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.



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That would seem to indicate that your idea

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.
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Hans-Bernhard Broeker

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.

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PabloRena ---> AnalProbe

Convert the vibrational energy into electrical energy.

Reply to
Guy Macon

Hello Eric,

Those are always the best, aren't they?

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.

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.

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

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

Reply to
boB Gudgel

Have you looked at batteries as an option?

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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
    PC Services
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Paul Carpenter

Maybe Nikola Tesla has the answer? :)

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Good reply.


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Synchronously for the most part

Like a car driving over a pot hole... the Vibration is a function of the environment this vehicle is in.

-20 to +60 C

Not really... smaller than a bread box.

it is to be mounted on a peice of industrial equipment

The 140mW doesn't have to be constant... because I was planning on using this power to trickle charge a battery.

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I think that by the time you get done with some exotic power coupling system you would be way ahead to use a rechargable battery pack that is easy to replace. A typical laptop battery is 4000 mAH or more and 10 to

12 volts. A battery like this would meet the requirement for a week. Not nearly as interesting.

Dave Rooney

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Dave Rooney

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