Rheostat as 6volt dimmer switch

Discussion in 'General Electronics Chat' started by Fisherman, Dec 10, 2007.

  1. Fisherman

    Thread Starter New Member

    Dec 10, 2007
    5
    0
    Howsit fellas,
    Wondering if you guys could point me in the right direction. I have a 6volt halogen headlight i use for fishing at night in Hawaii. Im trying to find a rheostat or pot that can be used as a inline dimmer control for the light. It runs off a 6volt 4.5amp/h rechargable battery. It took me along time to find out that its a rheostat not a dimmer knob so as you can tell im not an electrician. Ive talked to state electric or what ever they said it needs to be 27watts but i cant find one anywhere. will any rheostat rated above 27watts work or does it have to be exact. Im looking for something cheap for a homemade headlamp system. Can someone plz help. Any info you have to offer would help. Wiring Watts Volts resistance im in the dark.
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    You're not looking at small nor cheap. The control will be a large hunk of ceramic that has resistive wire wrapped around it and a wiper. It will need a box of some kind and it will get very warm. It will drain your battery just as fast as full brightness.

    The other problem you'll have is halogen's hate being dimmed and bulb life will be shortened.

    Consider getting one of the better headlights such as
    http://www.streamlight.com/product/product.aspx?pid=58
    One single LED mode it will run 150 hours, for all 7 I think it will do approx 22hrs.
    50 lumens from an LED is not the same as from a halogen or incandescent but it projects well.
    You'd have to test it in person.

    This has a zenon bulb and three LEDs, you can turn the xenon, one led or three leds on
    http://www.streamlight.com/product/product.aspx?pid=57

    They have so many... I think for what you have the zenon bulb and three LED would work and it will cost about the same as the rheostat/potentiometer.

    http://www.leedselect.com/parts-resistors.html#rheostats

    25 ohm 25 watt dual rheostat $25.00 (fing huge!)
    35 ohm 12.5 watt rheostat $10.00 (you won't have fine adjustment).
    300 ohm 300 watt Ohmite $24.00 This would give more control but is massive.

    Another source
    http://www.surplussales.com/Potentiometers/Rheostats/PotsRheost-3.html

    If battery life isn't a concern you could make blockers similar to the slits used on military vehicles.
     
  3. Fisherman

    Thread Starter New Member

    Dec 10, 2007
    5
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    Ah man the main thing would be to increase battery life. I have other headlamps with leds and such but you cant beat the 6volt halogen when fighting a big 50+lb Fish on slippery wet lava rock. Sometimes we have to shine our lights in front of the fish to turn it away from a reef. If im just tying knots or cutting bait i thought i could save battery time if i just turned down the light but apparently not. My friend has the exact same set up except his light has a built in dimmer control and says it saves him juice. It seems like it would if your only using 2volts wouldent it drain less on the battery? Sorry but im not technology ept. Plz keep the info coming how much resistance do i have do i need. Is there anything i could use that would increase battery life and act as a dimmer? All info helps. Can i switch to a 6volt xenon bulb to increase bulb life, is there a big difference in brightness?
     
  4. Fisherman

    Thread Starter New Member

    Dec 10, 2007
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    0
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    They've been smokin' the paca-lolo, Bra! They multiplied 6v by 4.5 Amp Hours and got a good buzz!

    The current value we really need to know about is the headlamp. If you know how many watts the bulb is rated for, you can divide that by 6 to get the current it will draw. (Current = Power / Voltage) For example, if the bulb is rated for 6V & 15 Watt, it will draw 15/6 = 2.5 Amps. A ten watt bulb would draw only 1.7 A.

    Whatever amperage is drawn by the bulb will also go through the windings of the potentiometer. That current, whatever it is, gets squared and then multiplied by the full value of the pot to determine power dissapated. If the number is equal to or lower than the potentiometer Watt rating, the pot will work fine.

    So... the watt rating needed for the pot will depend on the resistance of the pot and the wattage of the bulb.
     
  6. Fisherman

    Thread Starter New Member

    Dec 10, 2007
    5
    0
    Ho thingmaker sounds like you one local braddah, the paca-lolo has got my brain all twisted with all this electronics stuff. Its a phillips 4w 6v = .66 amps so if i got a 5w pot it would work? How many Ohms? They said it would have to be a rheostat so this is false. Would it save battery life? Just two wire pot? + in + out? Thanks for the info Thing braddah man.
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I'm haole, no kama'aina, but I did spend four years guarding Pearl Harbor from scantily clad tourist women and their daughters. :D

    If you can find a 20 Ohm 10 Watt potentiometer, it will work. So will a 50 Ohm 25 Watt pot. So will any pot with Watts / Ohms equal 0.45 or more. (.67 *.67 = .45)
     
  8. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Pulse with modulation (PWM) could be an alternative to your rheostat. A 27W rheostat is not cheap and also dissipates energy (it is not economic either).
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I don't think anyone even makes a "27 Watt" piece. 25, sure. 30, sure. But 27?

    The PWM control would be ideal, but would require correctly laying out some components and then soldering them. Would you be up for such a thing, Fisherman?
     
  10. Fisherman

    Thread Starter New Member

    Dec 10, 2007
    5
    0
    Ho man im glad im a plumber......Na not looking at making such a big ordeal out of it. I thought i could just get a dimmer hook um up and save some juice but oh well. TerryKing as you mentioned about the weaker light thats what ive been doing. I just have a Ravoc Led headlight that i use to open beers with. When you wake up in the middle of the night to a reel rachet screaming you dont want to have to sort through your lighting situation you want your light ready to go. Thanks for all the replys if anyone else has ideas let um be know.
     
  11. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    You open beers with your flashlight? Poor flashlight! :D

    I prefer using my teeth (but then again I don't drink beer). :D:D:D
     
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