Wireless Power Transfer

Have have an interesting problem.

I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
air gap without using a wire.

It will be in a high vibration and dirty (ie. greasy, oilly)
evironment.

Here are my ideas:

1) create an air gap transformer

2) use super bright LED's and a Solar panel

Does any one have any experience or knowledge in this area that could
offer some ideas and literature sources on implementing this.

Thanks,

Eric

Eric <ericjohnholland@hotmail.com> wrote:

> I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
> air gap without using a wire.

> It will be in a high vibration and dirty (ie. greasy, oilly)
> evironment.

That would seem to indicate that your idea 

> 2) use super bright LED's and a Solar panel

is a non-starter.  Light transmission and "greasy, oily" don't mix.

Setting aside really crazy ideas (directed air or liquid flow, cathode
ray tube, ...), magnetic power coupling, i.e. an air coil transformer,
is probably the only available option.

-- 
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

"Eric" <ericjohnholland@hotmail.com> wrote in message
news:1124216703.140608.248550@z14g2000cwz.googlegroups.com...
> Have have an interesting problem.
>
> I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
> air gap without using a wire.
>
> It will be in a high vibration and dirty (ie. greasy, oilly)
> evironment.
>
> Here are my ideas:
>
> 1) create an air gap transformer
>
> 2) use super bright LED's and a Solar panel
>
> Does any one have any experience or knowledge in this area that could
> offer some ideas and literature sources on implementing this.
>
> Thanks,
>
> Eric


I've seen a solid state laser used to transmit light on an optical fiber.
The output of the optical fiber illuminated a solar cell to provide local
power for a wide bandwidth active antenna.  The fiber optic solution for
powering the antenna was used to avoid contaminating the near-field of the
antenna and effectively de-tuning it.  This worked, but there wasn't any
grease to deal with.

If this is not rotating machinery, why don't you use an armored cable.  If
it is rotating machinery, then use something like a distributor in an
automobile.

Eric wrote:
>
>Have have an interesting problem.
>
>I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
>air gap without using a wire.
>
>It will be in a high vibration and dirty (ie. greasy, oilly)
>evironment.
>
>Here are my ideas:
>
>1) create an air gap transformer
>
>2) use super bright LED's and a Solar panel
>
>Does any one have any experience or knowledge in this area that could
>offer some ideas

Convert the vibrational energy into electrical energy.

Hello Eric,

> Have have an interesting problem.

Those are always the best, aren't they?

> I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
> air gap without using a wire.
> 
> It will be in a high vibration and dirty (ie. greasy, oilly)
> evironment.
> 
> Here are my ideas:
> 
> 1) create an air gap transformer

That's the ticket. Make yourself familiar with series resonant 
converters and their use in contactless power transfer. The essence of 
this technology is that while the leakage inductance of your transformer 
becomes huge with increasing distances it is more or less neutralized by 
turning it into part of a series resonant circuit. TI carries lots of 
the previous Unitrode chips that can be used to regulate the frequency.

You didn't say whether the other side needs to be regulated. Probably 
not. If it does then the frequency typcially is varied to achieve this.

2-3 inches is a stretch but you could start out with fairly large 
diameter core halves of a pot core. #77 material, Kaschke K2004 or 
similar. Sometimes they offer a split plastic bobbin carrier which is 
nice, saves you the trip to the machine shop.

> 2) use super bright LED's and a Solar panel

Sounds like brute force, lots of space and $$. Definitely not a viable 
option in an oily and greasy environment. Panels may not like too much 
vibration either.

> Does any one have any experience or knowledge in this area that could
> offer some ideas and literature sources on implementing this.

Use Google to find papers on "Inductively Coupled Power Transfer" and 
similar topics. Lots of medical apps where they have to go through human 
skin and tissue. I forgot the titles but there were some excellent 
papers by Benedetti et al. back in the 90's. I believe they went up to 
70mm which sounds like your distance goal.

The University of Auckland (New Zealand) has done a fair amount of 
research in this area. You will have to become very familiar with 
magnetics and switch mode power supply design if you go that route 
alone. The good news is that your target power level is wimpy compared 
to what we usually deal with. So if your transistors miss the zero 
voltage switch point you won't have to have the fire department come out ;-)

Regards, Joerg

http://www.analogconsultants.com

On 16 Aug 2005 11:25:03 -0700, "Eric" <ericjohnholland@hotmail.com>
wrote:

>Have have an interesting problem.
>
>I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
>air gap without using a wire.
>
>It will be in a high vibration and dirty (ie. greasy, oilly)
>evironment.
>
>Here are my ideas:
>
>1) create an air gap transformer
>
>2) use super bright LED's and a Solar panel
>
>Does any one have any experience or knowledge in this area that could
>offer some ideas and literature sources on implementing this.
>
>Thanks,
>
>Eric


How much surface area do you have available for TX-RX on both sides ??
boB

On 16 Aug 2005 11:25:03 -0700, "Eric" <ericjohnholland@hotmail.com> wrote:

>Have have an interesting problem.
>
>I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
>air gap without using a wire.
>
>It will be in a high vibration and dirty (ie. greasy, oilly)
>evironment.
>
>Here are my ideas:
>
>1) create an air gap transformer
>
>2) use super bright LED's and a Solar panel
>
>Does any one have any experience or knowledge in this area that could
>offer some ideas and literature sources on implementing this.
>
>Thanks,
>
>Eric

Have you looked at batteries as an option?

On 16 Aug, in article
     <1124216703.140608.248550@z14g2000cwz.googlegroups.com>
     ericjohnholland@hotmail.com "Eric" wrote:

>Have have an interesting problem.
>
>I need to transfer power (7V @ 20mA approx. 140mW) across a 2-3 inch
>air gap without using a wire.
>
>It will be in a high vibration and dirty (ie. greasy, oilly)
>evironment.
>
>Here are my ideas:
>
>1) create an air gap transformer
>
>2) use super bright LED's and a Solar panel
>
>Does any one have any experience or knowledge in this area that could
>offer some ideas and literature sources on implementing this.

The main things you don't say

1/  Do both sides vibrate synchronously or asynchrously

2/  Is vibration constant due to operation of environment or like
    driving a car over a pot hole?

3/  What temperature range

4/  Size/volume constraints

5/  Inside or external environment or other special environments like
    aviation, automotive.

There are many ways to transfer or generate power but it depends on the
environment, becuase if this is constantly vibrating you could even consider
a 'shaker' genarator and rechargeable battery, like the shaker torches
that can be got. Similar in energy saving to clockwork radios, wind up
battery chargers etc..

140mW (7V @ 20mA) is similar power to a small torch.

Also if any other movements like circular motions could be used to
generate secondary power.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.gnuh8.org.uk/>              GNU H8 & mailing list info
<http://www.badweb.org.uk/>             For those web sites you hate

Maybe Nikola Tesla has the answer?  :)

On 17 Aug 2005 04:36:55 -0700, "Rob" <mr_horton@yahoo.com> wrote:

>Maybe Nikola Tesla has the answer?  :)

Good reply.

Dan