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Thread: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

  1. #1
    Flashaholic* Mattaus's Avatar
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    Default Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Hey all,

    A work colleague, fully aware of my skills with building ridiculous flash lights, asked me if I could do something with his 2xAA mini-mag. Having never even held one let alone modified one I jumped at the chance. I want to go all out and have settled on a triple XP-G mod like here. I'm going to copy that build pretty much exactly, starting with powering the emitters in parallel using this driver. My question however is how much current the driver is pulling from the cells.

    Considering I plan to use 2 series connected protected 14500 cells the current draw can't be very high. Am I right in reading the table provided on the drivers sale page that states that with 7.2V input, the driver will only draw 0.17A, 0.85A and 1.6A from the cells to provide it's 0.25A, 1.38A and 2.8A output current? 7.2V in is a lot when you consider I only need about 3.15V across each emitter. Being that that are in parallel we're looking at 1W, 5.5W and 11.3W of heat for each drive level! That's a lot of heat in such a small package...

    Is my maths correct? Does the driver function as I expect?

    I can't really think of any other driver to use as the 14500 cells are pretty limiting. Any suggestions!?

    Thanks,

    - Matt

  2. #2
    Flashaholic Ogg Vorbis's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    The circuit works as a buck driver (reduces the voltage) so the input of 7.2V at 1.6A , is stepped down to give 3A output at around 3V (the LED Vf).
    So you are right there.

    This means you connect the LED's in parallel, the voltage will still be 3V, but the current is divided by 3, i.e. each LED should get about 1A each.

    As for the power and heat, Power in is 7.2V * 1.6A = 11.3W
    Power out on high, assuming 90% efficiency is ~10.3W

    This means 1W is lost at heat in the driver (you need to heatsink the large black chip on the topside of the driver)
    And then 10.3W is going to the LED's, so it will get hot!

    I have used the same driver in a Mag 2C mod driving a SSC P7, it got warm but handled the heat fairly well.
    I know there are a few other drivers out there that will give the same output etc, but i've never used them... they also look a tad taller.

    - Dan

  3. #3
    Flashaholic* mvyrmnd's Avatar
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    Default

    If you're supplying 3.15V and 2.8A (3 emitters seeing 933mA each) then you're using 8.82W.

    This means the current draw from the batteries at their nominal voltage would be 1.22A on high.

  4. #4
    Flashaholic Ogg Vorbis's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by mvyrmnd View Post
    If you're supplying 3.15V and 2.8A (3 emitters seeing 933mA each) then you're using 8.82W.

    This means the current draw from the batteries at their nominal voltage would be 1.22A on high.
    Your calculation assumes a 100% efficient driver. Current draw from the batteries will be slightly higher due to the inefficiency of the driver.

    The measured 1.6A from the tail is realistic.

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    Flashaholic* Mattaus's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Ah OK so the driver's current draw from the batteries is correct and within spec of the cells? That was my main concern. I did explain to the guy I'm building it for that he can't expect to run it on high for very long at all. Better start working on that heat sink....

  6. #6
    Flashaholic* mvyrmnd's Avatar
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    Quote Originally Posted by Ogg Vorbis View Post
    Your calculation assumes a 100% efficient driver. Current draw from the batteries will be slightly higher due to the inefficiency of the driver.

    The measured 1.6A from the tail is realistic.
    I realised that as soon as I posted it, but the site went down for the backup and I couldn't get back to fix it!

  7. #7
    Flashaholic* mvyrmnd's Avatar
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    Quote Originally Posted by Mattaus View Post
    Ah OK so the driver's current draw from the batteries is correct and within spec of the cells? That was my main concern. I did explain to the guy I'm building it for that he can't expect to run it on high for very long at all. Better start working on that heat sink....
    AW 14500's are labelled 900mAH, and usually measure pretty close to that. Being LiCo cells, the max safe discharge rate is 2C, meaning 1.8A.

    If you're going to be pulling 1.6A, make sure you have good cells - that sort of current draw will be too high for cheap cells.

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    Moderator Kestrel's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    If LiCo 14500's are going to be a limiting factor for safe operation, what about AW IMR 14500's? They are rated for 4 amps continuous discharge.
    Last edited by Kestrel; 04-23-2012 at 04:53 PM.
    In the past we have had a light which flickered, in the present we have a light which flames, and in the future there will be a light which shines over all the land and sea.
    - Winston Churchill

  9. #9
    Flashaholic* Mattaus's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by Kestrel View Post
    If LiCo 14500's are going to be a limiting factor for safe operation, what about AW IMR 14500's? They are rated for 4 amps continuous discharge.
    mvyrmnd has made the same observation. The guy I'm basing my build on used trustfire flame cells and seemed to have no problems. I'll see how they handle and if I feel they get too hot I'll recommend a set of IMR AW cells.

  10. #10
    Moderator Kestrel's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    mvyrmnd posted about LiCo's, I'm suggesting IMR's - both AW but very different chemistry: IMR's are far better for high discharge applications.
    I guess you're feeling lucky about going with Trustfires then.
    Last edited by Kestrel; 04-23-2012 at 06:52 PM.
    In the past we have had a light which flickered, in the present we have a light which flames, and in the future there will be a light which shines over all the land and sea.
    - Winston Churchill

  11. #11
    Flashaholic* Mattaus's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by Kestrel View Post
    mvyrmnd posted about LiCo's, I'm suggesting IMR's - both AW but very different chemistry: IMR's are far better for high discharge applications.
    I guess you're feeling lucky about going with Trustfires then.
    Sorry I got myself confused with the battery chemistry's. I'm still learning.

    As for the Trustfires...I live on the edge lol. I think i'll get the guys light working first and then strongly recommend IMR 14500's. The Trustfires are cheap enough, just have to be careful.

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    Flashaholic* jasonck08's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by mvyrmnd View Post
    AW 14500's are labelled 900mAH, and usually measure pretty close to that. Being LiCo cells, the max safe discharge rate is 2C, meaning 1.8A.

    If you're going to be pulling 1.6A, make sure you have good cells - that sort of current draw will be too high for cheap cells.
    Not sure where you got the 900mAH figure from. The ones I've seen available from AW are 750mAH...

  13. #13
    Flashaholic* mvyrmnd's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by jasonck08 View Post
    Not sure where you got the 900mAH figure from. The ones I've seen available from AW are 750mAH...
    You are entirely correct! This is what I get for posting before coffee.

    Please ignore all of my advice in the thread :P

  14. #14
    Flashaholic* Techjunkie's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    I think that driver is bigger than you realize. Are you sure it will fit in the 2AA light?

  15. #15
    Flashaholic* Mattaus's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    QUOTE=Techjunkie;3932953]I think that driver is bigger than you realize. Are you sure it will fit in the 2AA light?[/QUOTE]

    Hmmm well the site says 17mm - and that will fit in the head of the light which is where I intend on using it. If not I'm sure I can find another application for it :-)

  16. #16
    Flashaholic* Techjunkie's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by Mattaus View Post
    Quote Originally Posted by Techjunkie View Post
    I think that driver is bigger than you realize. Are you sure it will fit in the 2AA light?
    Hmmm well the site says 17mm - and that will fit in the head of the light which is where I intend on using it. If not I'm sure I can find another application for it :-)
    Wow, I completely missed that. I think this is the first inexpensive 3A buck driver I've heard of this size. Please let us know your impressions of it and if a standard 16.8mm driver pill can accept one with little trimming.

    Oh, wait, check out the user comment with the subject "size"... on 4/16/2012 someone reported: I just got one and it's 19(mm)....not what I was expecting..

  17. #17
    Flashaholic* Mattaus's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Yeah it is confusing because the sales text says it's 17mm from the 28th of August (no year, but you'd assume they meant at least last year) but clearly 19mm drivers are shipping out to customers.

    I'm still going to use this driver because 19mm will fit in the head of the mini-mag, but the pill I make will have to be a bit different from the usual. Nothing hard to do though.

  18. #18
    Enlightened
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Did you finish this project?

    Interested in the same Mini Mag with triple XP-G

  19. #19
    Flashaholic* Mattaus's Avatar
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    Default Re: Triple XP-G Mini Mag Build - Stuck already and I haven't even started.

    Quote Originally Posted by PhatPhil View Post
    Did you finish this project?

    Interested in the same Mini Mag with triple XP-G
    Not yet. I started a P60 Drop-in project and am in the midst of building and selling 30+ of them. I'm taking time out of everything else to get those done first as they are a priority.

    Once they are done though I'll be straight onto this.

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