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  1. #1
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    What LED driver do I use with a Cree MC-E?

    I want to power one cree MC-E LED with a 12 volt 5 amp/hour SLA battery. I want to get a driver but I'm having input/output voltage problems. With a buckpuck the Vin has to be at least two volts higher than the LED (14) and with a boostpuck the Vin has to be two volts lower (10). I thought powering a 12 volt led with a twelve volt battery would be easy but boy was I wrong.

    My question is, is there an LED driver out there which inputs and outputs 12 volts with the output being constant current.

    Thank you

    -Jacob

  2. #2
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    get the mce in a 2s2p configuration and then you can use a buck driver

  3. #3
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    How many volts would it require if it was in that configuration?

  4. #4
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    Quote Originally Posted by Noblenutria
    How many volts would it require if it was in that configuration?
    6 to 7 volts plus what ever the driver needs, normally 1 to 2 v. Problem with it is the current output is halved, ie if the driver is 1000mA as pictured by leopold, each led only sees 500mA

    Leopold, will that driver stay in regulation very long with the forward voltage of an MCE and a 12v battery?

  6. #6
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    Quote Originally Posted by emu26
    get the mce in a 2s2p configuration and then you can use a buck driver
    I can't put it in the 2s2p configuration because the star I got is already wired to run in series. I have a boostpuck so I need to lower the voltage somehow. A guy from ledsupply said to use an 8 or 9 ohm 5 watt resister but that would waste electricity, wouldn't it. Is there a simple component that would convert 12 volts to 9 volts?

  7. #7
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    Quote Originally Posted by Leopold Porkstacker
    The guy from ledsupply said buckpucks and boostpucks only work with a voltage drop s there are no drivers which convert 12 v from a battery to 12 volts constant currents. I can't use a buckpuck because it would only work if I had a 14 volt battery.

  8. #8
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    The forward voltage at 700 ma for the MCE 4s is almost 14V. So you would need a higher voltage battery for that. Also, you can't use the buckpuck shown because it is 1000 ma. You would fry the MC-E.

  9. #9
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    Are you making a bike light? If so, a SLA battery isn't a great choice because they are really heavy compared to other choices.

    As you've already discovered, it's also not a good choice from a driver point of view. You would need a combination buck-boost driver and since they're more complicated, they are not nearly as common and will be expensive. You'll be better off picking a different battery.

  10. #10
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    Quote Originally Posted by Prophet Julio
    Also, you can't use the buckpuck shown because it is 1000 ma. You would fry the MC-E.
    Maybe not. My dual MC-E light runs each LED at 1000mA (HipFlex at 2A setting) now for the last few months. They are very well heatsinked though. Not really sure it is worth the slight gain in light versus the battery drain and extra heat though. More of an experiment really.

  11. #11
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    Quote Originally Posted by MtbMacgyver
    Are you making a bike light? If so, a SLA battery isn't a great choice because they are really heavy compared to other choices.

    As you've already discovered, it's also not a good choice from a driver point of view. You would need a combination buck-boost driver and since they're more complicated, they are not nearly as common and will be expensive. You'll be better off picking a different battery.
    I bought a boostpuck driver before I realized I was going to have problems. Could I still use it if bought a buckpuck. I would connect the boostpuck to the 12 volt battery, and that would up the voltage to 14 volts, then input to the buckpuck, then the buckpuck would step the power back down to 12 volts. Would that work?

  12. #12
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    Quote Originally Posted by emu26
    6 to 7 volts plus what ever the driver needs, normally 1 to 2 v. Problem with it is the current output is halved, ie if the driver is 1000mA as pictured by leopold, each led only sees 500mA

    Leopold, will that driver stay in regulation very long with the forward voltage of an MCE and a 12v battery?
    I use 14.8V Li-Ion battery packs, so no idea on the 12V packs. I guess I missed the part about using a 12V pack (boost versus buck, in the case here).
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  13. #13
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    Quote Originally Posted by Noblenutria
    I bought a boostpuck driver before I realized I was going to have problems. Could I still use it if bought a buckpuck. I would connect the boostpuck to the 12 volt battery, and that would up the voltage to 14 volts, then input to the buckpuck, then the buckpuck would step the power back down to 12 volts. Would that work?
    You just need to bite the bullet and just get the right battery/driver combo. Get some 18650 Lith Ion cells and chargers from deal extreme.

    Don't mess around with screwy driver stuff like you suggest, I don't see how it would ever work.

  14. #14
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    Quote Originally Posted by Noblenutria
    I bought a boostpuck driver before I realized I was going to have problems. Could I still use it if bought a buckpuck. I would connect the boostpuck to the 12 volt battery, and that would up the voltage to 14 volts, then input to the buckpuck, then the buckpuck would step the power back down to 12 volts. Would that work?
    No, it won't work because the buckpuck is a current driver as opposed to a voltage driver. It would technically work if the buckpuck were a voltage regulated driver, but it would be horribly inefficient.

    If you've already bought a boostpuck, then buy a battery that'll work with that driver.

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