# Measuring Power output of DC generator

• Deathz
Deathz said:
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.

Last edited:
berkeman
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

Deathz said:
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.

Baluncore said:
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.

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