Very Simple Steady 5v from a 9v needed..

Discussion in 'The Projects Forum' started by SoBeJohn, Apr 18, 2011.

  1. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    I'm heavily involved with Paintball. One of the major drawbacks is that goggles tend to fog up. I've been playing around with computer mini fans for a while, and have gotten close but still no cigar.. I'm currently using 2-5vdc mini fans, in series..( both wont always turn on when in parallel),with a draw of .8W..I use a 9v battery, have been playing and alternating with resistors between 1/2W up to 2 W and between 18 to 22 Ohms.. its obvious they heat up but not enough to be a significant hazard.. I do notice that there is alot of current fluctuation and I feel this may be due to the heat of the resistor. Or please correct me if I am wrong.. I'd like to design a very simple resistive capacitive ckt,as to prolong a steady current draw..I can get the fans to work as low as 4 V and that would get me a longer run time.. When the Current starts to vary, the fans become rather annoying..
    I need to keep this very simple since its being mounted on goggles.. I appreciate all your help in helping me get this figured out.. Again, thanks in advance.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    The simplest solution is to use a low drop out (LDO) linear voltage regulator. However, a simple solution is not always the best. Linear regulators are very inefficient. It will keep the voltage across the fans constant but the total power dissipation will be the same. Since you need to have longer battery life, a switching buck regulator is a better choice. It is slightly more complicated to build it but it has much better efficiency, hence, less power wasted as heat.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Your root problem here is the 9v battery. They don't have much capacity and sag a lot as they drain. You might get better results overall from two AAs but of course your current fans may not work at 2-3v. There are motors for that low voltage.

    I'm not sure what you're needing. What happens if you just put your two fans in series with the battery? Does it "sag" too much? You could easily use a 7805 voltage regulator to hold the voltage to the fans constant for a while, but the bad part of this strategy is that a lot of the power consumed is wasted as heat by the regulator, just like your resistors. But you would have constant voltage until the battery goes below 6.5v or so.
     
  4. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    I've used 2 AA and 3 AA battery packs. and I understand what you're saying and agree I will get more life out of the AA's. I think the biggest drawback here is size and efficiency.. Please take into consideration that the fans and battery packs are mounted right to the googles with the batterypack attached to the elastic strap with a velcro strap for easy access. the battery pack/holder I am using have an incorporated on/off switch.., so size is a major issue here..I'm open to suggestions but I need to stay away from bulkyness.. How big is this 7805 ckt board?(link?)
     
  5. wayneh

    Expert

    Sep 9, 2010
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    The 7805 actually just a 3-pin component; in (9v), ground, and out (5v). It's in the same package used for medium power transistors. So it's perfect for a low space solution. It's used in tons of DIY circuits because it can be wired inline as just a fat spot in the wire, converting almost any DC voltage to a nice steady 5v. Just Google for the datasheet.

    Given your 9v source and its limitations, consider the low-dropout version suggested by mik3. It's harder to find and probably a bit more expensive but will squeeze an extra volt or so out of the 9v.
     
  6. someonesdad

    Senior Member

    Jul 7, 2009
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    Have you tried putting a coating on the inside surface of the goggles to reduce condensation? 25-30 years ago I did a goodly amount of cross-country skiing and fogging of goggles was a pretty common problem. IIRC, I found a small bottle of some liquid that was rubbed on the inside of the goggles and it helped a lot in reducing condensation. Sorry, I can't remember the product name, but I think it was silicone-based. You might also try Rain-X, as it's probably available in any auto supply store. An old standby is to rub a small amount of dishwashing liquid onto the goggle's surface.
     
  7. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    wow, that would be great.. let me look into this and see where I can get both.. I'm willing to try them both and get this working.. Any suggestions as to where I can find them?Thanks..
     
  8. wayneh

    Expert

    Sep 9, 2010
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    You can find the 7805 at your local Radio Shack, or from many junked circuit boards if you're so inclined. Mail-order places such as Mouser or DigiKey will have everything.

    I'd recommend trying the 7805 approach to see how it works for you. If it works well, you can later gain the incremental improvement from the LDO version.
     
  9. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    ok i found the 7805, do you guys suggest I get a Capacitor? and if so, what Voltage and μF value..
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    If you run the fans at 5V what will be the current?

    Just to see if it is worth to buy a switching regulator.
     
  11. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Consider making up a battery pack using AAA cells. They may be the best compromise between size and weight.
     
  12. mik3

    Senior Member

    Feb 4, 2008
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    LiPO batteries offer very good capacity at small size and weight but they are quite expensive.
     
  13. Jeff7

    New Member

    Apr 17, 2011
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    You could even be ok just running a little 12V fan right off of 9V.
    This would depend on the fan itself; some are more tolerant of undervoltage than others.

    Or get a little switching regulator, like this little thing.
    6.5-34Vin, 5V out, and reasonably efficient.

    What's the current draw on the fan you're looking to use?
     
  14. wayneh

    Expert

    Sep 9, 2010
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    Normally yes, follow the datasheet recommendations. But for this usage, I don't think it's much of a concern. The battery is a much larger "capacitor" than the recommended one for the input. And the motor won't care if the output is a little noisy. Someone may jump in to correct me, but I don't think it will use any more power or perform poorly by leaving off all the caps.
     
  15. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    the fans run at +/- .8w, I will be using 2 fans...will run them in parallel. i dont recall getting them to work in series..

    I live relatively close to an electronics components house, i'm going to pick up both the 7805 and LDO tomorrow and get to work on this.. i'll keep you guys posted how it goes, using both, a 9V and a 3 AA pack..I think i'll get the longer run time from the 3 AA's, but i'll put it to the test..
     
  16. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    it says +/- .8W, I am using 2 fans in parallel.. i'm looking around in mouser, but these recom parts are really going to kick up my costs..
     
  17. Jeff7

    New Member

    Apr 17, 2011
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    Ooo.....how much runtime are you looking to get? A 9V won't be able to power two of those things for a very long time. If you're going to be using something like a voltage regulator, that might end up reducing the overall life of a NiMH 9V, as it'll be able to discharge it rather deeply (<1V per cell).

    Is the antifog coating an option, as Someonesdad suggested? If the fans you're putting in aren't vented to the outside, you may well just end up recirculating humid air, and it could still cause fogging anyway. I believe RainX does make something specifically to reduce fogging.
     
  18. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    Naah, that stuff doesnt really work for a long time... there are many products available, there's even double pane thermal lenses.. but you still get some fogging, specially with all the humidity down here in Florida.. the best thing is to have small fans.. to keep air moving.. I personally like both fans blowing air in.. some guys use one fan in/ one fan out.. I just want to perfect the battery efficiency issue and sell them.. I've been playing paintball for a good 25+ years.. but thanks for your input..
     
  19. SoBeJohn

    Thread Starter New Member

    Apr 18, 2011
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    I've tried various fans.. in both 5v and 12v operating values, also tested with 2AA's, 3 AA's and 9V battery packs.. so far the most efficient, longer lasting setup is 2 12v fans in parallel with a 9v battery, and the run time is 6 hours.. but i'm into looking at different current and rpm value fans. to achieve longer, more efficient run times..

    As for the goggles, they are all vented at the top, to allow for air to circulate and even with the fans, there is enough vents for air to escape. they arent sealed as with ski goggles..I'll try to provide some pics here shortly of fan setups I have created.. in various different paintball goggles..

    Antifog, is NOT the solution..
     
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