Electromagnet Question

[mondrasek]

I put a 1.6 Ohm resistor in series with the solenoid per Gyula to read the votage drop across it as an indirect way of measuring current in the solenoid circuit.  I'm not really interested in the absolute values, just the difference in the current over time as the permanent magnet is accelerated away from it's starting position inside the solenoid.  Again, I did not see the results I expected.

Without the permanent magnet inside the solenoid the voltage measured across the solenoid and the in-line resistor both rise to their steady state values and hold when I press the switch connecting them to the 9V battery.  The o-scope traces look exactly like a square wave.

With the permanent magnet inside the solenoid the voltage measured across the solenoid and the in-line resistor both rise to the same values initially.  But the voltage across the in-line resistor then drops slightly before returning back to the expected steady state value.  The shape of the curve of this voltage drop and it's return to normal appears to be a nice parabola.  I assume the drop in the voltage curve represents is the permanent magnet accelerating and the return icurve representss the two magnetic cores increasing in distance.

So does this mean the current to the solenoid actually decreased as the permanent magnet was accelerated away?  Did the power consumed by the solenoid actually decrease as it did work upon the permanent magnet?  Or where (oh where) is the measurment error now?

Thanks,

M.

[triffid]

test

[mscoffman]

@modrasek;

If that is what you measure then that is probably it. One thing to think about is the
fact that the magnet has two poles and what does the solenoid see as it accelerates
the magnet through itself. It could be that the solenoid's stronger field actually forms
lenz current in the magnet. That bounce could also be from the power supply recovering.
See a better method below.

So if you see a decrease in current it maybe true. Don't forget that energy is measured
in "milliwatt seconds" and time plays a factor, if you have to keep the solenoid energised
longer to fire the magnet and increase the field then it has potentially used more total
energy.

IMHO you will not see overunity when an electromagnet accelerates a magnet. You will
see overunity if one PM lifts another. (but then lose momentum of the wheel trying to
pull them away from one another). There is also Smot runner gain, but one hasn't (yet)
extricated the runner to get it to the beginning of the track array.


@ALL

If you want to see overunity energy production from the Bedini
Fan I recommend use of acid/lead storage batteries or Gel Cells
for both the source and the charging battery as the overunity
part occurs due to battery chemistry. Don't use strange battery
chemistry ..and then say that the overunity part doesn't work,
please.

Small Acid/Lead Batteries are available in those automotive jump-start
units and small grey or orange Gel Cells are available in building
emergency lights that come on when the utility power fails. I like
the small batteries used in ICE motorcycles. They also make 9Volt
size acid/lead's I believe. 9volt batteries are probably too
small to support the fan well but it's worth a try.   

imhotep's Bedini Fan is an excellent experimental device as it doesn't
have an electrical interference footprint much larger then a normal
DC fan. imhotep's Morray's Vibrator Overunity Light unit also is
an excellently simple device, some experimentation will be required
to modify the base unit for other applications however. See
imhotep's youtube.com videos for more details on building these devices.
A Bedini Fan might be a valid manufactured product...overunity included!
Rather then build a Bedini SGS motor which I don't consider a good
experiment why not include *your own* electrically run wheel motor as
an actuator in a custom version of a Morray's Vibrator circuit?

imhotep's videos:

http://www.youtube.com/user/kojsza


The principal being demonstrated;

http://uk.youtube.com/watch?v=qaCk0jK--8s


----

Magnetic Pulse Experiment

The following experiment should let one see then pulse from a magnet
in a straw accelerating away from being fired by a solenoid coil when
you apply power through a switch. This isn't easy to do experiment but
here goes;

Remember that a capacitors store power proportional to it's voltage
while inductors store power proportional it's current. So it is
easier to think about inductor equations in terms of current.

What we are going to do is look at the current flowing through
two coils simultaneously and use one coil as reference and
subtract that from the coil that accelerates the magnet using
functions available on most oscilloscopes. The "invert" and "add"
channels functions.

a) you need;
   two identical solenoid coils and if you don't have scope current
   probes we can use two "current transformers" instead. (see Wikipedia)

http://en.wikipedia.org/wiki/Current_transformer

   A valid current transformer is a 20KHz bandwidth audio transformer
   line-to-load transformer with a 600 ohm impedance primary
   (audio line = 600ohms) and a 1.6 ohm secondary or the lower
   the better. I would say 100Watt audio transformer
   (audio bandwidth = 0->20KH) you then must solder a 600 ohm 5watt
   resistor across the 600 ohm primary or match the primary resistance
   in a way that is won't accidentally disconnect else a current
   transformer can become a shock hazard and damage equipment. Now
   connect the low resistance secondary(s) in series with coil(s)+power
   supply and attach one each primary+resistor to each of two scope voltage
   channels.

b) now flip the "invert" switch on the reference scope channel

c) find the "add" channels button on the scope

d) the "invert"+"add" now equals "subtract" one channel signal from
   the other

e) now one has to adjust the gain of the channels so that the pulse
   visible then the power supply is "fired" into the two solenoids
   then adjust the channels so that the difference is as small as
   possible when there is nothing fired from both solenoids.

f) You can validate that swapping the straw and magnet between
   solenoids should create a plus going pulse when the magnet
   is in one and a minus going pulse when it is the other.
   The magnet uses most energy at the beginning to accelerate
   therefore the pulse.

g) you can also watch as a magnet flies-by with an some other inductive
   coil attached to the scope. There will be a bidirectional pulse
   at the moment the magnet flies past, with the zero transition
   at the point of closest approach. The Bedini Motor 2n3055 transistor
   circuit uses a sense coil that works this way.


:S:MarkSCoffman

[gyulasun]

.... The o-scope traces look exactly like a square wave.   

Hi Mondrasek,

It seems like a square wave first but if you change a little on the timebase of the scope then you can see a typical exponential voltage (i.e. current) curve every inductance produces.  See this link where you can find a series LR circuit with typical current-voltage curves in the function of time. Notice that the value of R in Figure 2-10A  includes the DC copper resistance (if I recall it 75 Ohm in your case) plus your 1.6 Ohm series inserted resistance too. Here is the link:
http://www.tpub.com/neets/book2/2c.htm

Try to reach similar scope pictures on your scope like in Fig. 2-10B  and then you may proceed to the tests with the inserted magnet, ok? 

Edit: I just noticed that on the next page of the link there is the typical exponential curnet curve shown in Fig.2-11 here: http://www.tpub.com/neets/book2/2d.htm   

With the permanent magnet inside the solenoid the voltage measured across the solenoid and the in-line resistor both rise to the same values initially.  But the voltage across the in-line resistor then drops slightly before returning back to the expected steady state value.  The shape of the curve of this voltage drop and it's return to normal appears to be a nice parabola.  I assume the drop in the voltage curve represents is the permanent magnet accelerating and the return curve represents the two magnetic cores increasing in distance.
So does this mean the current to the solenoid actually decreased as the permanent magnet was accelerated away?  Did the power consumed by the solenoid actually decrease as it did work upon the permanent magnet?  Or where (oh where) is the measurment error now?

When the magnets starts moving up, it obviously starts inducing current in the coil and if you see the current reducing parabolically during this time it should mean the current consumption for these moments also reduces. Interesting. Maybe the position of the magnet where it starts kicking out from the coil influences the current reducement? would stand to reason.  It would be interesting to see the shape of the curve in the same time base scope set where you already can nicely see the coil exponential current curve without the magnet.

rgds,  Gyula

[mondrasek]

@mscoffman.  Great information as always.

@Gyula.  I was able to see the correct exponential curve when adjusting the timebase as you suggested.  Unfortuantely I was working with another unfamiliar o-scope since the one I had played with earlier was out in the field with a technician doing actual work (not my desk experiments).  This new scope was taking too much time to learn and the only way to see the current drop due to the magnet on screen was to change the timescale so that the exponential curve was compressed to look like the square wave.

I was very interested by the current drop, but as mscoffman says, this drop is over a much longer time period than I would have expected compared to the saturation rate of the circuit.  Interesting effect, but what could it be good for?

I was curious if I could keep the circuit/solenoid charged only as long as the current drop was occuring.  In a failed attempt I replaced my mechanical switch with a custom design, utilizing the perminant magnet as a switch contact.  I placed the two wires oringally connected to the switch into the bottom of the tube supported by other elements so that they were contacts that would be bridged by the permanent magnet.  With this in place I then was able to move the solenoid up and down the straw to different locations with respect to the permanent magnet, into repelling and attracting, up and down configuarations.  When the solenoid pushed or pulled the magnet upwards it would break the circuit and allow the magnet to fall again, re-connecting the current.  The result was interesting at best.  The resultant pulses of current applied to the solenoid would only raise the magnet a less than noticable amount, though you could hear and see the vibration and arcing.  So the switching frequency was fairly high.  Putting the multimeter across the solenoid in AC mode caused readings from several hundred milliVolts to several Volts above the DC supply Voltage.  I'm not sure if that was due to the moving permanent magnet, the BEMF, or both.  But it was interesting all the same.  I'd like to see a similar setup that allowed the solenoid to to be energized for longer.  I don't see this as being easily possible with a mechanical set up and instead would require a variable rate switching circuit.  Again, I'm not sure what this would accomplish, but now I'm just playing while trying to think where the current drop effect could possibly be useful.

Thanks again to everyone for all the info and ideas.

M.