Study of Generator Coil Acceleration Under Load (moderated)

[wattsup]

@gotoluc

As usual good work in trying to define that effect. I made a post but forgot to post it before I left for the office, so I will make this quick.

The metglass lams are placed horizontal in your set-up and the rotating magnet is also horizontal but smack dab aligned to the center of the metglass. What I think is happening is the center 3rd of the metglass icore which is closest to the magnet passage is getting all the impress leaving very little to the top and bottom 3rds which are the ones the coil will see and react to as change. Maybe realign the magnet so its closest point is aligned with the top or bottom 3rd and try your test again. See if the metglass now does the same as the rod.

Thanks for your works man.

Added: I forgot to also mention this.

You did not talk about that vertical pancake coil next to the magnet. It is also probably affecting the metglass as an impress brake more then it does on the regular rod, so maybe try connecting and disconnecting that coil as well.

wattsup

[gotoluc]

@gotoluc

As usual good work in trying to define that effect. I made a post but forgot to post it before I left for the office, so I will make this quick.

The metglass lams are placed horizontal in your set-up and the rotating magnet is also horizontal but smack dab aligned to the center of the metglass. What I think is happening is the center 3rd of the metglass icore which is closest to the magnet passage is getting all the impress leaving very little to the top and bottom 3rds which are the ones the coil will see and react to as change. Maybe realign the magnet so its closest point is aligned with the top or bottom 3rd and try your test again. See if the metglass now does the same as the rod.

Thanks for your works man.

Added: I forgot to also mention this.

You did not talk about that vertical pancake coil next to the magnet. It is also probably affecting the metglass as an impress brake more then it does on the regular rod, so maybe try connecting and disconnecting that coil as well.

wattsup

Hi wattsup,

it makes no difference to the effect if I raise or lower the rod in relation to the center of the magnet rotor.

Luc

[MileHigh]

Well, I am baffled because the clip shows that the "effect" is exactly what I said it was.  It has nothing to do with the choice of core material and everything to do with the magnitude of the mechanical load on the prime mover.  In this experiment all that you have to do is measure the electrical load due to the coils and load resistors and that becomes the mechanical load on the prime mover.   Eddy current losses and hysteresis losses also simply become more of a mechanical load on the prime mover and also act to slow it down.

Starting at about 20:00 minutes into the clip you have the most dramatic "acceleration under load" when the 10-ohm resistor gets changed to the 1-ohm resistor.  Luc even acknowledges that the electrical load decreases when he does this.

With the 10-ohm resistor, the total electrical load is about 1.58 watts.

Then the load resistor is changed to 1-ohm, the prime mover speeds up, and the total electrical load is about 0.98 watts.

So, "acceleration under load" is really "acceleration (to a higher final RPM) under reduced load."  In that sense there is no "effect."

[verpies]

Okay everyone, I made the video as promised...
Link to the movie: https://www.youtube.com/watch?v=NYGM4UlnqTM

Good video!  I agree with your experimental methodology and manner of analysis and reasoning.

I see a mathematical mistake in it though.

There are several 2-variable formulas for calculating average power, such as:
P=V*i
P=V²/R
P=R*i²
...and there seems to be confusion when to use an RMS value and when to use the arithmetical MEAN value, in these formulas.

The distinction is very simple: 
- If you see a squared current or voltage in the formula, then you should use the RMS value for it.
- If you see a non-squared current or voltage in the formula, then you should use the MEAN value for it.

IMPORTANT: In the formulas above, only one variable can vary in time and the second variable must be constant (it cannot vary in time). 
If both variables vary in time, then you must use an oscilloscope and its MATH function to calculate power one instance at a time, by multiplying 2 channels and averaging the results, unless the current and voltage have exactly the same shape and you know their exact phase offset.

According to the rules above, it was perfectly fine to use the RMS voltage in the formula P=V²/R  to calculate the average power dissipated in a 10Ω resistor, because its resistance was constant (10Ω) while the voltage across it was variable and squared in the formula.

But it was not OK to use the RMS current to calculate the power supplied to the "JobMate" motor according to the formula P=V*i  although the supply voltage was constant at 28VDC, because the current in this formula was not squared .


P.S.
Some multimeters are capable of calculating the RMS values of non-sinusoidal waveforms ...up to a certain frequency.
e.g. my Fluke 87 can do it and I just recently verified it on a 330Hz sawtooth waveform.

[verpies]

You did not talk about that vertical pancake coil next to the magnet. It is also probably affecting the metglass as an impress brake more then it does on the regular rod, so maybe try connecting and disconnecting that coil as well.

That coil does not exert any influence on the rotor because no significant current is allowed to flow through it.
A coil without current might not as well exist at all.