UFO politics Keeps his word 12-12 12 Let the games begin.......

[MileHigh]

TK:

Voltage is the "pressure" that pushes charge through an impedance. Current is the time rate of flow of charge. Could you tell me the difference between a "voltage source" and a "current source"?

I can give you a pure technical answer but it probably won't mean too much for the guys on the EF thread.  An ideal voltage source has an output impedance of zero, and a real voltage source has an output impedance close to zero.  An ideal current source has an output impedance of infinity and a real current source has a very high output impedance.

Here is a simple thought experiment to explain the very high output impedance of a current source:  Imagine you have a 100-million-volt voltage source in series with a 100 mega-ohm resistor.  Suppose you try putting different resistances across the output of this device.  100-ohm, 1k-ohm, 10K-ohm,  100k-ohm.  What will the current flow be in each of those cases?  How much power will be dissipated in the different resistances?  Assume that this thought-experiment current source has two terminals that are separated by 2 centimeters.  What happens if you put a short-circuit across these two terminals?  What happens if you open-circuit these two terminals?

With respect to your bench power supply, you probably have a few with the 10-turn knob for the voltage setting and the 10-turn knob for the current setting.  You explained how you can play with the current setting to do current limiting.  However, you can use your power supply to act as a voltage source or as a current source.

For voltage source mode, it's pretty straightforward.  You turn the current setting all the way up to the maximum, and then you simply adjust the voltage setting to your desired voltage.

For current source mode, it's similar but used much less often.  With the current setting at zero, first turn the voltage setting all the way up to maximum.  Then connect the two leads from the power supply to the circuit under test.  Then turn up the current setting to your desired current level.  Now as you change your circuit your power supply will always inject the same amount of current into the circuit.  This can be a very useful function when designing and debugging circuits.

A discharging coil is basically a current source.  In fact it's very close to an ideal current source.  Hence people observe voltage spikes and plasma arcs and mistakenly call that "cold electricity."

Going back to the DC motor being powered by a current source, if you put a big mechanical load on the motor and it slows down, you know that you are lowering the electrical impedance of the motor relative to the current source.   The slower a motor turns the less counter-EMF it is generating hence the lower the electrical impedance of the motor.  The lower the impedance a current source sees the less power it outputs.  That's in contrast to a voltage source where the lower the impedance it sees the more power it outputs.

There was a clip recently discussed where the experimenter puts a load on the motor shaft with two wooden blocks and the motor slows down.  Because the motor was powered by a current source it slowed down in a "benign" way and drew less and less power and came to a stop.  The problem is that a motor is not supposed to do this - it's supposed to "fight" and draw more power when you put a load on it.  The motor needs to be powered by a voltage source to do this.

MileHigh

[fritz]

My bench power supply has a current-limiting mode. You short together the output leads and set the current limiting pot to the desired short-circuit limiting current. Then the power supply regulates its _voltage_ to avoid exceeding the limiting current when the load's impedance drops.

A constant-current supply will vary its output voltage as the load's impedance changes, in order to maintain a constant current in the load.

It´s quite usually to optimize voltage sources with bypass capacitors - but there are few people improving their current limiting voltage sources(==current sources) with 1Henry coils.
A current limiting voltage source is a poor substitute for a true current source.

[MileHigh]

Torque Test One:

http://www.youtube.com/watch?v=bvgoRRfgbA0&feature=youtu.be

UFO has a really nice setup.  Unfortunately he makes a big mistake.  Who will be the second person to point it out?

His asymmetrically modified imperial motor is under unity.  I am somewhat surprised in that it seems to be about as efficient as you would expect an unmodified motor to be.  However, this was just one test and the real way to compare the modified vs. unmodified motors would be to plot performance curves for both of them and compare.

Some comments from UFO:

The Scales are around 1.5 to 2.0 % error
Meters are not "cheap ones" but True RMS Both
The only thing here I am not satisfy with...is with the DC Clamp Meter...which is designed to measure Linear DC and NOT Pulsed.
And all my Motors are pulsed In and Out:)
Pulsed DC should read much less Amperage than what is showing linear reading with that Clamp.

I seriously doubt that his DC clamp meter is wrong.  Note also that the three batteries are directly connected to the motor.  So when he says "pulsing" he is talking about the current draw by the motor itself, and not some sort of external pulsing circuitry.


The only thing that may be a bit off in one or two of his measurements is that he may have frozen a frame when the motor was decelerating.  That will completely muck up the measurements.  The motor absolutely must be turning at a constant velocity when you gather data points.  In a related matter I get the impression that he was applying force to the lever with his arm to create the friction for the Prony brake.  That's okay for a first test but to be serious he needs to add some weights to the lever so that he takes the human factor out of the equation for creating the friction.

Also, you have to look at the digital displays for several seconds while the motor is turning at a constant velocity and make sure that you are recording the "real" reading and not the occasional reading that is above or below the "real" reading.  We are all familiar with how digital displays can jump around.  I am not sure if UFO was paying attention to this when he froze the video frames.

These two points about the art of making proper measurements are very critical and can never be ignored.

MileHigh

[ramset]

This UFO is one hard working fellow.......

TORQUE_TEST_ONE - YouTube

Thx
Chet

[Nickstir]

UFOPolitics video on the torque test is based on Peter Lindemann's -- Electric Motor Secrets. Peter's video can be seen here:

http://www.youtube.com/watch?v=iLGuf1geOiQ

The first 13 minutes of Peter's video should give you an idea of what UFO is trying to do. UFO has mentioned in the past that he uses Lindemann's -- Electric Motor Secrets like a 'bible'.

Nickstir