STEORN DEMO LIVE & STREAM in Dublin, December 15th, 10 AM

[hartiberlin]

Hi Ben,
could you please post the value of the ohmical resistance of your coil
(just measure via a multimeter with the OHM settings)
and a zoomed in scope shot of the input current into your coil,
where one can see the rising current waveform from zero amps to just the
maximum input current over maybe 8 divs in the horizontal direction
and please state milliseconds/div.


Then we can calculate the L of your coil
and also the tau timeconstant and can optimize the supply voltage and Ontime
for maximum BackEMF power recovery.

Many thanks.

Regards, Stefan.

[hartiberlin]

Hi Ben,
was the first picture DSC04415.JPG of your
posting in:
http://www.overunity.com/index.php?topic=8411.msg217358#msg217358
the timebase set to 5 millisec/div or was it set to 5 microseconds/div ?

If it was set to
5 millisec/div
the tau=L/R is about 0.5 millisec,
so if we would know the ohmical resistance of the coil,
we could calculate L= tau/R

Then you need to use a much higher DC supply voltage to only
switch on for about 0.1 Milliseconds( 1/5th tau) to  reach the same input current
level as you used now after about 2 Milliseconds.

[hartiberlin]

Okay Ben,
let´s calculate some more:

From:
http://www.overunity.com/index.php?topic=8411.msg217358#msg217358

I can see, that you used a 10:1 divider scope head, as the
voltage in the upper trace is about 8.5 milliVolts at a 0.1 Ohm shunt
maximal input current amplitude pulse.

So it was 12.4 Volts DC input at maximum 0.85 amps then,
that gives a DC resistance of about 14.5 Ohms for the coil.

Could you please verify this with a multimeter ?
Many thanks.

As tau=L/R is the time the waveform reaches about 63 % of the maximum amplitude
it is about 0.5 Milliseconds in your scope shot. ( a higher horizontal res scope shot would help)

So we can calculate now L of your toroidal coil:

L= tau/R= 0.0005 sec / 14.5 Ohms = about 34 microHenries

So now we can calculate what amount the coil L can store maximum
of magnetic field energy when it is energized by
0.85 amps in your example:

W= 0.5 x L x I^2

So we have 0.5 x 0.000034 H x (0.85 amps)^2= 12.3 microWattsseconds

So you see the coil has much too low Henries to store enough energy
for better BackEMF recovery.

Would be good, if the coil would at least have a few hundred MilliHenries.

Regards, Stefan.

[hartiberlin]

Okay, now we can calculate, what the supply voltage would need
to be, if we want to have the current level of 0.85 amps already
at 0.1 milliseconds.

As the current waveform function i(t) is:

i(t)= Vsupply / Rcoil x ( 1 - (e ^t/tau) )

we can solve this for Vsupply( supply voltage)

so we can rewrite this as:

with i(t)= 0.85 amps
with    t= 0.1 millisec
with tau= 0.5 millisec

Vsupply= 0.85 amps x 14.5 ohms / 0.18127 = about 68 Volts

So Ben,
if you would raise your Supply Voltage to 68 Volts and switch on your toroidal coil
just for 0.1 Milliseconds ,
you could extract about 90 % of your inputed power back
into your cap.

Regards, Stefan.

[k4zep]

Hi Ben,
could you please post the value of the ohmical resistance of your coil
(just measure via a multimeter with the OHM settings)
and a zoomed in scope shot of the input current into your coil,
where one can see the rising current waveform from zero amps to just the
maximum input current over maybe 8 divs in the horizontal direction
and please state milliseconds/div.


Then we can calculate the L of your coil
and also the tau timeconstant and can optimize the supply voltage and Ontime
for maximum BackEMF power recovery.

Many thanks.

Regards, Stefan.

Hi Stefan,

From orginal measurements when building coil, each segment is 3.15 ohms for a total of 12.6 ohms series resistance , Each coil is 567 uH as wound and when is wired as shown has a residue of 16 uH inductance.  I did not try to balance coils by trimming windings.

Have found by experimentation that coil can run very close to magnets and while it cogs like heck, with power it runs like heck.  Also I put Hall Effect directly between coil and passing magnet for precise trigger on that individual magnet/core interface.  Runs about 800 rpm now @ 3.15 watts @ 12.6 VDC.  Mechanical limitations of my simple rotor are starting to be a problem.  Need to build a new motor. I need to add a pulse modulator where I get the same width pulse for each magnet and have the ability to narrow the width down for optimization but that is further down the track. Possibly an optical pulse interface would be more advantageous later on down the road.   It is obvious with correct number of coils, interfaced on the face of the toroid and not the side that a much more powerful motor could be built and at much lower power input.

Respectfully,
Ben