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Thread: I'm a newb and I need some clarification

  1. #1
    Unenlightened
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    Oct 2018
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    Default I'm a newb and I need some clarification

    I'm totally new to lights. I have a basic knowledge of electronics and electrical circuits and have some experience with wiring and tinkering. I also have a decent understanding of Li-ion cells and wiring battery packs (I am currently powering my living space with 2 48v Li-ion packs that I made).

    I want to build my first dive light. I never enter overhead environments and I still don't dive at night, but the water in my area usually has low vis and I want to start bringing a light with me (to recreational depths). I bought The Dive Light Companion and it is a really cool book, but it barely has any info on LED lights. I've spent some time over the last few days reading here on the forum and watching YouTube videos trying to learn what I can about LED flashlights. With the info about building lights from PVC in TDLC and the info I have gathered reading and watching videos I think I have most of the knowledge I need to start making my first light. I am not looking to make anything that will last forever or anything that will impress anyone with how pretty it is. I just want to make a light the gives a decent amount of light and that will give me some hands on experience building these things. Later down the road I can get more advanced and detail oriented.

    I think I found a good LED/driver combo. Will these work together? https://www.lightmalls.com/20mm-cree...mm-copper-base https://www.lightmalls.com/6-9v-5a-5...hp5-mtg2-xhp70
    Then I could use 3 18650's in series and instead of wiring together a pack and shrink wrapping it I could just have them stacked inline in a holder or something along the light for easy removal and charging. If this woudn't be a good choice could someone please give me some suggestions? Is this website a decent one to order these parts from?

    On another note I don't understand something (possibly many things) about how drivers work. Specifically with a reed switch. If an LED has 5 modes and you use a 5 mode driver, how do you activate the different modes with a reed switch? Is it something where every time you cycle power it goes through a different mode? Also, what should one look for in a reed switch? They all seem to be low voltage switched that I see for sale, but I haven't found one that states what that voltage is.

    Anyway I'm sure I've left some questions out, but my head is spinning just a tad from all of the different information I have been trying to absorb. I am hoping that this combo will be enough for me to throw together a light to get me started down the path of light building. Thanks for reading and responding.

  2. #2
    Flashaholic* DIWdiver's Avatar
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    Default Re: I'm a newb and I need some clarification

    First of all, welcome to the forum!

    It sounds like you have made a pretty good start on learning what you need to know. The components you selected should work well together. Maybe I can clarify a few things.

    From an electronics point of view, the light you are talking about comprises 5 basic elements: LED, driver, controller, battery, and switch. Quite often the driver and controller are integrated onto a single PC board, which is called a driver.

    The LED converts current to light (and heat).
    The driver controls the current to the LED.
    The controller tells the driver when to turn on and off, and in rare cases, how much current to supply to the LED.
    It's pretty obvious what the battery and switch do.

    All modes are generated in the controller. In the strictest sense, a driver doesn't have modes; a driver with modes is really a driver and controller integrated. An LED never has modes. It's obvious how flashing, pulsing, or SOS signals are produced by the controller, but dimming is also normally done by the controller switching the driver on and off.

    There are two ways that switches are used to control modes. By far the most common in inexpensive hand-held lights is that the switch directly controls the power from the battery to the controller and driver. While the driver immediately shuts off when power is removed, the controller continues to operate for a short time. If you turn the switch back on while the controller is still running, it can tell what you did and switch to the next mode. If you leave the switch off until the driver shuts down (typically around a second), when you turn it back on the controller may or may not remember the last mode you set, depending on the controller. If not, it will come up in the standard power-up mode. Some controllers can distinguish between long and short presses, and can use sequences of long and short presses to perform more complex functions like enabling different features, changing mode sets, etc.

    The other way is that the controller is always powered, or perhaps has a separate power switch. Some advantages of this method are that the switch doesn't have to be able to carry the main power, and you can now also detect very long presses.

    Now about reed switches. The VAST majority are designed for low currents. Some are rated below 100 mA, and very few are rated over 1000 mA. The highest I've seen is 3A. As for voltage, some are rated 6V, some 24V, but many are available at 100V or above. Your best bet is to use them below 100 mA, 24 V, or to find one with ratings. The large on-line electronics distributors usually have ratings and datasheets for most component they sell.

    If you want to use a reed switch to control currents above 1A, I would recommend using a FET in conjunction. There is a lot of discussion here and elsewhere about how to do this.

  3. #3
    Unenlightened
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    Default Re: I'm a newb and I need some clarification

    Great, thanks for the response. I ordered a different LED driver/controller than the one I linked. I also found some heavy duty reed switches rated for 3A. The components I ordered will draw a max of 2400ma so I should be able to wire the switch directly between the 18650 and the driver, right?

  4. #4
    Flashaholic* DIWdiver's Avatar
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    Default Re: I'm a newb and I need some clarification

    In theory, that should work. There could be some gotchas, especially if the vendors are playing specsmanship. Many components have specs that while real, are not achievable in real products. Do you have a spec for the switches? I'd be happy to review it.

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