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Possible alternatives to Power-Over-Fiber?

  1. Aug 14, 2008 #1

    Mech_Engineer

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    Engineers and scientists working in electro-optical diagnostic fields in the past few decades have been fighting with a problem usually not seen under "normal" environmental circumstances, in that diagnostics on high-powered pulsed-power facilities such as NIF (http://en.wikipedia.org/wiki/National_Ignition_Facility) must be totally grounded against EMP to ensure accurate measurements in their insruments.

    The EMP and RF noise emitted by NIF is so intense even small holes for a wire going into the shielding can play havoc with any measurments being taken, in addition to the fact that long wires tend to act as antennas. All pulsed power facilities (that I have worked in) use fiber-optic network cables to transmit data throughout the building for this very reason. Fiber optic cables are non-conductive and use light to transmit information rather than electrical current, which is advantageous in noisy RF environments. Although fiber-optics can fluoresce when bombarded with certain kinds of radiation, this tends to be less of a problem than RF/EM noise in conductors.

    So data transmission can be done over fiber to help maintain low signal-to-noise ratios, but power going to these diagnostics is still dependent on conductors. For this reason, much new research is going into Power Over Fiber (http://www.rp-photonics.com/power_over_fiber.html), basically transmitting small amounts of power (on the order of 1 watt) using a laser on one end and photovoltaic cells on the other.

    It is my contention that power-over-fiber is not the only possible alternative for transmitting power over a distance of around 150 ft. One possibility I thought of off the top of my head would be pneumatic power transmission using a small compressor on one end operating at around 150psi, plastic tubing for the pressure line, and a small turbine/generator on the other end (when I say small turbine, I'm talking around the size of a Dentist's drill). Using some basic voltage/current control circuitry you could have a small power transmission circuit without the use of conductors.

    So, what ideas do you people have for the transmission of small amounts of power around 150 ft wihout the use of electrical conductors? I most interested in what might already be available as off-the-shelf products, but brainstorming is good too.
     
    Last edited: Aug 14, 2008
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  3. Aug 14, 2008 #2

    mgb_phys

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    The advantage of light is the small size, and you can generate a stable 5v supply directly from the photodiode/solar cell.
    The air (or hydraulic) turbine gives you much more power but needs more space and more components to regulate the output.

    Could you use hot water/oil and thermocouples - especially if you have waste hot water from a highpower laser/x ray or capacitor banks.

    I would probably just use batteries/supercaps and disconnect the supply before firing - these experiments are normally over pretty fast so you don't need much power for very long.
     
  4. Aug 14, 2008 #3

    Mech_Engineer

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    You're probably right about the size of the POF system, but safety and price could be concerns. To transmit 1 W of power from one spot to another, your laser would probably have to be around 2 Watts; That's a pretty hefty laser (expensive) and if the fiber breaks you've got an uncontrolled beam of potentially hazardous laser light...

    It seems to me that a relatively low-pressure pneumatic system would be minimally hazardous, and coud be scaled to somewhat higher power requirements than can currently be achieved with power-over-fiber technologies.

    Waste heat is an interesting idea, but it can be difficult to find a "significant" source of waste heat sometimes.

    I am currently project which will use a sealed lead-acid battery for power and will charge it between shots. Discussions of this project have brought to light the apparent absence of small scale off-the-shelf alternative power transmission systems. I'm not really interested in developing a power transmission system for the particular project I am working on now, however I may be interested in applying for some money to develop an alternative to power-over-fiber in an R&D project.
     
    Last edited: Aug 14, 2008
  5. Aug 15, 2008 #4

    berkeman

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    How about distributed batteries (like 12V gel cells) with periodic recharging when the ignition hardware is not operating? Use relays to disconnect the conductors from the local batteries while they are in use providing power to the instrumentation?
     
  6. Aug 18, 2008 #5

    Mech_Engineer

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    Something like that sounds like a good idea, but in many applications the purpose of a non-conductive power transmission technique like power-over-fiber is to have a high-potential floating ground on one side (such as electronics very close to a high-voltage power system), where a relay might not have the necessary insulating capability to prevent arcing.

    What you're suggesting in terms of a battery pack sounds like it could be a good idea for the powered end of an alternative power transmission system however.
     
  7. Aug 18, 2008 #6
    How about a simple methanol fuel cell? They make the things pretty small and compact now so they can be used for cameras and such things. If you need everlasting power you could just buy some fuel line and just run it to the cell. The only problem is you have to buy/reform methanol.

    I think your laser solution is pretty good though. Although I wouldn't use an actual solar panel but more of an array of photo diodes. It would be an efficient way to transmit power.
     
    Last edited: Aug 18, 2008
  8. Aug 18, 2008 #7

    mgb_phys

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    A useful tip for the photodiode (thanks Philip Hobbs) is to put the diode at an angle to the fibre, and have a second diode (connected in parallel) at right angles to the first diode. Any light reflected from the front surface of the first diode, is picked up by the second. A lot cheaper than trying to do a good AR coating on a diode!
     
  9. Aug 18, 2008 #8

    Mech_Engineer

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    It's a cool idea, but having flammable liquids being transported through lines would be a pretty big safety concern.

    The laser idea is a good one that many people are working on, but to transmit 1 watt of power, you would need a laser that is rated for at least 1 watt continuous operation, possibly as high as 2 watts depending on light-electricity conversion efficiency. That sounds like it could be a big, expensive laser to me...
     
  10. Aug 19, 2008 #9
    Why not just use an array of 200mW-ish photodiodes. Big lasers come with big issues, I would just use multiple smaller units readily available. Although you might need a lens or a set of mirrors if you want to use a single fiber. What about a cathode ray tube, less efficient but capable of delivering more power? Although getting some PVs to work with it could be an issue.

    BTW, mgb that is a good idea!
     
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