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Need More Power in High Mode

  • streetrodder1958 Sunday, December 16, 2012 8:55 AM Reply
    Just got my drivers hooked up and tested. They work as advertised with one exception, I'm driving 2 xm-l's with one and its at 2 amps. The second I'm driving 3 xm-l's and its at 2.2 amps. Can someone tell me which resistor I would need to change to get this up to the rated 3 amps.
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  • Janmee Monday, December 17, 2012 1:15 AM Reply
    @desolder, could you help him?
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  • desolder Top 10 Forum Poster Monday, December 17, 2012 1:44 AM Reply
    streetrodder1958 - take a look at the photo by jassius. You need to modify the sense resistor to a lower value. The existing sense resistance appears to be using two 0.22 ohm (R22) resistors in parallel, for a total of 0.11 ohm. I'm guessing the feedback voltage is 0.25V, so the current is I = V/R = 0.25 / 0.11 = 2.3A. If you want 3A, you need to lower the sense resistance to R = V/I = 0.25/3 = 0.083 ohm. One way to do this is to piggyback three 1 ohm resistors on top of the existing resistors.


    http://m2.dealextreme.com/upload/reviewpicture/201211/77746829-c1e2-42fa-a1a3-8d982640ae1e.jpg
    img src: http://m2.dealextreme.com/upload/reviewpicture/201211/77746829-c1e2-42fa-a1a3-8d982640ae1e.jpg



    What's up with the scrubbed LED driver IC markings?
    What are they trying to hide?

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    post edited by desolder on 12/17/2012 at 1:47 AM
  • Janmee Monday, December 17, 2012 1:47 AM Reply
    Thanks for your answer, you are professional man!
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  • desolder Top 10 Forum Poster Monday, December 17, 2012 1:25 PM Reply
    You're welcome Janmee :)

    After I posted that, I noticed that the resistors actually look like 0.27 in parallel with 0.22. This gives us a slightly higher resistance of 0.121 ohm, resulting in slightly lower current of 2.06A. To increase it to 3A, you want to add four 1 ohm resistors in parallel with the existing resistors (or a single 0.25 ohm resistor if you can find one).
    What's up with the scrubbed LED driver IC markings?
    What are they trying to hide?

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    post edited by desolder on 12/17/2012 at 1:28 PM
  • streetrodder1958 Tuesday, December 18, 2012 12:35 AM Reply
    Hey I just took a quick look at that pic and the first thing I see is the mode chip is gone. Will that mod with the jumper do away with the other two modes? (hope hope)
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  • desolder Top 10 Forum Poster Tuesday, December 18, 2012 1:20 AM Reply
    Yes it will. Jassius mentioned in his review that he took out the microcontroller IC in order to make it into a single mode.

    Also, his third photo appears to show another resistor underneath the 0.22 ohm resistor. He mentioned that his driver is outputting 2.6A, so you may only need to add one or two 1 ohm resistors on top in order to get up to 3A. You'll have to experiment a bit.
    What's up with the scrubbed LED driver IC markings?
    What are they trying to hide?

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    post edited by desolder on 12/18/2012 at 1:24 AM
  • streetrodder1958 Tuesday, December 18, 2012 1:27 AM Reply
    You guys are my new Heros. Just got off the {REMOVED} site from ordering the .25 ohm smd resistors so I guess while waiting for them I'll pull the chip off my boards. Thank you all so much and have a MERRY CHRISTMAS.
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    mod edited by cyclist on 12/26/2012 at 3:53 PM
  • adlamb Monday, December 31, 2012 4:14 AM Reply
    anyone got an update on this i.e. what combination of resistors seems to work best?
    I'm thinking of ripping the chip out to make it single mode and also try and squeeze a few more mA out of it as well (driving 3 x XML from 4 x 18650 )
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  • jbrols Friday, April 26, 2013 6:05 AM Reply
    @desolder
    Sorry to disturb, but could you or anyone else tell me, please, how much of a visible light output difference would it make for a XM-L LED, if current increased from 2.5A to 3.0A? Is it even worth trying to add those extra current sensing resistors, or will it only lead to empty batteries with no real light boost?
    I'm building some throwers with 75mm (actually 78mm) lenses for a friend, and it would be nice, if these throwers were GOOD throwers. I have one built for myself with the now sold out version of this driver SKU: 57779, and it gives 2.45A to the led, measured with DMM with thick wires.

    I know, I could just test the light difference for various currents, but I kinda don't have a stable variable power supply :(

    Thank you
    I'm not often right, but I've never been wrong ;)
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