charge batteries via inductive coupling

[TonyMatthews]

Sorry I have not replied earlier ?I had trouble with Agent and gave it
up. The ball is solid with no air fill ports or other openings.

 

[TonyMatthews]

No I do not want the charge base to be other than a semisphere shape.
Orienting the ball will not be an issue. I will figure out something
to make it intuitive. Or give feedback when properly positioned.

 

[TonyMatthews]

A brilliant solution I admit. But the orientation is not an issue.
Trust to that. It is the winding s and coil shape and maximum distance
and does the coil work best when stacked or when one is inside the
other that I am trying to determine.
Tony

 

[TonyMatthews]

Actually the trickle charge rate for the battery in question is 150
ma but the ball will draw current for other than charging while on the
charger. So the number is acurate enough. And there is room for
copper.

Hello
I need help figuring out the coil structure for a toy I want to
build. I have a rubber ball with a battery inside. I want to recharge
the battery without a galvanic connection. I'm looking to get about
300 ma charge current. The ball will sit in a cup shaped recharger.
And the coil in the charger will be powered by a wall wart with a
nominal 12 vac output and around 500ma or less.

Just buy an electric toothbrush from OralB, take it apart and use the
elements it has. They charge in their stand without contacts by way of
inductive coupling. There is no way that they operate at 300mA charge
current though. I think you need to key that figure down a bit
realistically speaking. Or maybe not... :-]

 

[TonyMatthews]

OR a charging indicater "glow" that indicates proper orientation.
Perhaps.

 

[TonyMatthews]

Thank you. This is directly responsive to my question and very useful
information. Clearly conveyed as well. Thanks agin
Tony

On Dec 9, 11:43 am, TonyMatthews wrote:

Read the Vladimir reply and the extending of it. After I pressed
"send" I though of another comment I should have made.

[....]

3. I would prefer an air core but it would be nice to know if that was
a mistake.

It doesn't rise to the level of mistake but, adding a core will reduce
the amount of copper you need to use. These days iron is much cheaper
than copper so it would be worth adding some.

Remember that the iron must not go between the two coils. If the ball
fits down inside a cup that makes the windings concentric, you want
the core to be inside the ball. This would be troublesome from a
structural point of view. If you have the cup coil's below the ball's
coil, adding a core below the cups coil could improve the coupling.

ASCII ART:


OOO OOO <--- Ball coil
OOO OOO

OOO OOO <- Power coil
IIIIIIIIIIIIII
IIIIIIIIIIIIII
IIIIIIIIIIIIII <- Iron core
IIIIIIIIIIIIII

The core causes the lines of force to take the longer path around the
Power coil. This makes the field at the Ball coil larger.

4. given the coil on the primary side is x turns what should the coil
on the secondary side be. I need 5 volts or more at 300 ma or so. To
run the ciruitry and have the over head to charge the battery.

5. How can I predict the effect of seperation on the power exchanged
by the two coils? I would like at least an inch between them is this
feasible? And if not what number should I use?

 

[TonyMatthews]

Which amounts to putting the charger coil on the rim and the ball coil
in the balls bottom. Why not use a toroid?

 

[TonyMatthews]

Visual feedback. LED that glows when the charging circuit is happy.

 

[TonyMatthews]

That's pretty smart. Too bad it is unnecessary. I would enjoy
implementing it.
Tony

 

[TonyMatthews]

Well I understand some of that. But turning it into a wire gauge and
approximate number of turns given the input voltage and current still
eludes me.
Thanks for the replies guys. I see the idea was of interest and am
glad I could provide a bit of diversion.
Tony

 

[gearhead]

Which amounts to putting the charger coil on the rim and the ball coil
in the balls bottom. Why not use a toroid?




- Show quoted text -

Are you using Google? Your posts omit the text you are replying to.
In order to make the thread intelligible, please hit "more options"
and "reply." Then your post will include the text you're replying to.

Don't use a toroid because they are self-shielding. You will get
no coupling.

 

[Mike]

Are you using Google? Your posts omit the text you are replying to.
In order to make the thread intelligible, please hit "more options"
and "reply." Then your post will include the text you're replying to.

No they don't. The message he's responding to follows his post (top posting).
If I read it correctly, he's using Forte Agent 4.0/32.1071 through usenetmonster.com

Don't use a toroid because they are self-shielding. You will get
no coupling.

Mike


When truth is absent politics will fill the gap.

 

[ChairmanOfTheBored]

MooseFET [email protected] posted to sci.electronics.design: [..Ball being charged..]
Orienting the ball is part of the problem. Any workable solution
includes orientation.

Yes include:

3 coils in the ball solves this problem.

The shapes of the coils will need to be distorted a bit a the point
where they intersect. I don't think this will reduce the coupling
area enough to matter.

If you make them figure eights, you end up with six coils for the
electrical price of three!

 

[Ross Herbert]

Hello
I need help figuring out the coil structure for a toy I want to
build. I have a rubber ball with a battery inside. I want to recharge
the battery without a galvanic connection. I'm looking to get about
300 ma charge current. The ball will sit in a cup shaped recharger.
And the coil in the charger will be powered by a wall wart with a
nominal 12 vac output and around 500ma or less.
What I need is help in figuring out the shape of the coils and their
positions and the number of turns and so on. I am fairly good with
most electronics but never could grok this inductive stuff. The math
is above me. If I could just get a bit of advice on some basic aspects
like for instance:
1. Would the coil shape for the charger cup be better as a say 1.5"
donut shape mounted in the bottom of the cup just below the surface
with the other coil in the ball just above and stacked like two
donuts, be better than a 3" coil in the rim of the cup with the ball's
coil like a smaller donut in the hole of the larger charger coil's
donut?

2. How do I determine the number of turns I need to limit the current
drawn from the supply to it's rated power output. assuming 60hz at
around 12 vac?

3b. should I be looking at increasing the frequency driving the coil?

3. I would prefer an air core but it would be nice to know if that was
a mistake.

4. given the coil on the primary side is x turns what should the coil
on the secondary side be. I need 5 volts or more at 300 ma or so. To
run the ciruitry and have the over head to charge the battery.

5. How can I predict the effect of seperation on the power exchanged
by the two coils? I would like at least an inch between them is this
feasible? And if not what number should I use?

Here's a paper on an inductively coupled battery charger project
http://www.ele.auckland.ac.nz/~p4p_2004/archive/reports2003/pdfs/p64_rcou026.pdf

It points out a number of factors which you need to consider whatever
method you use. For starters, the switching frequency needs to be
fairly high to keep the size of inductive components small. Then there
is the factor of maximum power transfer efficiency, which this paper
states is around 36% with 20% duty cycle. Then you have to consider
charge regulation etc.....

All in all, it isn't a simple process to do it inductively, so good
luck in your endeavour...

 

[ChairmanOfTheBored]

No I do not want the charge base to be other than a semisphere shape.
Orienting the ball will not be an issue. I will figure out something
to make it intuitive. Or give feedback when properly positioned.

You could use a vibrating base, and when it gets to the coil, the
magnetization effects will lock it in place without any switching or
other circuitry required.

Please REFRAIN from top posting when you are in a Usenet newsgroup.
This ain't e-mail.

 

[Ross Herbert]

On Tue, 11 Dec 2007 02:55:07 GMT, Ross Herbert
You might be able to adapt this design
http://dx.eng.uiowa.edu/power supply paper.pdf and soup it up for
your application. I still can't see how you are going to incorporate
the charge control circuitry inside your ball...

 

[ChairmanOfTheBored]

Which amounts to putting the charger coil on the rim and the ball coil
in the balls bottom. Why not use a toroid?

A toroid keeps all of it flux inside, and there would be no coupling to
any winding that is not actually would around the toroid. Wires and
coils placed near toroidal transformers and coils do not impart any
energy to the proximal wire or coil, unless it is INSIDE the toroid
center hole (not much energy there). It has to actually make turns
around the core to couple with other windings on said core.


STOP top posting!

I can't believe that you are using Agent, and you actually physically
move your cursor above the default position. You are willing to do that,
yet are to lazy to scroll down in a post to read an answer, or make a
reply the proper, chronological way.

Here's a clue... the same amount of effort is involved, lazy ass.

 

[ChairmanOfTheBored]

Are you using Google? Your posts omit the text you are replying to.
In order to make the thread intelligible, please hit "more options"
and "reply." Then your post will include the text you're replying to.

Idiot! Every post he has made has been top posted, and has included
the previous post below it. Also, do you not know how to read a header?

Don't use a toroid because they are self-shielding.

Oh yeah... he'll certainly understand that non-term.

You will get
no coupling.

Nice fact, but devoid of explanation as to why.

 

[ChairmanOfTheBored]

On Tue, 11 Dec 2007 02:55:07 GMT, Ross Herbert
You might be able to adapt this design
http://dx.eng.uiowa.edu/power supply paper.pdf and soup it up for
your application. I still can't see how you are going to incorporate
the charge control circuitry inside your ball...

Me either, as it needs to be near the balls outer surface to work, and
that would require that there be a duplicate mass on the opposite side of
the ball to balance it properly. Unless a wobbly ball has no effect on
his application.

 

[MooseFET]

You might be able to adapt this designhttp://dx.eng.uiowa.edu/power%20supply%20paper.pdfand soup it up for
your application. I still can't see how you are going to incorporate
the charge control circuitry inside your ball...

(A) He doesn't have to put the whole charge controller inside.
(B) The charge controller needs very few parts.

Once the design is set, he knows the primary side to secondary side
transfer function. This means that the primary side controller can
set gross current limits and voltage limits.

A signal can be brought back from inside the ball either inductively
or optically. This means that a simple voltage measurement can be
done inside the ball if needed.

If the control needs to be kept completely inside the ball, a 6 legged
PIC would be more than enough to do the logic and a single transistor
can do the power switching.