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Thread: 2 LED Driver Boards in a Row ?

  1. #1
    Flashaholic J.D.'s Avatar
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    Help 2 LED Driver Boards in a Row ?

    hm,
    i wondering if it is possible to connect 2 LED Driver Boards (for example some DX boards) in a row ?

    My problem is, i have 8.4v input and each Driver only supports 6v..
    if i connect the drivers like this:

    ______________
    |_____________|
    |_____________|
    | ____________X Board 1
    = 8.4v________|
    | ____________X Board 2
    |_____________|
    |____________ |

    Do they act like a voltage divider ?
    so every board should get around 4,2v
    are my thoughts correct ?

    thanks
    Last edited by J.D.; 01-04-2008 at 07:59 AM. Reason: typo

  2. #2
    *Flashaholic* Illum's Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    from what it sounds like it may work, but the moment one boards load opens up [often accidentally if your load burns out] you will fry the other board
    I'd much rather prefer them connected in parallel and some kind of step down DC-DC regulator that can provide the more current than your boards need
    Last edited by Illum; 12-29-2007 at 10:08 AM.

  3. #3
    Flashaholic J.D.'s Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    i think it´s worth a try
    thanks for the open load reference.

  4. #4
    Flashaholic* TorchBoy's Avatar
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    Default 2 LED driver boards(?) in a row

    You don't actually give an example of any of the DX boards, so I can only guess which you might be thinking of using. If it's a 3xAMC7135 board then you can simply use a diode to drop the voltage the board gets to under 6V. Normal diodes drop about 0.6V but there are diodes that drop about 3.6V across them at 1 amp, and what's more they even emit some light while doing it. (Namely, a Cree XR-E.) The AMC7135 only uses a couple of hundred microamps for the reference terminal so the LED it's driving will get almost exactly the same as the other LED.

    In other words, I don't think connecting two boards in series is worth trying because there's no point.
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  5. #5
    Flashaholic J.D.'s Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    @TorchBoy
    you´re right - i thoungt about the 3x 3xAMC7135 Boards. (multi level)
    My Plan is to use 4 of them to drive a 4x XR-E light - with 2x 18650 in a row.

    if i use a normal diode (or multible), want it kill the effectiveness ?

    to use a xr-e to drop the voltage sounds interesting, but i think i didn´t understand the wiring you ment ...

    can you exlain how to use the led to drop the voltage ?

    Thanks so far...

  6. #6
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    Default

    multiemitter always in series,
    drive it with a step-up driver, when You want to power them with two 18650s.

    That way all the led see the same current, switching is easier, less to goo , ...

  7. #7
    Flashaholic* TorchBoy's Avatar
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    Default 2 LED driver boards, each in series with another LED, in parallel

    Quote Originally Posted by J.D. View Post
    @TorchBoy
    you´re right - i thoungt about the 3x 3xAMC7135 Boards. (multi level)
    My Plan is to use 4 of them to drive a 4x XR-E light - with 2x 18650 in a row.
    OK. Should work well with just two of those boards, and your switch should only have to handle ~0.4mA. How's that?

    Quote Originally Posted by J.D. View Post
    if i use a normal diode (or multible), want it kill the effectiveness ?
    It would, because you'd be getting no return (light output) for the volts dropped. But using an LED instead won't kill the effectiveness because you'll drop the necessary volts and you'll get the extra light you want. The arrangement will also save some voltage, because the AMC7135 has at least 0.12V dropout, so it'll be slightly better than using two boards in series as the battery goes flat. It also means that just one board will be doing the mode control for the two LEDs in series, which might be a good thing, depending on how well they worked together (if they worked together).

    Quote Originally Posted by J.D. View Post
    to use a xr-e to drop the voltage sounds interesting, but i think i didn´t understand the wiring you ment ...

    can you exlain how to use the led to drop the voltage ?
    Simply insert it between the battery and the board, where you would put a switch if you wanted to completely turn off the current, so that all the current flowing around the circuit goes through it. It doesn't matter whether you attach it to the positive side or the negative side of the board.

    Quote Originally Posted by yellow View Post
    multiemitter always in series,
    drive it with a step-up driver, when You want to power them with two 18650s.
    It's not essential at all. As long as you're not going to get in to a current-hogging situation by having one driver feeding multiple LEDs in parallel, it more depends on what driver you have available (for what price), and what features you want in a driver. In this case the multimode board is quite attractive. But feel free to suggest drivers that you think would be suitable. They may be more suitable than my suggestion.

    Quote Originally Posted by yellow View Post
    That way all the led see the same current, switching is easier, less to goo , ...
    As I said, the difference in current between the two LEDs will be 0.2mA, and in a 4 LED light, if one board unexpectedly dies you will still have the other, still running two LEDs.

    One other advantage of doing it this way is that to turn on the light you only need to switch the set pins of the two boards, which means you're switching a total of 0.4mA, which means it's basically acting like a linearly regulating relay - very clever. You'd need a double pole switch if you wanted to keep them separate, but my first thought is that wouldn't be necessary, just take the positive feed from one of the uphill LEDs only.

    Happy new year.
    No, a torch does not always mean flames.
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  8. #8
    Flashaholic J.D.'s Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    @all
    HAPPY NEW YEAR or as we say here in bavaria "a gsunds neues"

    @ TorchBoy
    Thank you very much ! you helped me allot.
    I´ll try this wiring, the boards are ordered one week ago, i think another 2 weeks and i should receive it .
    As said, i´ll try the wiring immediately, and report it here ...

    @ Illum_the_nation - also thanks for your opinion.
    my thoughts for a multi board solution where:
    1. the costs - this AMC7135 Boards are quit cheap and i think quite effective
    2. the redundancy - if one board dies i still have backup.
    and as torchboy said if i have 20mA difference with 4 leds, thats a number i can live with.

    If the multiboard solution fails, i think i have to go with the shark...

  9. #9
    Flashaholic* TorchBoy's Avatar
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    Default LED drivers

    Quote Originally Posted by J.D. View Post
    if one board dies i still have backup.
    and as torchboy said if i have 20mA difference with 4 leds, thats a number i can live with.
    The two boards might possibly differ by 20mA due to manufacturing variation of the AMC7135s, but the two LEDs controlled by each board will have well under a milliamp difference.

    Quote Originally Posted by J.D. View Post
    If the multiboard solution fails, i think i have to go with the shark...
    With Remora?
    Last edited by TorchBoy; 01-01-2008 at 06:50 PM.
    No, a torch does not always mean flames.
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  10. #10

    Default Re: 2 LED Driver Borars in a Row ?

    Quote Originally Posted by J.D. View Post
    hm,
    i wondering if it is possible to connect 2 LED Driver Boards (for example some DX boards) in a row ?

    My problem is, i have 8.4v input and each Driver only supports 6v..
    if i connect the drivers like this:

    ______________
    |_____________|
    |_____________|
    | ____________X Board 1
    = 8.4v________|
    | ____________X Board 2
    |_____________|
    |____________ |

    Do they act like a voltage divider ?
    so every board should get around 4,2v
    are my thoughts correct ?

    thanks
    You can easily check to see if your boards need a load to keep from burning out. If they dont this arrangement should be fine.

    Also, why not try to get a parallel arrangement of your batteries to get 4.2 instead of 8.4 volts? Im assuming you have 2 nominal 4.2 volt batteries (lithium rechargeables)
    edit: just find a way to connect your 18650's in parallel and you have solved the problem.

    But, to connect an led in series between the batteries and the boards will likely burn it out due to excessive current flow.
    Last edited by rhuck60; 01-01-2008 at 05:43 PM.

  11. #11
    Flashaholic* TorchBoy's Avatar
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    Default LEDS in series

    Quote Originally Posted by rhuck60 View Post
    edit: just find a way to connect your 18650's in parallel and you have solved the problem.
    Sounds good. There'll only be 0.12V difference between that and my suggestion, and that'll only matter when the cells are heading toward discharged.

    Quote Originally Posted by rhuck60 View Post
    But, to connect an led in series between the batteries and the boards will likely burn it out due to excessive current flow.
    Why? The board has a maximum of 1 amp draw when on high mode. If the extra LED is in series that current will be going through that LED too.
    No, a torch does not always mean flames.
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  12. #12

    Default Re: 2 LED Driver Borars in a Row ?

    Since no one has yet said so in this thread, I'd like the opportunity to say that

    NO

    you cannot put two driver boards in series and feed them double their speced voltage. You'll fry them.

  13. #13
    Flashaholic* download's Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    In the real world, I am using the similar setting for a while, it works!
    My setting is 3x 18650 serial to 3x AMC7135 board serial.
    One of the AMC7135 is multi-level, so I can control the level too.
    I don't know the efficient or not, but sure it is a cheaper solution for multi-level.

  14. #14

    Default Re: 2 LED Driver Borars in a Row ?

    Quote Originally Posted by download View Post
    In the real world, I am using the similar setting for a while, it works!
    My setting is 3x 18650 serial to 3x AMC7135 board serial.
    One of the AMC7135 is multi-level, so I can control the level too.
    I don't know the efficient or not, but sure it is a cheaper solution for multi-level.
    Interesting. Have you tried doubling up the multi-level AMC7135s or any other more complicated boards?

  15. #15
    Flashaholic J.D.'s Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    @Torchboy
    yes Shark + Remora is the alternative configuration - but more expensive ;(
    @rhuck60
    the problem is i will built the light with a 2x18650 tube, so there is no chance for parallel connection.
    @TigerhawkT3
    why schould i fry them ? i think the boards have an internal resistance, so this configuration should work like a voltage divisor ?

    But i would say the best would be the solution from TorchBoy...
    the first LED (for voltage dropping), is connectet in a row with the board, so both devices get the same current (max 1A). Should be save...
    By the way i think this configuration would even be more effektive then one board for one led...

    if this works nearly a perfekt solution

  16. #16
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    Default Re: 2 LED Driver Borars in a Row ?

    Let me say again.
    3x li-ion 18650 in serial => (1.2A AMC7135 to cree) + (1.2A AMC7135 to cree) + (1.2A multi-level AMC7135 to cree)
    The multi-level AMC7135 board control the current to all cree, work quite well with 3x P4 cree.

  17. #17

    Popcorn Re: 2 LED Driver Borars in a Row ?

    Quote Originally Posted by TigerhawkT3 View Post
    Since no one has yet said so in this thread, I'd like the opportunity to say that

    NO

    you cannot put two driver boards in series and feed them double their speced voltage. You'll fry them.
    "ahem"
    .____________________
    |.............................. |
    |.............................. + R1
    |.............................. |
    = battery (8.4 volts) ,o.|
    ||||........................... + R2
    | ............................o.|
    |___________________.| R1 = R2

    this basic electronic circuit is known as the "resistive voltage divider".

    the voltage each resistor sees is exactly half the battery voltage if the 2 resistances are equal.
    The 2 driver boards with their leds will be very close to the same load (resistance) and so each will see 1/2 the battery voltage. Trust me!
    Last edited by rhuck60; 01-02-2008 at 02:55 PM.

  18. #18

    Default Re: 2 LED Driver Borars in a Row ?

    Quote Originally Posted by J.D. View Post
    @rhuck60
    the problem is i will built the light with a 2x18650 tube, so there is no chance for parallel connection.

    No problem. just go with your original idea, making sure the driver boards dont need an Led connected to survive.


    But i would say the best would be the solution from TorchBoy...
    the first LED (for voltage dropping), is connectet in a row with the board, so both devices get the same current (max 1A). Should be save...
    By the way i think this configuration would even be more effektive then one board for one led...

    pretty sure this wont work right, let me think why and get back to you.

    if this works nearly a perfekt solution
    when you get the boards first hook one up and test it, then unhook the led and turn it on again. Then turn it off, hookup the led and test it again. If it survived running unloaded you have crossed your first obstacle.

    Im not sure if one of those boards will run 2 Cree XR-E's or just one.
    Last edited by rhuck60; 01-02-2008 at 02:59 PM.

  19. #19
    Flashaholic* TorchBoy's Avatar
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    Default Just one LED driver board

    This is more the sort of discussion I like to see - much more interesting than a monologue from me.

    My suggestion was only to have one board running one LED (but with another LED in series with the whole thing, either on the positive or negative side). Because of the high forward voltage of white LEDs the board won't cope with driving two LEDs unless they're red LEDs, with their lower operating voltage (1.7-2.0V).

    Or you could just put multiple signal diodes (not LEDs) @ ~0.6V each onto the positive side of the control electronics - I think they already come with one for polarity protection and a bit of voltage protection. BTW, the 5 mode board from DX is sold out.

    A single mode 3xAMC7135 board doesn't burn out if an LED is not attached. If the multimode boards just add switching I can't see them burning out either.

    As I've mentioned, using an LED in series with the board (which itself is driving another LED) will save a little bit of voltage over using two boards in series. It might be handy when the battery voltage lowers as it goes flat and you want to use high mode (1A) since the forward voltage of the LEDs will be higher. The minimum battery voltage would be (by spec) 2 x 3.7V + 0.12V = 7.52V, rather than 2 x 3.7V + 2 x 0.12V = 7.64V. Of course, you can get much lower Vf LEDs than that, so it might not be a problem for the particular LED you use.
    No, a torch does not always mean flames.
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  20. #20
    Flashaholic* 2xTrinity's Avatar
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    Default Re: 2 LED Driver Borars in a Row ?

    this basic electronic circuit is known as the "resistive voltage divider".

    the voltage each resistor sees is exactly half the battery voltage if the 2 resistances are equal.
    The 2 driver boards with their leds will be very close to the same load (resistance) and so each will see 1/2 the battery voltage. Trust me!

    This works if the drivers behave as resistive. In this case, you're using linear drivers which essentially drop off any excess voltage using resistors until the proper output voltage is reached. IF you were to try this with buck or boost drivers however, which operate using inductors and operate on a non-continuous duty cycle, it won't behave as a simple voltage divider anymore.

  21. #21
    Flashaholic* TorchBoy's Avatar
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    Default 2 LED driver boards not so good

    Quote Originally Posted by 2xTrinity View Post
    This works if the drivers behave as resistive. In this case, you're using linear drivers which essentially drop off any excess voltage using resistors until the proper output voltage is reached.
    So both would try to drop all the volts, and may not come to rest at a happy mid point. And before they sorted themselves out to come to a balance, one or the other might burn out.
    No, a torch does not always mean flames.
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  22. #22

    Default Re: 2 LED Driver Borars in a Row ?

    So LDOs work fine in series, but some drivers (such as buck or boost ones, or ones containing an inductor) may ? Is that the nutshell?

  23. #23
    Flashaholic J.D.'s Avatar
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    Default Re: 2 LED Driver Boards in a Row ?

    Interesting discussion ...
    Can´t wait to receive the boards to play with them.

    btw kaidomain has the multimode 3xAMC7135 in stock ...
    Last edited by J.D.; 01-04-2008 at 07:58 AM.

  24. #24

    Default Re: 2 LED driver boards not so good

    Quote:
    Originally Posted by 2xTrinity
    This works if the drivers behave as resistive. In this case, you're using linear drivers which essentially drop off any excess voltage using resistors until the proper output voltage is reached.


    Quote Originally Posted by TorchBoy View Post
    So both would try to drop all the volts, and may not come to rest at a happy mid point. And before they sorted themselves out to come to a balance, one or the other might burn out.
    One thing to remember is that you dont have to reach the "happy midpoint".
    The driver boards operate at up to 6 volts each.

    So long as one board drops a minimum of 2.4 volts you are within the limits of the other driver.

    I think this will allow for difference in PWM switching, if used. (meaning that they will probably not be switched on or off at the same time)

    Please remember that voltage rise unloaded or fall under load is not instantaneous.

    To make sure it would work, I would hookup the 2 drivers in series, one with an led connected and one without. Thats the worst case situation.

    Then using a DMM measure across the plus and minus terminals of the 2 driver boards. As long as one is less than 6v and the other is more than 2.4v you should be OK.

  25. #25

    Default Re: 2 LED driver boards not so good

    double post. lots of database errors last 24 hours. Barely able to get on or reply for 24 hours now.
    Last edited by rhuck60; 01-03-2008 at 12:45 PM.

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