only want to use some 12V lights a metre or two away from the power plant.
  • You will want a step-up transformer to turn 14VAC into ~240VAC. This will be sufficient for 10-100 metres.
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