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  1. #26
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    Quote Originally Posted by yetibetty View Post
    It might be an idea to explain the three main types of driver (buck, boost & linear) as it's a constantly asked noooob question. Oh and the bit of extra battery voltage over LED forward voltage required for buck and a bit less battery voltage than LED forward voltage required for boost etc.

    Don't forget to explain what forward voltage is too

    Good write up BTW keep it up.
    Thanks! I knew almost none of that stuff before last night and your suggestion is new to me. Any threads that already explain it?
    No, YOU don't understand. You're making an ass of yourself for all of eternity.

  2. #27
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    That's the problem, there are bits and pieces on the subject all over the forum. I'll have a search and see what I can find.

  3. #28
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    easiest rule of thumb for number of cells is:

    buck driver - no. of LEDs + 1

    boost driver - no. of LEDs - 1

    pretty simple

  4. #29
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    Oh, quick research shows that you'd use a buck driver if your battery pack's voltage is higher than rated and boost driver is opposite, correct?

    So, in my example, a 4-cell pack in series would yield 16.8V at max charge and the driver is rated for 6-18V. What type of driver would be appropriate?
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  5. #30
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    it's the relationship between the voltage (Vf) of the LED string and the voltage (Vin) of the battery. For a buck driver Vin>Vf and a boost driver Vin
    So the battery voltage does not dictate the driver, the no. of LEDs (and how they're wired) and the battery voltage together do.

    Using your example, a 4 cell pack would happily drive a 3 series LED string using a buck driver or a 5+ series LED string using a boost driver. The voltage range of the driver merely states the voltage range within which it can work, not whether it's buck or boost or how many LEDs a given battery within that range it can drive.

    Just use the rule of thumb I posted above, honest, it's really that simple. If you want to run a 2 series LED light, then you either need a 3 series cell battery and a buck driver (most likely) or a 1 series cell battery and a boost driver. If you use a buck driver it must be able to accept a Vin of up to 12.6V. If a boost driver then it will have to go down to 3V.

  6. #31
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    Uploaded with Imgupr

    Thank you for all your knowledge and patience! Yetibetty gave me access to a pic and it explains they why behind what you are saying. It seems to me that a goal of a good lighting system is to minimize heat. Using a several cell series to create high voltage in tandem with a buck driver seems like the best scenario, right?

    It makes sense that you can't always get this scenario with a multiple light set up, so, a boost driver is required.
    Last edited by wmac; 12-30-2012 at 03:19 PM.
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  7. #32
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    There is a bit of a hiccup in that diagram now that XMLs are coming in at about 3 volts VF
    making is easily possible to drive 4 XMLs from a 4 cell battery pack and a Buck driver .

  8. #33
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    Quote Originally Posted by troutie-mtb View Post
    There is a bit of a hiccup in that diagram now that XMLs are coming in at about 3 volts VF
    making is easily possible to drive 4 XMLs from a 4 cell battery pack and a Buck driver .
    There is more than a hiccup I wasn't expecting it to appear on here. All numbers are very approx and as usual I'm out of date

  9. #34
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    Pic removed.
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  10. #35
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    You can put it back I don't mind at all. I would have spent a little more time on it if I knew it was for world wide viewing, that's all. If it's not back soon I'll sulk

  11. #36
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    If you want to pull some info on buck/boost linear drivers etc (direct cut/paste is fine) feel free to use my faq as a resource:

    Frequently Asked Questions

    cheers,
    george.

  12. #37
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    It's back Yeti. Thanks George!
    No, YOU don't understand. You're making an ass of yourself for all of eternity.

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