Driving LEDs with a battery pack

[ehsjr]

greg wrote:

Jon Kirwan wrote:

You mentioned just in
the prior paragraph the "dropping the inductance to zero." But that
doesn't actually happen. What happens is that it goes down to what
amounts to an air/vacuum core.


Yes, I realise that. I really meant it goes down to
something very small compared to the pre-saturation
inductance.

you'd be best off
with no core at all. That doesn't appear to be
the case, so there must be some opposing effect
at work.


I think it is called N. Too many windings are required.


I've come to much the same conclusion. With very low
inductance, the current shoots up to the maximum the
transistor can handle in a very short time, so the
circuit would have to operate at a very high frequency,
and then switching losses would ruin your day.

So it helps to have a moderate amount of inductance
to keep the rate of current increase down to something
manageable. To get that with an air core, you would
have to put on a lot of turns. Using a core with
moderate permeability lets you get away with less
turns. Its energy storage ability will be lower,
but still enough to be useful.

Think of a series resistance circuit where you have some aluminum you
can run out some length of and the some carbon of the same diameter to
make a combined loop.


Another analogy I've seen is that it's like trying to
make a circuit using bare wires immersed in salt water.
Really hard to keep the current from leaking all over
the place!

Anyhow, from what I've seen so far, it sounds like for
frequencies under 100kHz, either a metal powder ring
or a gapped ferrite ring would be best. A solid ferrite
ring, such as a bead, doesn't sound so good.

Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.

Ed

 

[Jon Kirwan]

On Tue, 14 Jul 2009 03:31:27 GMT, ehsjr <ehsjr@NOSPAMverizon.net>
wrote:

snip
Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.

I am keeping it in mind and I am DEFINITELY not focused on inductance.
It's not a goal, it's the result of other goals.

In the gapped core case and if you read my response to the same post
you are responding to here, I wrote, "I guess the secondary wound
elsewhere would be linked well enough by the ring of material so that
flux changes would induce the desired voltage without the kind of
usual poorer linking seen in pure air cases." Note that I brought up
linking where it wasn't mentioned, exactly because that is important
in this case. The base winding is a help in squeezing out the last
bit from a battery.

And although I'm not sure of what I imagine here, I think a gapped
core would link just fine. The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily by
the low reluctance path of the core through the base winding, which
would have the desired induced voltages. I admit I'm not positive on
this point. It just seems 'right' to me. All the core in a gapped
situation does is provide a low reluctance pathway between the north
and south poles of the air. The spiraling electron charges create
linear force lines through the center (a set of fixed magnetic lines
induce a force on any electric charge that is always perpendicular to
the path of the electron motion, causing electrons to naturally spiral
when in motion across a fixed magnetic field... the reverse is also
true, that spiraling electrons must create linear magnetic field
lines.) These magnetic lines yield an N and S and with the rest of
the core, the lines can easily pass to make the necessary closed loop
but via the low reluctance core. So any winding on it should
experience changes in the flux density created in the air gap, I
think.

Jon

 

[greg]

Jon Kirwan wrote:

The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily by
the low reluctance path of the core through the base winding, which
would have the desired induced voltages. I admit I'm not positive on
this point. It just seems 'right' to me.

It seems right to me, too.

Also, since a negligible amount of energy is required
from the base winding, it can be ignored for the purpose
of calculating energy storage needs.

--
Greg

 

[greg]

Jon Kirwan wrote:

The issue here is energy transfer per unit time. You keep thinking in
terms of current and voltage separately. Change the viewpoint.

I don't see how that helps.

If the voltage across the capacitor is nearly
constant, then to get power out of it at a steady
rate, the current needs to be nearly constant as
well.

I don't immediately see a mechanism that ensures
this, because the capacitor voltage will be sitting
right about where the LEDs are starting to conduct
appreciably, and their voltage-current curve is
very nonlinear. So a small change in the capacitor
voltage will result in a large current change.

Perhaps the question I should be asking is: How
do you calculate the ripple in the LED current
when there is no resistor?

--
Greg

 

[greg]

fungus wrote:

I don't doubt you can make a stable stream of pulses but
I bet they had a variable resistor to fine-tune the frequency.

I don't think it was used as a free-running oscillator,
but more like a monostable. You trigger it, and it
produces a pulse of known length.

I've tracked down a reference that I had in the back
of my mind. It's from Digital's "Small Computer Handbook",
talking about pulse amplifier circuits used in the
PDP-8:

"Modules such as the Type W640 use a transformer-coupled
pulse forming circuit to produce standard 400ns and
1us pulses. The time required to saturate the inter-
stage coupling transformer determines the output pulse
duration."

They also give a circuit, which I'll try to find a
way of posting...

--
Greg

 

[greg]

Jon Kirwan wrote:

it seems to me that the
effective permeability listed for any particular core (which is a max
figure) may also tell us just how much effective air gap there is.

I don't think you need to know the actual air gap, just
the average permeability of the core material (taking any
explicitly-introduced gap into account).

If I understand correctly, the energy stored per unit volume
in the magnetic field depends on the strength of the B field
and the permeability of the material it's passing through.
So knowing the average permeability and the total volume of
the core plus gaps, you can calculate the energy stored per
unit of B. Knowing the value of B needed to saturate the
core material then tells you how much energy the core can
store in total before saturation.

I'm not sure that you really need to involve energy in
the calculation for the purpose at hand, though. The goal
is to build up a certain current I in a time that's not too
short or too long.

Knowing the average permeability and the geometry lets
you calculate the inductance for a given number of turns.
So you can choose a number of turns giving you an
inductance that results in a suitable period. But you
need to check that the B produced by those turns at
current I doesn't exceed the saturation value.

If the number of turns required to give the desired
inductance is excessive, you need to use a core with a
higher permeability.

If the core is going to saturate, you need to use
one that won't saturate so easily, which probably
means using a higher permeability material or adding
more air gap.

That will lower the inductance, which will reduce the
period. If it makes the period too small, you'll have
to add more turns to bring the inductance up again.
But that will raise B, bringing the core closer to
saturation...

At this point my head is starting to hurt. I think
we need an equation linking all these things together,
to make the effect they have on each other more
apparent.

--
Greg

 

[greg]

Here's the pulse transformer circuit I mentioned
earlier.

Haven't quite nutted out exactly how it works yet.
Seems to have some similarities to the Joule Thief
circuit, but there are some tricky things going on
with feedback.


-3V

|
.--------------o----------------------------.
| | |
| V |
| - |
| | |
| | |
| .-------o--------o--------. |
| | | | | | .---
| | | | | .---. |
| --- V .-. .-. *| | |
| --- - | | 3k | | 750 C| |C |C
| | | | | | | C| |C |C Output
|/ | | '-' '-' C| |C |C
---| | === | | | |* |
|> | GND | o--------' | |
| | | | | '---
| | | - |
| | | ^ |
| | | | |/
'------o------------------------------------|
| | | |>
| | | |
| ___ | | ___ |
'-----|___|------o--------o---|___|----'
|
390 | 10
|
|

-15V

--
Greg

 

[Jon Kirwan]

On Tue, 14 Jul 2009 22:13:50 +1200, greg <greg@cosc.canterbury.ac.nz>
wrote:

Here's the pulse transformer circuit I mentioned
earlier.

Haven't quite nutted out exactly how it works yet.
Seems to have some similarities to the Joule Thief
circuit, but there are some tricky things going on
with feedback.


-3V

|
.--------------o----------------------------.
| | |
| V |
| - |
| | |
| | |
| .-------o--------o--------. |
| | | | | | .---
| | | | | .---. |
| --- V .-. .-. *| | |
| --- - | | 3k | | 750 C| |C |C
| | | | | | | C| |C |C Output
|/ | | '-' '-' C| |C |C
---| | === | | | |* |
|> | GND | o--------' | |
| | | | | '---
| | | - |
| | | ^ |
| | | | |/
'------o------------------------------------|
| | | |
| | | |
| ___ | | ___ |
'-----|___|------o--------o---|___|----'
|
390 | 10
|
|

-15V

Base unconnected on that transistor?

Jon

 

[Jon Kirwan]

On Tue, 14 Jul 2009 19:56:09 +1200, greg <greg@cosc.canterbury.ac.nz>
wrote:

Jon Kirwan wrote:
The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily by
the low reluctance path of the core through the base winding, which
would have the desired induced voltages. I admit I'm not positive on
this point. It just seems 'right' to me.

It seems right to me, too.

Also, since a negligible amount of energy is required
from the base winding, it can be ignored for the purpose
of calculating energy storage needs.

Yes.

Jon

 

[Jon Kirwan]

On Tue, 14 Jul 2009 19:59:04 +1200, greg <greg@cosc.canterbury.ac.nz>
wrote:

Jon Kirwan wrote:

The issue here is energy transfer per unit time. You keep thinking in
terms of current and voltage separately. Change the viewpoint.

I don't see how that helps.

If the voltage across the capacitor is nearly
constant, then to get power out of it at a steady
rate, the current needs to be nearly constant as
well.

I don't immediately see a mechanism that ensures
this, because the capacitor voltage will be sitting
right about where the LEDs are starting to conduct
appreciably, and their voltage-current curve is
very nonlinear. So a small change in the capacitor
voltage will result in a large current change.

Perhaps the question I should be asking is: How
do you calculate the ripple in the LED current
when there is no resistor?

The reason I mentioned that is that the BJT/transformer/resistor (plus
battery voltage) set the power and frequency of delivery of increments
of it. (Actually, the transformer doesn't have anything to do with
the power, just frequency of operation.) The frequency determines how
much of it is parceled out per unit time. So if the power is P and
the frequency is f, then it is pulsed with energy equal to (P/f.)
Meanwhile, the LEDs take their power, as well.

LEDs can be treated as linear for purposes of small changes about a
nearby operating condition, so that the power of the LED is P_led(V) =
(V/R_led)*(V-V_start), where R_led and V_start are those two modeling
parameters I've talked about. The change in voltage on the capacitor,
when it is pulsed with a bit of energy from the collector winding,
will be tiny because the energy is added to a capacitor that is
already packed up with energy. Two states are: V(1)^2*C/2 before the
pulse and V(2)^2*C/2, after. The difference is (V(2)^2-V(1)^2)*C/2.
Assume the energy delivered is P/f and V(1) = 20V (stack of 6 LEDs at
their operating point of 3.3V, rounded up.) Compute V(2), selecting
some chosen C value. Call f=50kHz, C=470uF (well, that's what the OP
said he was using!) Since they are operating at a presumed 20mA, we
must assume that the circuit is designed to deliver 20V*20mA or 400mW.

V(2) = SQRT( 2 * 400mW / (50kHz* 470uF) + 20V^2)

or, 20.00085V

So the voltage went up about 850uV. Not all that much, really.

I just wanted you to think about in energy terms. The ripple on the
cap would be huge if the starting voltage of the cap were zero volts
-- almost 185mV change for the first pulse. But once the cap is
charged up, ripple is actually quite modest... under 1mV per pulse.
This really is NOT going to change the power through the LEDs that
much.

Jon

 

[greg]

Jon Kirwan wrote:

Base unconnected on that transistor?

The book didn't show the whole circuit, just the output
stage. Presumably the base is connected to something
which turns the transistor on when a triggering pulse
is received.

--
Greg

 

[greg]

Jon Kirwan wrote:

So the voltage went up about 850uV. Not all that much, really.

Okay, I see what you mean now. You're right, if the
capacitor is big enough, the dynamic resistance of the
LEDs won't change much over the ripple range.

Also, conservation of energy ensures that the voltage
will settle at a point where the average LED current
is at a predictable level. Quite a neat system, really.
The LEDs function as their own built-in current
regulator!

So yes, using a capacitor makes sense if you've got
room for it.

There's just one other thing that was bothering me. I
had something in the back of my mind about LEDs being
more efficient when pulsed. But after reading the
discussion about it here:

http://members.misty.com/don/ledp.html

it seems that this only applies if the maximum current
you have available is a lot less than the optimum
rated current of the LED. If you do have enough current,
then you'll get the most light by running them
continuously at their rated current.

That will be true in our case provided that the battery
can supply enough power.

--
Greg

 

[ehsjr]

Jon Kirwan wrote:

On Tue, 14 Jul 2009 03:31:27 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


snip
Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.


I am keeping it in mind and I am DEFINITELY not focused on inductance.
It's not a goal, it's the result of other goals.

In the gapped core case and if you read my response to the same post
you are responding to here, I wrote, "I guess the secondary wound
elsewhere would be linked well enough by the ring of material so that
flux changes would induce the desired voltage without the kind of
usual poorer linking seen in pure air cases." Note that I brought up
linking where it wasn't mentioned, exactly because that is important
in this case. The base winding is a help in squeezing out the last
bit from a battery.

And although I'm not sure of what I imagine here, I think a gapped
core would link just fine. The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily by
the low reluctance path of the core through the base winding, which
would have the desired induced voltages. I admit I'm not positive on
this point. It just seems 'right' to me. All the core in a gapped
situation does is provide a low reluctance pathway between the north
and south poles of the air. The spiraling electron charges create
linear force lines through the center (a set of fixed magnetic lines
induce a force on any electric charge that is always perpendicular to
the path of the electron motion, causing electrons to naturally spiral
when in motion across a fixed magnetic field... the reverse is also
true, that spiraling electrons must create linear magnetic field
lines.) These magnetic lines yield an N and S and with the rest of
the core, the lines can easily pass to make the necessary closed loop
but via the low reluctance core. So any winding on it should
experience changes in the flux density created in the air gap, I
think.

Jon

Well, you don't _need_ a core, at all. An air wound coil
works well. (A ferrite core may work better, but that is
not the point I'm addressing.)

To make this repeatable for anyone who wants to try, I used readily
available material: 1/2 inch PVC pipe as the coil form, and CAT5
cable from which I extracted one of the 4 twisted pairs. The
extracted pair gives you bifilar. I wrapped a single layer close
wound, 40 bifilar turns around the pvc. I used the "standard" joule
thief circuit with a red LED, and changed the base resistor value to
51 ohms. No output cap or catch diode. It makes the red LED glow
merrily and runs at ~660 khz. Best of all, while it does glow less
brightly as the voltage is lowered, it produces easily visible and
useful glow all the way down below .50 v supply. There is a kind of
"knee" in the brightness at about .44 volts and the glow is just
barely detectable at about .38 volts. I imagine those values will
differ slightly with different layout, different NPN (mine is 2n3904),
etc. A caveat - there is significant loss in my setup between the
power supply and the breadboard, and that contributes positively to
the operation. I'm flying in the dark, trying to simulate a weak
battery by the seat of my pants. I don't know what the impedance of
a "weak" battery is. I do know that if I bypass the supply where it
is delivered to the bread board with 100 uF, the glow gets dimmer.
I may find time to fiddle with the supply Z and post some numbers
on that as well as Ice, but really, it was not the intent to optomize
or even fully measure things. The purpose was to devise an easily
repeatable experiment that proves that core saturation is not
needed. You don't even need a core at all to steal joules.

Ed

 

[Jon Kirwan]

On Fri, 17 Jul 2009 07:07:44 GMT, ehsjr <ehsjr@NOSPAMverizon.net>
wrote:

Jon Kirwan wrote:
On Tue, 14 Jul 2009 03:31:27 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


snip
Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.


I am keeping it in mind and I am DEFINITELY not focused on inductance.
It's not a goal, it's the result of other goals.

In the gapped core case and if you read my response to the same post
you are responding to here, I wrote, "I guess the secondary wound
elsewhere would be linked well enough by the ring of material so that
flux changes would induce the desired voltage without the kind of
usual poorer linking seen in pure air cases." Note that I brought up
linking where it wasn't mentioned, exactly because that is important
in this case. The base winding is a help in squeezing out the last
bit from a battery.

And although I'm not sure of what I imagine here, I think a gapped
core would link just fine. The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily by
the low reluctance path of the core through the base winding, which
would have the desired induced voltages. I admit I'm not positive on
this point. It just seems 'right' to me. All the core in a gapped
situation does is provide a low reluctance pathway between the north
and south poles of the air. The spiraling electron charges create
linear force lines through the center (a set of fixed magnetic lines
induce a force on any electric charge that is always perpendicular to
the path of the electron motion, causing electrons to naturally spiral
when in motion across a fixed magnetic field... the reverse is also
true, that spiraling electrons must create linear magnetic field
lines.) These magnetic lines yield an N and S and with the rest of
the core, the lines can easily pass to make the necessary closed loop
but via the low reluctance core. So any winding on it should
experience changes in the flux density created in the air gap, I
think.

Jon

Well, you don't _need_ a core, at all. An air wound coil
works well. (A ferrite core may work better, but that is
not the point I'm addressing.)

To make this repeatable for anyone who wants to try, I used readily
available material: 1/2 inch PVC pipe as the coil form, and CAT5
cable from which I extracted one of the 4 twisted pairs. The
extracted pair gives you bifilar. I wrapped a single layer close
wound, 40 bifilar turns around the pvc. I used the "standard" joule
thief circuit with a red LED, and changed the base resistor value to
51 ohms. No output cap or catch diode. It makes the red LED glow
merrily and runs at ~660 khz. Best of all, while it does glow less
brightly as the voltage is lowered, it produces easily visible and
useful glow all the way down below .50 v supply. There is a kind of
"knee" in the brightness at about .44 volts and the glow is just
barely detectable at about .38 volts. I imagine those values will
differ slightly with different layout, different NPN (mine is 2n3904),
etc. A caveat - there is significant loss in my setup between the
power supply and the breadboard, and that contributes positively to
the operation. I'm flying in the dark, trying to simulate a weak
battery by the seat of my pants. I don't know what the impedance of
a "weak" battery is. I do know that if I bypass the supply where it
is delivered to the bread board with 100 uF, the glow gets dimmer.
I may find time to fiddle with the supply Z and post some numbers
on that as well as Ice, but really, it was not the intent to optomize
or even fully measure things. The purpose was to devise an easily
repeatable experiment that proves that core saturation is not
needed. You don't even need a core at all to steal joules.

Ed

Thanks, Ed. This confirms my earlier analysis about it, in spades.
Unless someone wants to argue that it is the PVC part of it that
saturated and made it work. I like the idea of taking cat5 cable
(or cat6, which is what I have laying about) and stripping out the
twisted pairs for winding. I'm going to try that, despite having so
much magnet wire laying about. Can you provide all the dimensions of
your air core, though? I'm curious about the approximate inductance
-- for frequency calculations, as I'm wondering if part of the reason
it was only 660kHz had more to do with the NPN than the transformer.
Oh, and did you lay all of the 40 turns side by side, or stacked in
any way?

Thanks again,
Jon

 

[baron]

Jon Kirwan Inscribed thus:

On Fri, 17 Jul 2009 07:07:44 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:

Jon Kirwan wrote:
On Tue, 14 Jul 2009 03:31:27 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


snip
Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.


I am keeping it in mind and I am DEFINITELY not focused on
inductance. It's not a goal, it's the result of other goals.

In the gapped core case and if you read my response to the same post
you are responding to here, I wrote, "I guess the secondary wound
elsewhere would be linked well enough by the ring of material so
that flux changes would induce the desired voltage without the kind
of
usual poorer linking seen in pure air cases." Note that I brought
up linking where it wasn't mentioned, exactly because that is
important
in this case. The base winding is a help in squeezing out the last
bit from a battery.

And although I'm not sure of what I imagine here, I think a gapped
core would link just fine. The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily
by the low reluctance path of the core through the base winding,
which
would have the desired induced voltages. I admit I'm not positive
on
this point. It just seems 'right' to me. All the core in a gapped
situation does is provide a low reluctance pathway between the north
and south poles of the air. The spiraling electron charges create
linear force lines through the center (a set of fixed magnetic lines
induce a force on any electric charge that is always perpendicular
to the path of the electron motion, causing electrons to naturally
spiral when in motion across a fixed magnetic field... the reverse
is also true, that spiraling electrons must create linear magnetic
field
lines.) These magnetic lines yield an N and S and with the rest of
the core, the lines can easily pass to make the necessary closed
loop
but via the low reluctance core. So any winding on it should
experience changes in the flux density created in the air gap, I
think.

Jon

Well, you don't _need_ a core, at all. An air wound coil
works well. (A ferrite core may work better, but that is
not the point I'm addressing.)

To make this repeatable for anyone who wants to try, I used readily
available material: 1/2 inch PVC pipe as the coil form, and CAT5
cable from which I extracted one of the 4 twisted pairs. The
extracted pair gives you bifilar. I wrapped a single layer close
wound, 40 bifilar turns around the pvc. I used the "standard" joule
thief circuit with a red LED, and changed the base resistor value to
51 ohms. No output cap or catch diode. It makes the red LED glow
merrily and runs at ~660 khz. Best of all, while it does glow less
brightly as the voltage is lowered, it produces easily visible and
useful glow all the way down below .50 v supply. There is a kind of
"knee" in the brightness at about .44 volts and the glow is just
barely detectable at about .38 volts. I imagine those values will
differ slightly with different layout, different NPN (mine is 2n3904),
etc. A caveat - there is significant loss in my setup between the
power supply and the breadboard, and that contributes positively to
the operation. I'm flying in the dark, trying to simulate a weak
battery by the seat of my pants. I don't know what the impedance of
a "weak" battery is. I do know that if I bypass the supply where it
is delivered to the bread board with 100 uF, the glow gets dimmer.
I may find time to fiddle with the supply Z and post some numbers
on that as well as Ice, but really, it was not the intent to optomize
or even fully measure things. The purpose was to devise an easily
repeatable experiment that proves that core saturation is not
needed. You don't even need a core at all to steal joules.

Ed

Thanks, Ed. This confirms my earlier analysis about it, in spades.
Unless someone wants to argue that it is the PVC part of it that
saturated and made it work.

If you recall, in a previous post, I mentioned that I had tried an air
core on a 5mm former. I also mentioned that putting a core in improved
the behaviour.

I like the idea of taking cat5 cable
(or cat6, which is what I have laying about) and stripping out the
twisted pairs for winding. I'm going to try that, despite having so
much magnet wire laying about. Can you provide all the dimensions of
your air core, though? I'm curious about the approximate inductance
-- for frequency calculations, as I'm wondering if part of the reason
it was only 660kHz had more to do with the NPN than the transformer.
Oh, and did you lay all of the 40 turns side by side, or stacked in
any way?

Thanks again,
Jon

--
Best Regards:
Baron.

 

[ehsjr]

Jon Kirwan wrote:

On Fri, 17 Jul 2009 07:07:44 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


Jon Kirwan wrote:

On Tue, 14 Jul 2009 03:31:27 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:



snip
Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.


I am keeping it in mind and I am DEFINITELY not focused on inductance.
It's not a goal, it's the result of other goals.

In the gapped core case and if you read my response to the same post
you are responding to here, I wrote, "I guess the secondary wound
elsewhere would be linked well enough by the ring of material so that
flux changes would induce the desired voltage without the kind of
usual poorer linking seen in pure air cases." Note that I brought up
linking where it wasn't mentioned, exactly because that is important
in this case. The base winding is a help in squeezing out the last
bit from a battery.

And although I'm not sure of what I imagine here, I think a gapped
core would link just fine. The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily by
the low reluctance path of the core through the base winding, which
would have the desired induced voltages. I admit I'm not positive on
this point. It just seems 'right' to me. All the core in a gapped
situation does is provide a low reluctance pathway between the north
and south poles of the air. The spiraling electron charges create
linear force lines through the center (a set of fixed magnetic lines
induce a force on any electric charge that is always perpendicular to
the path of the electron motion, causing electrons to naturally spiral
when in motion across a fixed magnetic field... the reverse is also
true, that spiraling electrons must create linear magnetic field
lines.) These magnetic lines yield an N and S and with the rest of
the core, the lines can easily pass to make the necessary closed loop
but via the low reluctance core. So any winding on it should
experience changes in the flux density created in the air gap, I
think.

Jon

Well, you don't _need_ a core, at all. An air wound coil
works well. (A ferrite core may work better, but that is
not the point I'm addressing.)

To make this repeatable for anyone who wants to try, I used readily
available material: 1/2 inch PVC pipe as the coil form, and CAT5
cable from which I extracted one of the 4 twisted pairs. The
extracted pair gives you bifilar. I wrapped a single layer close
wound, 40 bifilar turns around the pvc. I used the "standard" joule
thief circuit with a red LED, and changed the base resistor value to
51 ohms. No output cap or catch diode. It makes the red LED glow
merrily and runs at ~660 khz. Best of all, while it does glow less
brightly as the voltage is lowered, it produces easily visible and
useful glow all the way down below .50 v supply. There is a kind of
"knee" in the brightness at about .44 volts and the glow is just
barely detectable at about .38 volts. I imagine those values will
differ slightly with different layout, different NPN (mine is 2n3904),
etc. A caveat - there is significant loss in my setup between the
power supply and the breadboard, and that contributes positively to
the operation. I'm flying in the dark, trying to simulate a weak
battery by the seat of my pants. I don't know what the impedance of
a "weak" battery is. I do know that if I bypass the supply where it
is delivered to the bread board with 100 uF, the glow gets dimmer.
I may find time to fiddle with the supply Z and post some numbers
on that as well as Ice, but really, it was not the intent to optomize
or even fully measure things. The purpose was to devise an easily
repeatable experiment that proves that core saturation is not
needed. You don't even need a core at all to steal joules.

Ed


Thanks, Ed. This confirms my earlier analysis about it, in spades.
Unless someone wants to argue that it is the PVC part of it that
saturated and made it work.

They can argue - but they would be wrong. In spades.
To prove that, just take about 8 or 9 feet of the
twisted pair. Don't wrap it into a coil - just
connect it to replace the transformer, and the thing
plays fine.

I like the idea of taking cat5 cable
(or cat6, which is what I have laying about) and stripping out the
twisted pairs for winding. I'm going to try that, despite having so
much magnet wire laying about. Can you provide all the dimensions of
your air core, though? I'm curious about the approximate inductance
-- for frequency calculations, as I'm wondering if part of the reason
it was only 660kHz had more to do with the NPN than the transformer.

Frequency is very much voltage dependent. The 660 khz occurs
at .4657 volts. Run the voltage up to around .8 and it runs at
~ 200 khz. If you set aside consideration of the value of L and
the frequency value, just analyze the circuit, and the reason
for the delta F becomes obvious.
You have Vsupply + Vinductor = Vtotal and Vtotal lights the LED.
Current through the LED discharges L. But the LED stops conducting
when Vtotal < Vf causing the pulse in T1. The time taken to
discharge depends upon Vtotal, and Vtotal is lower when the battery
voltage is lower. Therefore, the frequency rises as Vbatt
decreases. This is easily confirmed experimentally.
I did it today with a battery instead of my supply to avoid the
jury rigged attempt to make the supply look like a "weak"
battery.

Regarding the NPN limiting the frequency - it'll run a lot
faster in this circuit with different L. I had it running
at ~1.3 mhz with one of the setups I played with.

Getting back to your specific question about the inductor,
I don't think actual dimensions matter for demonstrating
that air cores work, but here they are:
PVC form is 1/2" dia sched 40. (The od measures 13/16")
The length of the PVC is 3 1/4" and the windings occupy
2 3/4" of that. I drilled little a little hole 1/4" in
from each end and passed the wire through - that way, the
coil doesn't unwrap. To make it, I stripped 20' of
twisted pair out of the CAT5 and close wound it tightly, one
layer, around the form. I left 1' of twisted pair sticking
out of each end, and had 8' 8" of twisted pair left over.
So there's 9' 4" of wire in the coil itself with 1' leads
at each end to connect to the breadboard. Each coil's
inductance measures 10.96 uH.

Oh, and did you lay all of the 40 turns side by side, or stacked in
any way?

Side by side turns, no stacking, just close wound. I can send you a
photo if you want.

Ed

Thanks again,
Jon

 

[ehsjr]

baron wrote:

Jon Kirwan Inscribed thus:


On Fri, 17 Jul 2009 07:07:44 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


Jon Kirwan wrote:

On Tue, 14 Jul 2009 03:31:27 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:



snip
Maybe I missed it, but I get the sinking feeling that the
discussion is overlooking coupling. You both seem focused
on inductance, but I don't see where you are considering
it (coupling). Jon raised the issue earlier, but we didn't
go very far with it.


I am keeping it in mind and I am DEFINITELY not focused on
inductance. It's not a goal, it's the result of other goals.

In the gapped core case and if you read my response to the same post
you are responding to here, I wrote, "I guess the secondary wound
elsewhere would be linked well enough by the ring of material so
that flux changes would induce the desired voltage without the kind
of
usual poorer linking seen in pure air cases." Note that I brought
up linking where it wasn't mentioned, exactly because that is
important
in this case. The base winding is a help in squeezing out the last
bit from a battery.

And although I'm not sure of what I imagine here, I think a gapped
core would link just fine. The key is to wind the collector winding
over the gap and the base winding over the core, elsewhere. Flux
changes in the air gap as energy builds up would be linked readily
by the low reluctance path of the core through the base winding,
which
would have the desired induced voltages. I admit I'm not positive
on
this point. It just seems 'right' to me. All the core in a gapped
situation does is provide a low reluctance pathway between the north
and south poles of the air. The spiraling electron charges create
linear force lines through the center (a set of fixed magnetic lines
induce a force on any electric charge that is always perpendicular
to the path of the electron motion, causing electrons to naturally
spiral when in motion across a fixed magnetic field... the reverse
is also true, that spiraling electrons must create linear magnetic
field
lines.) These magnetic lines yield an N and S and with the rest of
the core, the lines can easily pass to make the necessary closed
loop
but via the low reluctance core. So any winding on it should
experience changes in the flux density created in the air gap, I
think.

Jon

Well, you don't _need_ a core, at all. An air wound coil
works well. (A ferrite core may work better, but that is
not the point I'm addressing.)

To make this repeatable for anyone who wants to try, I used readily
available material: 1/2 inch PVC pipe as the coil form, and CAT5
cable from which I extracted one of the 4 twisted pairs. The
extracted pair gives you bifilar. I wrapped a single layer close
wound, 40 bifilar turns around the pvc. I used the "standard" joule
thief circuit with a red LED, and changed the base resistor value to
51 ohms. No output cap or catch diode. It makes the red LED glow
merrily and runs at ~660 khz. Best of all, while it does glow less
brightly as the voltage is lowered, it produces easily visible and
useful glow all the way down below .50 v supply. There is a kind of
"knee" in the brightness at about .44 volts and the glow is just
barely detectable at about .38 volts. I imagine those values will
differ slightly with different layout, different NPN (mine is 2n3904),
etc. A caveat - there is significant loss in my setup between the
power supply and the breadboard, and that contributes positively to
the operation. I'm flying in the dark, trying to simulate a weak
battery by the seat of my pants. I don't know what the impedance of
a "weak" battery is. I do know that if I bypass the supply where it
is delivered to the bread board with 100 uF, the glow gets dimmer.
I may find time to fiddle with the supply Z and post some numbers
on that as well as Ice, but really, it was not the intent to optomize
or even fully measure things. The purpose was to devise an easily
repeatable experiment that proves that core saturation is not
needed. You don't even need a core at all to steal joules.

Ed

Thanks, Ed. This confirms my earlier analysis about it, in spades.
Unless someone wants to argue that it is the PVC part of it that
saturated and made it work.


If you recall, in a previous post, I mentioned that I had tried an air
core on a 5mm former. I also mentioned that putting a core in improved
the behaviour.

I was curious about that. What did you use for the form? Finding a
~.2" dia form here would be tough without knowing what to look for.
Maybe aquarium tubing? What were the coil dimensions? In the post
you mention, you said it would oscillate, but only without a load.
Is it the "standard" joule thief circuit but without an LED? Did
you try changing the base resistor?

Thanks,
Ed

I like the idea of taking cat5 cable
(or cat6, which is what I have laying about) and stripping out the
twisted pairs for winding. I'm going to try that, despite having so
much magnet wire laying about. Can you provide all the dimensions of
your air core, though? I'm curious about the approximate inductance
-- for frequency calculations, as I'm wondering if part of the reason
it was only 660kHz had more to do with the NPN than the transformer.
Oh, and did you lay all of the 40 turns side by side, or stacked in
any way?

Thanks again,
Jon

 

[fungus]

On Jul 17, 6:25 pm, ehsjr <eh...@NOSPAMverizon.net> wrote:

They can argue - but they would be wrong. In spades.
To prove that, just take about 8 or 9 feet of the
twisted pair. Don't wrap it into a coil - just
connect it to replace the transformer, and the thing
plays fine.

In that case where is the energy stored...?

I thought the Joule Thief worked by storing energy
somewhere then releasing it when the transistor
switches.

/Still waiting for my magnet wire to arrive - I had to
order some on eBay.

 

[ehsjr]

fungus wrote:

On Jul 17, 6:25 pm, ehsjr <eh...@NOSPAMverizon.net> wrote:

They can argue - but they would be wrong. In spades.
To prove that, just take about 8 or 9 feet of the
twisted pair. Don't wrap it into a coil - just
connect it to replace the transformer, and the thing
plays fine.



In that case where is the energy stored...?

I thought the Joule Thief worked by storing energy
somewhere then releasing it when the transistor
switches.

/Still waiting for my magnet wire to arrive - I had to
order some on eBay.

The energy is stored in exactly the same "place" whether using
an air wound or ferrite core transformer: the magnetic field.

When you have a transformer wound on a core of magnetic material
the magnetic field is concentrated in the core. With an air
wound transformer, the magnetic field is not as concentrated,
it occupies a larger volume.

In all cases, the energy is stored in the magnetic field,
regardless of where that field is - in a ferrous core or in air.

Ed

 

[fungus]

On Jul 19, 3:40 am, ehsjr <eh...@NOSPAMverizon.net> wrote:

In all cases, the energy is stored in the magnetic field,
regardless of where that field is - in a ferrous core or in air.

So there's some energy stored in the air around the wire?

That's too weird for my tiny brain.