Driver help for a Cree XP-G2 Triple

mbanzi

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Nov 2, 2015
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I have a Cree XP-G2 S3 Triple MCPCB left over from a dynamo project that I'm planning to use for a battery powered light.


  • What's the best approach to take with a triple? Do I keep them in parallel and run them at 3V or serial at 9V?
  • Any recommendations for driver boards (3 mode is ideal) & battery configuration (1-3S)?

Thanks!
 

Steve K

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Peoria, IL
In theory, running the LEDs in series is the best way to ensure that they share current equally.

In practice, if the LEDs were sold as part of the same group, they probably are very similar in terms of forward voltage and internal resistance, so they should perform well enough if you wire them in parallel.

My only guidance regarding drivers is that switching power supplies operate at the highest efficiency when the voltage of the power source and the voltage of the load are close to each other. This would suggest using a 3.7V battery to drive a 3V LED array (using a buck converter), or perhaps using two lithium batteries in series to drive three 3V LEDs in series (using a boost converter).
There may be higher priorities that optimal efficiency, though.
 

mbanzi

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Nov 2, 2015
Messages
37
Thanks Steve. BTW, I'm going to start up the MPPT dynamo driver project again soon - expect many questions then!

In theory, running the LEDs in series is the best way to ensure that they share current equally.

In practice, if the LEDs were sold as part of the same group, they probably are very similar in terms of forward voltage and internal resistance, so they should perform well enough if you wire them in parallel.

My only guidance regarding drivers is that switching power supplies operate at the highest efficiency when the voltage of the power source and the voltage of the load are close to each other. This would suggest using a 3.7V battery to drive a 3V LED array (using a buck converter), or perhaps using two lithium batteries in series to drive three 3V LEDs in series (using a boost converter).
There may be higher priorities that optimal efficiency, though.
 

Steve K

Flashlight Enthusiast
Joined
Jun 10, 2002
Messages
2,786
Location
Peoria, IL
Thanks Steve. BTW, I'm going to start up the MPPT dynamo driver project again soon - expect many questions then!

cool! I keep meaning to find time to do some basic tinkering with a buck converter and seeing if my theories about what should work actually do. Nothing fancy.... just adjusting the duty cycle and seeing what happens to the power delivered to the load. The next step might be to become acquainted with the Atmel uC and implement the MPPT with it.

On the various bike forums, I do see people who want to be able to charge batteries while touring, so it would be nice to have a mode for the MPPT where it pulls 6 watts from the dynamo, delivering 3W to the headlight and 3W to the battery being charged. This gets tricky, I suspect, because I don't know how much power the average bike headlight will draw. I think some of them require AC power, so it might not just be possible to convert the dynamo power to a DC voltage using the MPPT.
Anyway.... while it's interesting to contemplate this stuff, I need to get the basics done first! :)

Hope to see some results on your MPPT soon!
 

Lexel

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Sep 15, 2016
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Location
Germany
If you want to charge battery and drive light you will need a MPPT running at 4.2V max and CC higher than the LED draws
and simply connect it parallel to the Battery

so transform AC to DC, get a capacitor and then Step down converter at 4.2V and the LED + charge current
 
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