Measuring Power output of DC generator

[Deathz]

Yes, but there is friction and leakage in the screw turbine.


For maximum power output, you will need to load the generator until the voltage falls to 2.35 volts. Another way is to measure the internal resistance of the motor when it is not turning, then load it with that resistance.

Okay, once the voltage decreases, the current also increases right? So it is important to have a constant RPM between different load?

 

[Deathz]

If I am going to compare the efficiency of the two? What should be the constant parameter sir? Is it okay if i will base on the flow rate?

 

[Baluncore]

Can I use a resistor as a load?

Yes. You will need to adjust the load, and it will need to dissipate the power generated.

But if I will use a higher resistance load to get the voltage into half, the turbine will stop rotating.

It will slow down, but it will not stop.
If it stops, the voltage will be zero, not half.

If you want to compare the efficiency of the original and modified generators, you should run them at a specified RPM, from some standard motor, not from an Archimedes turbine with unknown flow, leakage and friction parameters.

 

[Deathz]

Yes. You will need to adjust the load, and it will need to dissipate the power generated.

It will slow down, but it will not stop.
If it stops, the voltage will be zero, not half.

If you want to compare the efficiency of the original and modified generators, you should run them at a specified RPM, from some standard motor, not from an Archimedes turbine with unknown flow, leakage and friction parameters.

If I'm not using Archimedes as a reference, how can I determine the power input based on the input RPM?

 

[Deathz]

Like for example, I will use a drill in order to control na Input RPM, how should I compute the power input?

 

[Rive]

What specific load should I use to ensure at least one centiampere to achieve a bigger power output?

Usually you need an MPPT controller/charger to maximize the power from such setups, and that could either dump the power directly to a battery of fitting size and measure it.

I don't know whether MPPT of such low voltage/power exists, so this might be a project to be delegated to some basic uC controlled circuitry.
There might be already related/applicable projects in Arduino or similar communities.

 

[Tom.G]

The easiest way to find the maximum output power is to measure the voltage, current, and resistance while changing the load.

You can change the load with a variable resistor, then document the voltage and current at various settings.

This search turns up several appropriate variable resistors:
https://www.google.com/search?hl=en&q=5+ohm+10+watt+potentiometer

Have Fun! (and please let us know what your results are)
Tom

 

[Baluncore]

Like for example, I will use a drill in order to control na Input RPM, how should I compute the power input?

Power is the product of torque and RPM. So you measure the RPM and the torque of the driving motor. Convert the RPM to angular velocity in radians per second, then multiply by torque in kg⋅m, to get watts.

The torque can be measured by attaching the motor to an arm that rotates freely about the same axis as the motor or generator. Use digital scales to measure the force on the arm. Compute the driving motor torque from the length of the arm and the weight.

 

[Deathz]

A stronger magnet will induce a greater voltage, but I wonder how well it fits mechanically. There may be a bigger air gap in the magnetic path that could limit the power.
Is there only one magnet ?
Did you check the pole pattern before fitting it ?
How similar were the dimensions?


That should give an increase in voltage of 36/30 = 1.2 times.


The picture you posted shows an auger (blue) in a semi-cylindrical housing (black). There will be problems with friction, or the seal leakage, between the auger and the outer tube. That may be one cause of low efficiency.

An Archimedes screw could have the helix attached to the outer tube, so the outer tube then rotates with the helix, so there is no leakage, and no seal friction. An Archimedes screw can also be made from a spiral of pipe without any seals.
Google search, images; Archimedes screw

How should I compute the efficiency?

Is this correct?
% = YgQh/Pout

Where Pout = Voltage x current
Y=density
G=gravity
h=head
Q= flow rate


Note: I don't need to have a high efficiency of the turbine. What I need is the efficiency of the generator itself.

How do I calculate the electrical efficiency of the generator. The generator only produces 6 watts while when I computed the power that the water can produced is 227 watts.

Do I need to compute the efficiency of the Archimedes and the head loss? which makes the formula for the power input to be
P=ygQHxefficiency ???

The power that the water can produced is 227 watts but I think it is not the overall power that it can give to the generator because of the losses and the efficiency of the screw.