Hendershot Replications

[mlurye]

I tried many "door bells", "PHONE BELLS" "fire bells", etc... with many different voltages (AC/DC, with or without included magnet...).
I've noticed that high voltage bells always have high resistance (it seems obvious I know).
The only bell made for 110V I found has unfortunately a single coil... I measured 1370 Ohms and 1.15 H and the wire is very very thin... Too thin I guess. I heard that "antique" 110V railway station bells are made with two coils and I try to find one on EBAY...

Concerning the 7.8 nF capacitor, i made some experiments with home made, using garbage bag polyethylene film (not easy to make, too). I had some results but I wonder if the only important thing would be the difference between the two tanks capacitors. This is not a new idea, I know... but I can't find out what action the coils could have on capacitors. This is beyond my knowledge and imagination. If somebody knows....

Here is good one 2 VTG DOORBELL YARD BELL #641 - eBay (item 390106534943 end time Oct-25-09 18:05:33 PDT). I would get it myself, but I'm going on vacation for 2 weeks.
I'll give you my imagination about coil/capacitor. It was tuned to the local AM (~520KHz) radiostation. And it was building potential difference on a cap ...
The rest is not clear yet, but I'm thinking about it

[mlurye]

morpher,
what did you use as a base cylinder for your capacitor?

[morpher44]

Lenz's Law

but I can't find out what action the coils could have on capacitors. This is beyond my knowledge and imagination. If somebody knows....

@NOMDI

Lenz's Law!!!

Take a neodymium cylinder magnet and drop it down a copper pipe
with a diameter slightly larger than the neo.

Notice that it doesn't fall at 9.8 meters/sec*sec

Rather it slowly floats down and arrives out the other side
-- as if traveling in slow motion.

The eddy currents established in the copper due to induction
hold the magnet and resist its decent.

So, now lets instead wrap a COIL of wire around a copper cylinder
and pump AC currents through the coil at high voltage.
What do you imagine will happen INSIDE that copper pipe?
I tried it ... and to my surprise, when I switched everything
off, waited several minutes and then attempted to handle
the copper pipe, I got a BIG ZAP on my fingers. Ouch!
The cylinder retained a very large charge.

I think this can be explained by Lenz's law ... and may be
the reason that Hendershot placed his capacitor INSIDE
his coil.

[morpher44]

cylinder

morpher,
what did you use as a base cylinder for your capacitor?

I am using a *pristine-empty* paint-can cylinder which measures:
height: 4.75 in
diameter: 4.25 in
and is a magnetic stainless steel
*unknown permeability*
and purchased at Ace Hardware.

My Hendershot-like coil has a 5 inch diameter ... not 5 15/16ths.

I am not *yet* going for an exact replication of Hendershot's
circuit ... but rather I'm studying various properties of this
device to try to get a feel for what can be changed ... how
its put together ... how to reverse engineer it.

The 5 15/16ths diameter *may* be important ... I don't know.
If Hendershot selected that dimension only because it was
convenient relative to coffee cans he original built the thing
from, then that dimension is not crucial.
If, on the other hand, he selected that dimension due
to some sort of standing wave geometry ... and *special* frequency,
then that diameter becomes very important.

I'm thinking that you can vary this diameter .. because
from what little I know about coils and radio design, etc.
what matters more is the inductance ... and not so much
your coil dimensions -- within limits.
You don't want a coil that is TOO large a diameter and
TOO narrow a height ... unless your trying to build a loop antenna.
You don't want a coil with a very narrow diameter and
a long height ... as the magnetic fields will be very
week. So I imagine this geometry doesn't exactly have
to match ... given you can achieve inductances and resistances
similar to Hendershot.

So I think if you vary the dimensions a bit, like I have done,
you still should observe some effects ... and then as
we understand what is going on, we can optimize
those effects.

[NOMDI]

Handmade Capacitor

@MORPHER 44

Congrats ! I think you're really on something !! Nobody thought about Lenz before you...

But why did Hendershot not use Copper for his tanks ?

Or maybe he used a copper foil for the capacitors ?

...

Sorry for the electric shock but i hope I'll see your experiment on YouTube !

Cheers

[morpher44]

am band?

I'll give you my imagination about coil/capacitor. It was tuned to the local AM (~520KHz) radiostation. And it was building potential difference on a cap ...
The rest is not clear yet, but I'm thinking about it

@mlurye

I've been thinking about this quite a bit ... and here are some thoughts
regarding this topic...

The tank circuit composed of the 7.8nF cap and the 50uH (or so)
would resonate at about 255hz -- very ball park.
This is BELOW the AM band.
Yet, the inductance the cap sees is not exactly 50uH ... and
is rather MUCH MUCH large due to the very odd circuit
on the other side of the 50uH coil. Under it is a 64-turn coil ...
so the two become a transformer -- essentially.
There is a formula -- in circuit analysis -- that provides
a way to calculate at sort of *equivalent* inductance
of a transformer ... given the inductances on either side.
What is interesting about the Henershot circuit is that he
wires things all around through as many inducances in series
as he can .. including the 120/24VAC 5:1 transformers ..
both primary and secondary.
So in terms of an *equivalent* inductance, that 7.8nF
cap sees an inductance -- due to the transformer over
to a weird highly inductive circuit on the other side.
Hence, its resonant frequency is much lower now ...
perhaps in the audio range.

Now comes the debatable part.

Is the capacitor wrapped around a magnetic cylinder or not?

It is probable that when Hendershot originally used coffee cans,
that his cylinder was magnetic.
He may have switched to a non-magnetic stainless steel.

That choice becomes important here in that a cylinder
with permeability will bring the tuned circuit even LOWER
in frequency ... approaching the 100 Hz buzzer frequency.

The reason that resonant frequency is important is that
it allows for certain frequencies to travel through the circuit
w/o attenuation.

However, his circuit is so odd that something else might be
occurring related to polarity change.
His circuit seems to take up spikes ... that dampen ...
and down spikes that dampen ... and turn them
into more of a square wave due to the LRC timing constants
of his big 40MFD, 80MFD caps ... and inductances.
So it is possibly that this tank circuit, while ringing ..
holds the magnet-bar-solenoid in a state whereby
the bar can't commit which direction to go ... towards
the magnet ... or towards the solenoid ... until it
finally SNAPs ... producing a pulse.
I don't really know ... but something is definitely interesting
here ..
and I'm very impressed that there are no DIODES in this
circuit ... just passive components ... coils, caps, transformers....

[morpher44]

nobody before me? -- lol

Congrats ! I think you're really on something !! Nobody thought about Lenz before you...
But why did Hendershot not use Copper for his tanks ?
Or maybe he used a copper foil for the capacitors ?
Sorry for the electric shock but i hope I'll see your experiment on YouTube !
Cheers

I'm a reverse engineer only ... speculating like crazy.
It would be good to have more observations, more
replications, etc.

Lenz's law will work with aluminum as well ... and ... yup... capacitors
have aluminum foil ... don't they?

Be aware, however, that with diamagnetic material in your coil,
your inductance actually DROPS -- the opposite of permeability.

[NOMDI]

@morpher44

I confirm, modern capacitors use aluminium.

My mistake about a copper tank : you re right, the permeability would fall dramatically. It was just thoughts...

The relative permeability is 10 000 for pure iron, 40 000 to 50 000 for steel with 3% of silicon (very high) and 70 000 to 130 000 (huge !) for Mumetal/Permalloy C.

I have no data about aluminium or about amagnetic stainless steel but I just notice that steel with 3% of silicon is well known to be used in the best transformers and inductances and is ...magnetic.

So I dont think amagnetic material has ever been used by Hendershot.
The best compromise between efficiency and availability at his time is probably regular steel...

[morpher44]

the earth's field

Another part of the Hendershot myth is that the Earth's magnetic field
somehow plays a role...

Regarding the statement I just made:

"...ringing holds the magnet-bar-solenoid in a state whereby
the bar can't commit which direction to go ... towards
the magnet ... or towards the solenoid ... until it
finally SNAPs ... producing a pulse.
I don't really know ... but something is definitely interesting
here .."

The ringing in the tank circuit ... is a damped oscillation.
The Earth is rotating in a huge magnetic field and
Hendershot thought of the Earth like a stator in an electric
motor.
Is it possible that as the Earth rotates
and you pass over a certain field line,
that it can create a TWANG or PLUCKING of the
neutral line (ala Wesley Gary) or Bloch Wall?

So like the string of an electric guitar being PLUCKED,
the solenoids may pick up the pluck and pass it along.

Wouldn't that be cool!!! Again I speculate...

[morpher44]

pickup coil technology

One similarity to the sorts of coils Hendershot built for his
early "toy motor" circuit and modern magnetic pickup coils
is that they both have coils wrapped around
permanent magnets (such as AINico).

On a guitar pickup, when you pluck a string, the string
vibrates over the pickup for a time ... producing an
AC waveform that will ring for a while until the string settles down.

A simple experiment with an electric guitar and AMP might be
to put the AMP/guitar just on the very verge of feeding back.
Rotate the guitar to various EARTH orientations:
North-South ...
then
East-West...
Does the guitar go into feedback EASIER on one orientation
versus the other?

I don't have an electric guitar ... but if someone out
there does, would you mind doing this experiment?

Pickup (music technology) - Wikipedia, the free encyclopedia

[morpher44]

"Nuclear spins in the Earth's magnetic field"

This is a very interesting paper:

http://www.google.com/url?sa=t&sourc...TzZI_4r2TriThA

A couple things of note:

* The circuit he presents in his paper is pretty easy ... 555 timers,
741 op-amps, coils, transistors, etc.
He presents this for students who want to mess around with NMR
technology and measure proton spins using the Earth's field.

* The Larmor frequency various, depending upon your location
on the planet. Knowing it, you can measure the spin echo
and actually hear proton rephasing in the audio range ..
or see it on an oscilloscope.

* Two coils are needed ... one polarizing coil, one receiver coil.
The receiver coil is situated INSIDE the other and is oriented
90 degrees within the cylinder of the polarizing coil.

* The coils are NASTY. Converting to inches .. easy for me to
comprehend ..
Polarizing coil: Diameter 6.283 in, Length 6.2992 inch,
560 turns of 14 AWG.
Receiver coil: Diameter 2.938 in, Length 3.937 inch
2700 turns of 30 AWG
I'm immediately struck by the fact that these coils have
a huge number of turns. The receiver coil has a HUGE
resistance which would attenuate the received pulse
from the earth's field by a large margin ..
and the polarizing coils diameter is similar to the Hendershot
diameter.

I'm wondering if a better coil design could pick up
this spin echo better ... providing a larger EMF.

[mlurye]

By the way another thing about Hendershot circuit, it is in a sense symmetrical and balanced. Same parts on the left and right, and 110V 60W load is balanced by 110V buzzer.

[mlurye]

This is a very interesting paper:

http://www.google.com/url?sa=t&sourc...TzZI_4r2TriThA
..............

morpher,
looks like you are going Moray's way. And may be it would be good direction to go in order to find working frequency.

[synchro]

Lervitation circuitry.

ART TEC - Guy Marsden's home page has a levitation kit that might be adapted to work to help oscillate an armature centered on a magnetic neutral line. The electro magnet is wired to apply pulses in both directions based on Opticutter or Hall sensor trigger signals. The armature might need guide magnets to keep on station.

[synchro]

Finally got his sketch to upload! On top is a magnet cushion of a repulsive disk and a ring neos, the disk attached to the solenoid plunger and the ring to the top of the solenoid. The solenoid plunger is attached to the soft iron bar armature, and attracted to the side of the horseshoe magnet. There are opposing tensions. A double pole double throw reed relay is triggered by the top plunger magnet and reverses the polarity of the solenoid, driving the iron bar up and down.