Shorting coil gives back more power

[gyulasun]

Hi Joe,

Thanks for the video.  At the moment I have no clue why the sineswaves flatten with the shorting (I assume both FETs are in good shape).  Maybe you could use a second probe on Channel 2 of your scope to check the squarewaves controlling the common gates and sources, if you have not checked it?  (Ground clip goes to common negative of the 4421 and input clip goes to the gates.)

MAybe a series capacitor in the some uF (or higher) range is the clue for this, as shown in Doug Konzen schematic, see the 40uF cap labeled as 'high bypass filter' in series with the AC input leg of the full wave diode bridge: http://www.overunity.com/index.php?topic=10398.msg276614#msg276614   

Just wondering what is the FET type you use for switching?

Gyula

EDIT: be careful and do not connect the GND of CH1 probe to anywhere that has a different GND than the common negative of the 4421 when checking the gate-source drive signal.

ONE MORE Notice: in your photo showing the two Hall sensors above, both sensors are positioned at North poles. I ask one of the sensors should not be facing a South pole instead?

Hi Gyula and all others

I manage to record a short video of coil shorting. I tried many things but I always get flatten sine wave between the spikes.

http://www.youtube.com/watch?v=9V1Sgf9v6PA

....
Joe

[nul-points]

Hi Gyula and all others

I manage to record a short video of coil shorting. I tried many things but I always get flatten sine wave between the spikes.

Joe

hi Joe

impressive build - nice work!!


i have an idea about your flattened sine wave...

i think maybe either the control signal, or possibly the MOSFET polarities are inverted

it looks to me like your coil is shorted EXACTLY when you DON'T WANT it

of, course, this would mean the coil gets UN-shorted at the peaks - allowing a narrow section of the high part of the sine voltage to develop as usual - and being narrow it would look like a spike!

maybe you could check that your P & N-type MOSFETS are really connected where you think they are

and if they are ok, then check the voltage output from the control chip to make sure it's voltage is high or low at the correct point to switch the MOSFETS to short or un-short the coil


hope this makes sense - and helps!

all the best
np


http://docsfreelunch.blogspot.com

[Magluvin]

Hey Joe

I believe when the coil is shorted there can be no oscillation.
An inductor with current flowing when shorted, the current wants to continue. Only when the coil encounters a capacitance will it be able to reverse direction for oscillations or bemf. Its like a flywheel. Not exact, but current in a wire/inductors have inertial values.

Mags

[i_ron]

hi Joe


i think maybe either the control signal, or possibly the MOSFET polarities are inverted

it looks to me like your coil is shorted EXACTLY when you DON'T WANT it

of, course, this would mean the coil gets UN-shorted at the peaks - allowing a narrow section of the high part of the sine voltage to develop as usual - and being narrow it would look like a spike!

maybe you could check that your P & N-type MOSFETS are really connected where you think they are



hope this makes sense - and helps!

all the best
np


http://docsfreelunch.blogspot.com

Thats it!  I have to agree, good observation!

Ron

[gyulasun]

Hi nul-points,

Thanks for pointing out the obvious, unfortunately I could not see the forest from the tree.

One small correction to your post: the two MOSFETs are both N-channel types,  see schematic here: http://www.overunity.com/index.php?topic=10398.msg278867#msg278867  and they paralleled gate-source electrodes are controlled at the same time either on or off, and they switch between their separate drain-drain electrodes. When both FETs are off, their body diodes are in opposing series connection between their drains hence any AC or DC voltage polarity are blocked by one or the other diodes. (This opposite series connection of the drain-source path works because once the channel is opened it is able to conduct current into both directions.)

@Joe, as I suggested earlier, first use only one Hall sensor and check it to short only one of polarities of the sine wave peaks and when it is ok you can proceed to shorting the other polarity with another Hall.

Thanks,  Gyula