# Electricity Generator - variable kWh output, same mechanical power input?

#### humptydumptyaac

Joined Nov 3, 2021
24
Hi,

What would need to happen, to have an electricity generator produce varying amounts of electricity depending on how much electricity is needed, while the mechanical input stays the same?

Imagine a water wheel on which a force of 35 horse power acts continously.

The water wheel would then be able to produce up to around 20 kWh during peak requirement, for example in the evening at 8 PM, when most devices in the house are in use.

But what mechanism would it need to have, so it can also produce only 100 Watts, during the night when there's only a few LEDs for example, despite the mechanical input still being 35 HP, without any issues.

I was thinking of having a multi-planetary gear system, or a CVT continously variable transmission system, and some sort of chip/microcontroller that would switch gears depending on the amount of electricity needed, or a torque converter of sorts as I was once suggested here.

But I still haven't found a solution to that.

In other words, how to build an electricity generator that can produce 3 kWh when I'm running a 3kWh device, or 100 watts if I'm powering a light bulb, or 20 kWh if I'm powering all the devices I have, all the while the input mechanical power would be the same one needed to produce 20kWh.

Thank you.

#### Danko

Joined Nov 22, 2017
1,834
In other words, how to build an electricity generator that can produce 3 kWh when I'm running a 3kWh device, or 100 watts if I'm powering a light bulb, or 20 kWh if I'm powering all the devices I have, all the while the input mechanical power would be the same one needed to produce 20kWh.
Generator 20 kW without electrical load do not produces power, olny produce voltage!
With load 100W it will produce 100 W, with 3 kW load - 3kW, with 20 kW load - will produce 20 kW.
Power, produces by generator, equal power, consumes by load.
Converting a Watermill into a Hydroelectric Plant

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#### humptydumptyaac

Joined Nov 3, 2021
24
Generator 20 kW without electrical load do not produces power, olny produce voltage!
With load 100W it will produce 100 W, with 3 kW load - 3kW, with 20 kW load - will produce 20 kW.
Power, produced by generator, equal power, consumed by load.
Hmm.. I was under the impression that without load - the generator would continously produce 20 kWh and short circuit or something...

So in other words there is no need for a special mechanism? Only have a 20kW generator and it will produce as much power as it is needed?

#### BobTPH

Joined Jun 5, 2013
8,927
With no load, the wheel will spin fast, discharging the water at high velocity. The energy goes into heat from increased friction and kinetic energy of the discharged water.

With a load, the wheel will spin slower, reducing the energy lost to friction and to the water discharged.

Bob

#### humptydumptyaac

Joined Nov 3, 2021
24
With no load, the wheel will spin fast, discharging the water at high velocity. The energy goes into heat from increased friction and kinetic energy of the discharged water.

With a load, the wheel will spin slower, reducing the energy lost to friction and to the water discharged.

Bob
See, now that would be a problem for me. I'm trying to find a way by which the water would be discharged at the same rate, and also, understandably, I do not want the generator to overheat and cause problems of any kind without load.

What would be a way/mechanism in the generator, so that the outer wheel or propeller/archimedes screw would spin at the same rate, and discharge water at the same rate, while being able to produce different amounts of wattage?

#### BobTPH

Joined Jun 5, 2013
8,927
I think you are imagining a problem that isn’t. The generator will be hottest when producing max power.

Bob

#### ronsimpson

Joined Oct 7, 2019
3,037
Typically, there is a governor, that holds the speed of the water wheel constant. If the speed is too high the flow of water is decreased, if too slow the water flow is increased. Here is a picture of how this was done 100s of years ago.

Now you want constant water flow. Add to the pipe on the right, a "T" or "Y" at the top. Change the valve to a rudder that steers the water to the right or left. One pipe goes to the water wheel and the other goes around the wheel without adding power. Now the constant flow of water will be divided into two flows of variable flow.

At no load it will take very little water to turn the wheel. At full load it will take all the water to turn the shaft.

#### ronsimpson

Joined Oct 7, 2019
3,037
I looked at my generator for a tractor. It wants a constant 450rpm to get 60hz. If the rpm changes the 60hz changes. Can be set to 50hz or 55 by changing the speed on the shaft.

There is a regulator inside the generator that feeds power to a control winding. The output voltage is controlled by current in the control winding. So if the rpms are not right (or the load changes) the generator will still make the right voltage. (with in reason)

The tractor has a governor that can be set to 450rmps. The amount of gas burned changes to hold the rpm constant. With no load there is very little gas burned. At 50,000 watts the motor is producing black smoke and working very hard.

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#### crutschow

Joined Mar 14, 2008
34,392
If the generator is producing AC, then you will need a governor, as ron stated, to regulate the water flow and keep the generator RPM constant.

#### GetDeviceInfo

Joined Jun 7, 2009
2,194
Yes, regulation is likely best obtained via excitation of the generator. Adding a storage element would allow higher peak draw. AC inverter would keep output clean.