I have a 5000 watt, 3600 rpm 60 hz generator.I plan to connect it to a 1500 watt baseboard heater. Assuming the water wheel can supply sufficient power to the generator, how will water wheel rpm affect power output? In other words if I supply all the power it needs to the generator, but the generator runs at say 500 rpm can I still in theory get full power from it or do I have to gear up 3600 rpm? I am planning to run one or more electric baseboards only

  • \$\begingroup\$ Your first question should be “how much power is available in the water”? Ie how much flow and head have you got to work with? As for rpm it will need to be controlled as if you want 60hz +\- x then the water wheel speed with the gearing makes a difference. \$\endgroup\$ – Solar Mike Feb 10 at 19:08
  • \$\begingroup\$ Read up on how synchronous generators work. Other than that Solar Mike has the right idea; you need to worry about how much energy you can get from the water. If the river conditions are fairly stable, you can just use a fixed gearing, but if they vary wildly with weather as many rivers do, you may need something more advanced. I've never worked with waterwheels before, but I'd imagine something to control the water flow before reaching the wheel is the best way to do that. \$\endgroup\$ – Hearth Feb 10 at 19:15
  • \$\begingroup\$ We are only assuming it's a synchronous generator (although it's a pretty good assumption given that it's 3600RPM and 60Hz). Henk -- please edit your question with a link to the generator data sheet, or if it's an old salvaged thing, get a picture of the nameplate and (if there is one) the connection panel. \$\endgroup\$ – TimWescott Feb 10 at 19:18
  • \$\begingroup\$ Heating only? Or have you other uses for the produced electricity? If you are early enough (=no heating still assembled nor purchased) you have a possiblity to consider, if you could produce the heat with a brake. It can be simpler, if the needed transmission distance is short. Commercial water brakes exist. \$\endgroup\$ – user287001 Feb 10 at 19:18
  • \$\begingroup\$ Just noticed one thing: You write like the generator could decide how many watts it outputs. You asked in one comment if the generator can make 1000W as 50V and 20A? Hopefully you know ohms law. Generator produces certain voltage and the resistance of the load defines how much current it will take with that input voltage. Then one can calculate the power as U*I. Generator cannot at first decide its output voltage and then force the load take a certain current independently on the voltage. \$\endgroup\$ – user287001 Feb 11 at 22:45

So, briefly and you can research detailed information about water wheels and electricity generation.

Power = Q (flow in L/s) * g (gravity) * H (height) * efficiency

Gravity can be assumed as 10 due to the inaccuracies - because none of the other items will be precise...

High head tends towards Pelton wheel installations while Low head high flow are Kaplan turbines. There are several different turbines available and Pelton for example can have a single or multiple jets...

Any installation will need intake valve control and usually a surge pipe to deal with rapid intake valve closing and dissipating the inertial forces...

There are lots of other things to be considered, one of the most important is having permission to extract the water from the source and also to put it back into the source after it has been through the turbine. For that you will need to contact the relevant authority.

There are, in many countries, people who specialize in this sort of thing, try looking under renewable energy and check out those who have successful installations...

  • \$\begingroup\$ I spent some time studying the generation of energy from water, since I was considering the purchase of land that included a lake and water rights (dating to 1902) to the river that passed next to it. This situation was a low-head case and I learned a lot by examining various designs. You went straight into this with the right names for the OP to look up and immediately divided the problem up into the two basic situations. +1 \$\endgroup\$ – jonk Feb 10 at 20:17

The voltage and frequency that the generator will produce will be proportional to speed. At 1800 RPM, you will get 30 Hz and about half of the voltage that it is designed to produce at 3600 RPM. The required torque to get the rated power will be about 10 pounds-feet or about 13.6 Newton-meters. You will need the same torque to get half of rated power at half-speed.

  • \$\begingroup\$ So, in water terms 50m head, 20 l/s and assuming 50% efficiency should do it... \$\endgroup\$ – Solar Mike Feb 10 at 20:30
  • \$\begingroup\$ @Solar Mike: How does that comment relate to my answer? \$\endgroup\$ – Charles Cowie Feb 10 at 20:45
  • \$\begingroup\$ Where do you think you will get the torque from? \$\endgroup\$ – Solar Mike Feb 10 at 20:46
  • 1
    \$\begingroup\$ It is not for me to say where the torque is coming from. The OP only asked "Assuming the water wheel can supply sufficient power to the generator, how will water wheel rpm affect power output?" \$\endgroup\$ – Charles Cowie Feb 10 at 20:49
  • \$\begingroup\$ So the title doesn't give you an idea then? ie Water wheel power generation .... \$\endgroup\$ – Solar Mike Feb 10 at 20:51

I bet after the electricity exists, it would be nice to use it for other purposes, too. Then it must have the right voltage and frequency. A small amount of an unstable output of course could be converted electronically to perfect mains AC with minimal cost.

This is not a trivial engineering task for a hobbyist. A pro wouldn't ask. As commented you must have some data of the available water flow to decide what mechanical turbine would provide the needed torque and rpm. Then you must decide how to control it. You must control the input water like you would control a gasoline engine. A synchronous generator in addition must have magetization control system. A massive flywheel is possible in fixed installations to remove the need of fast actions.

Unfortunately without knowing your generator the water, terrain nor climate conditions I cannot write better. But one thing is sure. You must have a local waterfall - maybe inside of your system, but it must exist. Nothing else generates the power. You seemingly already have got other answers of it.

ADD A comment suggests that you would be satisfied with some power, far below the max capacity of the generator and maybe at sub-normal frequency. But you do not know would the generator make it; I assume you plan to have a sturdy waterwheel + simple gearing which rotates the generator well below the nominal speed, but generates surely all the needed torque to keep it rotating under the load.

I don't know your generator. DC generator (you haven't it) or synchronous AC generator with properly controlled magnetization circuit can work as you hope.

But your unit can be the common asynchronous one with cage rotor. It's basically a 2- or 3-phase motor which is rotated faster than the nominal synced speed to turn it to generator mode.

Connection to AC grid is replaced by an oscillating resonant circuit (=dummy reactive circuit in parallel with the actual load). Often adding capacitors are enough due the inductance of the motor windings. Rotation must happen with a slightly bigger rpm than the resonant rpm. Otherwise you get nothing, the output simply stops totally if you cannot keep the rotation speed in certain limits which is defined by the properties of your generator and the extra reactive load. Sub-60Hz can be possible with proper reactive load, but the resonance can vanish if there's not enough inductive reactance. You cannot compensate it by making only capacitors bigger.

If the theory of asynchronous generators is interesting, start by searching for "induction generator" That's the popular alternative name for it.


  • electronic parts in your heating system (=something more than mechanical thermostats) can require proper mains AC supply voltage.
  • do not assume your insurances are valid if you design or build (or both) fixed electric installations without having proper certificates. In certain countries where the state patronizes everything, you can in addition get hefty fines if everything isn't circulated properly through the right bureaus.
  • \$\begingroup\$ with high torque and low rpm will I still get usable power out of the generator, ei could I have a 1000 watt at for example 50 v and 20 amp? \$\endgroup\$ – Henk Hengeveld Feb 10 at 23:24

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