Portable UV Water Purifier

Discussion in 'The Projects Forum' started by ddcc, Apr 28, 2011.

  1. ddcc

    ddcc Thread Starter New Member

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    I'm currently working on a portable UV water purification project, but am having a little trouble with the UV emission. I've looked into possibly using an ultraviolet LED array, but the problem with this is that most UV LEDs emit the wrong frequency of UV to be germicidal (~400nm, instead of ~250nm). UV fluorescent germicidal bulbs do work, but they require AC power and an additional ballast for constant current, which would require an inverter and controller circuity. Unfortunately, since I'm looking to power this project off of solar cells, I'm trying to keep the excess circuitry to a minimum. Does anyone have any suggestions?
  2. marshallf3

    marshallf3 Well-Known Member

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    You're pretty much out of luck, the only decent way to create the proper wavelength of light for germicidal capability is by using a germicidal lamp tube or a laser that operates in that region.

    If you can find a very small germicidal lamp tube making a driver circuit to run it off of battery power is easy, matter of fact I've seen entire circuits sold on Goldmine ready to hook up to a tube. One could also salvage the driver circuit out of a fluorescent camping lantern or anything else that runs those little tubes.
  3. ddcc

    ddcc Thread Starter New Member

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    Since the ballast is just maintaining a constant current despite the decrease in resistivity, would an LED driver work as a substitute, provided that the output voltage was correct?
  4. marshallf3

    marshallf3 Well-Known Member

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    Nope, fluorescent tubes need a HV pulse to start ionization of the internal gas then they're current limited to the proper mA for the bulb size, however the voltage across them is still around 85V or whatever it ends up needing to be to maintain the proper current.
  5. Kermit2

    Kermit2 Well-Known Member

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  6. John P

    John P Senior Member

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  7. ddcc

    ddcc Thread Starter New Member

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    Although the UV LED's look pretty good, the $300 minimum order is wayyy out of my budget. It looks like the SteriPen does use a regular mercury discharge bulb, located within a quartz sleeve to prevent water contamination if the bulb breaks. The only details that I could find on the electronics are: "SteriPEN uses a fairly straight forward electronic ballast - essentially a Royer Oscillator. The input is nominally 5 Watts with an output of approximately 350VAC RMS @ 40kHz. SteriPEN's electronics are what is termed a regulated power supply. This means that the lamp always gets the same voltage and current or none at all. This means that the lamp will provide the same dose each time rather than going dimmer as a flashlight does when the batteries discharge."
  8. BillO

    BillO Well-Known Member

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    I think this thread should be closed. If we advise on this and the water purification fails and the OP dies of dysentery, won't AAC get sued?
  9. Kermit2

    Kermit2 Well-Known Member

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    I believe the onus for 'proving' the proper and safe function of any electronic device is on the person who designs and builds it, not with the party who 'has an idea or suggestion' to give.
  10. BillO

    BillO Well-Known Member

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    I agree with you. Others, not so much.

    Sorry to the OP for the hijack.
  11. ddcc

    ddcc Thread Starter New Member

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    BillO: You have a valid point; I plan on testing the UV water purifier with some biological test kits to make sure that it's actually effective.

    I saw the 12V tube driver board up on Goldmine, but it seems to be designed for smaller germicidal tubes (around 6", assuming that their "super blacklight" uses this board). Also, the one minute cooling time is a significant issue, since I'm evaluating the effectiveness of UV purification for rural water supply in third world countries without an electrical grid. At the moment, I think I'm going to get a G8T5 bulb with a 12V ballast (pn# 2D12-1-9), and see how well it works.
  12. ddcc

    ddcc Thread Starter New Member

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    I received all my components today, and put everything together for a quick test (~5sec). The entire assembly turns on, and I see a dim blue light coming out of the corner of the box, but the power supply indicates that only .15A is being drawn at 12V, which doesn't match up with the 8W rating of the tube.

    Attached Files:

  13. ddcc

    ddcc Thread Starter New Member

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    Fixed the issue with the ballast; now it's drawing ~0.7A @ 12V, which is correct. Some more pictures.

    Attached Files:

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