warning about cap with built in LEDs

Discussion in 'Functional Gear & Equipment' started by QuietOne, May 7, 2009.

  1. QuietOne

    QuietOne Monkey++

    Yesterday I recommended a baseball cap with 2 built in LEDs from http://www.gofastandlight.com/default.asp as a great idea for a hands-free light. I found that the cap has a serious problem; the LEDs are severely overdriven, running at 6 volts instead of a normal 3 volts. At this voltage the LEDs will not last any longer than an incandescent bulb.

    The problem can be easily fixed. Get 2 US pennies and sand the surfaces lightly. Remove one of the 3V button cells and replace with the pennies. The light is still bright enough for walking at night and at 3V the LEDs should last about 100,000 hours.

    Overdriven LEDs are a problem with many of the cheap flashlights imported from China. They are very bright but at the cost of having the LEDs fail quickly. If you are going to depend on one of these flashlights use a multimeter to measure the voltage drop across each LED; it should not be higher than the rating for that LED, usually 3 volts.
    NotSoSneaky and D2wing like this.
  2. dragonfly

    dragonfly Monkey+++

    great info!
  3. Seawolf1090

    Seawolf1090 Retired Curmudgeonly IT Monkey Founding Member

    GASP! Those wascally Chinese! [beat]
  4. B540glenn

    B540glenn Should Be Working Founding Member

  5. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    These work pretty darn good for hands-free working. Once I break this one I need to get one of the 6 LED headlamps.
  6. eXe

    eXe Monkey++

    I have the same one, works like a charm. Really comes in handy for those times where you need both hands and cant hold a flashlight.
  7. The Expendable

    The Expendable Bread and Circus Master

    I got the following from LED Basics; gaining an understanding of how to work with LEDs. If you want more detailed info, check it out.
    The required voltage depends on the type of LED being used. You should use at least 3 volts for the lower voltage types, 4.5 volts for the 3.4 volt types, and 6 volts for the 430 NM blue.

    Is there a dropping resistor in the circuit? If so, the higher voltage is accounted for. A 3.4 volt LED with a 6 volt supply voltage leaves 2.6 volts to be dropped by the dropping resistor.

    Are the LED's in the cap wired in series or parallel? Most likely they are in series. That is the preferred method of wiring multiple LED's. You can put LEDs in series with only one resistor for the whole series string.

    Add up the voltages of all the LEDs in the series string. This should not exceed 80 percent of the supply voltage if you want good stability and predictable current consumption. The dropped voltage will then be the supply voltage minus the total voltage of the LEDs in the series string.

    Do not put LEDs in parallel with each other. Although this usually works, it is not reliable. LEDs become more conductive as they warm up, which may lead to unstable current distribution through paralleled LEDs. LEDs in parallel need their own individual dropping resistors. Series strings can be paralleled if each string has its own dropping resistor.

    OK, with all that out of the way, I personally would not modify the circuit to use less power than factory specs. It's my LED advice of the day. You can take it or leave it.
    Last edited by a moderator: Jan 15, 2015
  8. Seacowboys

    Seacowboys Senior Member Founding Member

    warning about cap with built in LEDs:
    They make you into [peep]a very good target![elim]
    oldawg likes this.
  9. The Expendable

    The Expendable Bread and Circus Master

    Mine has LED's that form an arrow, and it says "I'm with stupid" :)
  10. QuietOne

    QuietOne Monkey++

    Expendable said:
    The LEDs are the small T1 3V types. Apparently wired in parallel and no dropping resistor. Any flashlight that uses a dropping resistor is a fraud; part of the energy that should be used to generate light is being wasted as heat.
    I have 40 years of experience with electronics. These "factory specs" were set by an incompetent Chinese exporter who is only interested in ripping off foolish Americans. I really recommend that if you're getting a flashlight with LEDs and expect it to keep working long term that you make sure the voltage is right for the LEDs. It could literally mean your life if your flashlight fails.

    P.S. the cap gives plenty of light with one battery.
  11. The Expendable

    The Expendable Bread and Circus Master

    I will defer to your knowledge, but my understanding was that better to have to much power being dropped by a resistor, than exactly enough power with no resistor. If you waste energy as heat it only means shorter battery life, right? Plus, I didn't think that LED's were supposed to be wired in parallel. Doesn't that tend to generate more heat, thereby wasting even more power? Anyway, I was just throwing in my two cents worth. I doubt a burned out LED flashlight would jeopardize my life, since I would not have only one flashlight to depend on.

    I will concede that using one battery instead of two would possibly save money. My question is if one battery would last as long as two batteries?
  12. GMan

    GMan Monkey++

    And here I thought a resistor in series with an LED was intended as a current limiter.
  13. D2wing

    D2wing Monkey+

    I am afraid of electricity, I peed on an electric fence 50 years ago. Can still feel it.
  14. tedrow42

    tedrow42 Monkey+

    we use these on the boats. they last about 3 months but we use them every night.
  15. azrancher

    azrancher Monkey +++

    Last edited by a moderator: Jan 26, 2015
  16. kckndrgn

    kckndrgn Monkey+++ Moderator Emeritus Founding Member

    I've got 3 baseball caps with the LED lights. Never had a problem with the LED's burning out. All of my caps are from Bass Pro. One quit working when the dog chewed up the battery pack (nothing else on the cap, just pull off the battery pack, go figure). The second one is starting to flake out, but I know why. I wear the thing all the time, even in the summer when I sweat quite a bit. I mean, sweat to the point it's dripping off the brim of the hat. My black hat is now grey because the sweat took much of the dye out of the fabric. All that moisture has made the switch unreliable.

    My last hat is my hunting cap, blaze orange, and the 2 LEDs give just enough light to get to the stand before sunrise.

    I've got a couple of the headband style lights too, but they rarely get used. Thought about getting this lamp:
    Outdoor Waterproof 1600LM XM-L T6 LED Headlamp + 2 X 18650 Rechargeable Batteries + Charger - Cree Headlight - Amazon.com
    On another forum it has received good reviews, and I like that it's rechargable.
    Last edited by a moderator: Jan 25, 2015
  17. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Last edited: Jan 16, 2015
  18. azrancher

    azrancher Monkey +++

    Looks like an assume lamp.

    I actually found one that did flash, and SOS, it's a handheld 2-cell 18650, I think it was advertised as 1600 LM, but who really knows.
    Last edited by a moderator: Jan 25, 2015
  19. scrapman21009

    scrapman21009 Chupacabra Hunter

    My old crew used to use the on that could be white, red, or green as standard issue from the company. We would use the green light and our hands as a shutter and had our own modified morse code we would use in the tunnels as it was to loud to use radios.
    kellory likes this.
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