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  1. #1
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    Drive 2 XP-G's in parallel w/ bFlex/BuckPuck?

    Instead of driving 2 XP-G's in series with an 11.1v pack...can I drive them in parallel with a 7.4v pack w/ the same results?

    I'd like to use the same pack on my double barrel w/ a bFlex or BuckPuck as I have for Quazzle's boards.

    Would this double the amperage requirement? (I don't know these things)

  2. #2
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    Quote Originally Posted by chelboed
    Instead of driving 2 XP-G's in series with an 11.1v pack...can I drive them in parallel with a 7.4v pack w/ the same results?

    I'd like to use the same pack on my double barrel w/ a bFlex or BuckPuck as I have for Quazzle's boards.

    Would this double the amperage requirement? (I don't know these things)
    If you drive them in parallel, the current is divided between them. However, there might be other problems you wish to look at before taking this route. runaway etc.

  3. #3
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    Hi there CB, the current will be split. 500mA going to each led. You would need 2 bflex or buckpuck drivers. This would drive both led's at 1 amp, 1 driver per led. This configuration will also need a larger battery. I find it easier to think of the battery in watt/hours. An 18650 cell has about 9 watt/hours. So, 3 cells 3s would be 27 watt/hour battery. 6 cells 3s2p would be 54 watt/hours. 2 XPG leds at 1 amp will draw about 6.5 watts, current controller will draw a couple watts. Total 8.5 watts. Using your 27 watt/hour battery, 27 watt/hours/8.5 watts=3.2 hours run time. Twice the time on 6 cells. But, back to now, I would prolly run the XPG's in series. James

  4. #4
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    That's what I was thinking...but hoping wouldn't be true.

    Mmmmkay...thanks.

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    brain explosion please ignore!!
    Last edited by doogs; 07-12-2010 at 05:44 AM.

  6. #6
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    Yah...I'll prob. have to go that route. I really don't want something I need to sink, but ya gotta do what ya gotta do, right?

  7. #7
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    Quote Originally Posted by doogs
    a boost driver like a maflex would allow you to run the leds in parallel from your 7.4v pack
    This is not correct!! The Vf of your XP-Gs in parallel will only be ~3.2V. To use a boost driver like a MaxFlex the battery voltage must be lower than the Vf of the LEDs. You will burn out your LEDs if you try what doogs is suggesting.

    Even running 2 XP-Gs in series (~6.4 Vf) off a 7.4V battery with a MaxFlex is likely to cause smoke as the battery will actually be ~8.3V fresh off the charger. The maxflex will effectively run in "direct drive" while the battery voltage is equal to or higher than the LEDs Vf.

    You could run your 2 XP-Gs in series with a Bflex and your 7.4V battery. You will fall out of regulation part way through the runtime. Only side affect to that is a gradual dimming of the light as the batteries run down. Some people actually prefer that as a way to gauge how much runtime they have left.

  8. #8
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    Hmmm...will the same thing work with a BuckPuck?

  9. #9
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    Quote Originally Posted by Vancbiker
    This is not correct!! The Vf of your XP-Gs in parallel will only be ~3.2V. To use a boost driver like a MaxFlex the battery voltage must be lower than the Vf of the LEDs. You will burn out your LEDs if you try what doogs is suggesting.

    Even running 2 XP-Gs in series (~6.4 Vf) off a 7.4V battery with a MaxFlex is likely to cause smoke as the battery will actually be ~8.3V fresh off the charger. The maxflex will effectively run in "direct drive" while the battery voltage is equal to or higher than the LEDs Vf.

    You could run your 2 XP-Gs in series with a Bflex and your 7.4V battery. You will fall out of regulation part way through the runtime. Only side affect to that is a gradual dimming of the light as the batteries run down. Some people actually prefer that as a way to gauge how much runtime they have left.
    yeah you are right brain explosion on my behalf typed without thinking!!

  10. #10
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    Quote Originally Posted by chelboed
    Hmmm...will the same thing work with a BuckPuck?
    I'm planning on setting up 2 XP-G's in series with a buckpuck ( recom rcd-24-1A from cutter ) and a magicshine battery (2s2p 18650 ) so I'm very interested in this thread.

  11. #11
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    Quote Originally Posted by chelboed
    Hmmm...will the same thing work with a BuckPuck?
    Yes.

    Be sure to use protected cells or a protected pack though. The buckpuck does not have any ability to monitor battery voltage and it is easy to overdischarge. The ability to set voltage monitoring and temp monitoring is the real strength of the flex series drivers IMO.

  12. #12
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    Cool.

    Yah, I build my battery packs with a protection circuit. It'll probably be that LiMnNi 26650 4000mAh pack that I'm digging so much with my L33.2

  13. #13
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    Quote Originally Posted by Vancbiker
    You could run your 2 XP-Gs in series with a Bflex and your 7.4V battery. You will fall out of regulation part way through the runtime. Only side affect to that is a gradual dimming of the light as the batteries run down. Some people actually prefer that as a way to gauge how much runtime they have left.
    At what point does the Bflex drop out of regulation? Would this setup work with 6V, or is the drop-out point higher than that? I'm asking because I have some 6V lithium primary packs I use.

    I agree, dropping out of regulation's not a bad thing when the battery's getting low. It's better than a blackout in the middle of nowhere.

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    6v primary lithiums START at 6V, they will drop to 5V pretty quickly, especially under load. Primary lithiums are pretty hopeless at higher currents (like 1A or more).

    With primary lithiums and 2 series LEDs you would need a maxflex to boost, but again, primary lithiums are hopeless in high current applications.

    cheers,
    george.

  15. #15
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    Quote Originally Posted by georges80
    6v primary lithiums START at 6V, they will drop to 5V pretty quickly, especially under load. Primary lithiums are pretty hopeless at higher currents (like 1A or more).

    With primary lithiums and 2 series LEDs you would need a maxflex to boost, but again, primary lithiums are hopeless in high current applications.

    cheers,
    george.
    Thanks George. Are you saying that it'll drop out of regulation at 5V?

    I use the Lithium AAX4s as backup to my main rechargeable batteries, and on multi-day races when we can't recharge.
    They do OK for my 3x R2 iBlaast II that Eric set up for 6-7V.
    Last edited by Ofroad'bent; 07-12-2010 at 09:52 AM.

  16. #16
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    Quote Originally Posted by Ofroad'bent
    At what point does the Bflex drop out of regulation? Would this setup work with 6V, or is the drop-out point higher than that? I'm asking because I have some 6V lithium primary packs I use.

    I agree, dropping out of regulation's not a bad thing when the battery's getting low. It's better than a blackout in the middle of nowhere.
    A 2S XP-G light with a bFlex and 6V battery of any chemistry will never be in regulation. A rough idea is add 1V to the Vf of the LED string. This would give the minimum battery voltage required to be regulated.

    You might find that a 2S XP-G light would run on the 6V battery pack with no driver. The Vf of the LED string is ~6.4V the battery is 6V. If the battery is incapable of delivering more than 1.5A you will not blow a well heatsinked light. A good example is to look at a 3S AAA led flashlight. The Vf of the led is 3.5V but the battery is 4.5V. It doesn't burn out because the battery does not have enough current. Connect that same led to a 3S AA battery and it will leak smoke. You would need a driver or a resistor to control the current.

  17. #17
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    I drove 2x XP-G's through a 1Amp BuckPuck with a 7.4v 2000mAh LiPo for 2hrs and 7 minutes today. It began to dim toward the end of the 2hrs...but worked really well considering that my 11.1v 2000mAh battery cut off at 2hrs 45sec.

  18. #18
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    Quote Originally Posted by chelboed
    I drove 2x XP-G's through a 1Amp BuckPuck with a 7.4v 2000mAh LiPo for 2hrs and 7 minutes today. It began to dim toward the end of the 2hrs...but worked really well considering that my 11.1v 2000mAh battery cut off at 2hrs 45sec.
    Did you measure the output current? With a buck driver, it could have been dimming for quite a while without you 'seeing' the dimming. The eye responds logarithmically to light intensity, so output current can easily drop from 1000mA to 700mA (for example) and you would barely notice the difference over time.

    With a 3 li-ion pack (assuming protected cells), it would stay in regulation a lot longer - basically to the point that the protection in the cells kick in a leave you in instant darkness. With 2 li-ion the protection wouldn't kick in till the batteries were maybe at 6V (or lower) and you would be dimmed quite a bit at that point - i.e. it would noticeably dim versus just instant darkness.

    You basically need to understand your battery pack, whether the cells are protected, how buck drivers work and to measure actual output current to really know what is going on.

    cheers,
    george.

  19. #19
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    I understand my battery pack. I built it. I soldered in the protection circuit.

    I should have said "The light didn't dim significantly until toward the end of 2hrs." I built one of these using an 11.1v pack and I agree that it didn't dim visibly at all throughout the battery life. There was just a question as to whether or not you could run 2 XP-G's this way...and someone already stated previously in the thread that it'd work barring dimming toward the end. I just wanted to prove it to myself.

  20. #20
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    Quote Originally Posted by chelboed
    I understand my battery pack. I built it. I soldered in the protection circuit.

    I should have said "The light didn't dim significantly until toward the end of 2hrs." I built one of these using an 11.1v pack and I agree that it didn't dim visibly at all throughout the battery life. There was just a question as to whether or not you could run 2 XP-G's this way...and someone already stated previously in the thread that it'd work barring dimming toward the end. I just wanted to prove it to myself.
    No worries - I just wanted clarification that it would NOT be in regulation with 2 li-ion cells and 2 LEDs for the entire runtime - just so folk that search the forum don't assume it would be. Most buck drivers require around 1V of headroom to regulate (especially at higher output currents like 1A).

    cheers,
    george.

  21. #21
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    Aaaahhhh...I think the best option for this is probably a boost circuit or the 11.1v pack. I really, really like the 11.1v pack b/c it's so tidy, small, and lightweight. Works with the Buckpuck very well.

  22. #22
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    Quote Originally Posted by chelboed
    I drove 2x XP-G's through a 1Amp BuckPuck with a 7.4v 2000mAh LiPo for 2hrs and 7 minutes today. It began to dim toward the end of the 2hrs...but worked really well considering that my 11.1v 2000mAh battery cut off at 2hrs 45sec.
    Did you try running it with a bFlex at this voltage?

  23. #23
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    I thought I'd re-awaken this thread with a question- Would it be more sensible to just drive 2 XP-Gs with a dimmable Buckpuck and a potentiometer, rather than playing with all the difficult combinations?

  24. #24
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    Quote Originally Posted by Ofroad'bent
    I thought I'd re-awaken this thread with a question- Would it be more sensible to just drive 2 XP-Gs with a dimmable Buckpuck and a potentiometer, rather than playing with all the difficult combinations?
    2XPG in series, ~6.5V Vf. Add 2V to get the buckpuck into regulation, then you need a batterysorce of atleast 8.5V. 3x18650 lithium cells will do for you. I have a rule of thumb when using buckpuck: for n XPGs you need n+1 Li-ion cells. Its nice to work with the buckpuck because it has no exposed electrical surfaces to short. But I don't see why bFlex should cause any trouble.. ?

    Edit: also remember that with a bFlex, you get a regulator needs +1.1V (at 1000mA) more voltage on the input than the output, where as the buckpuck needs +2V..
    The bFlex has a max inputvoltage of 25V, where as buckpuck has 32V (or 36?) cant remember. Not important.
    If you choose the bFlex, you get the 5 bicycle mode button, but with buckpuck you would need more electronics to do the same. But yes you could use just a pot. there are waterproof pots out there..
    Last edited by bwack; 09-16-2010 at 11:10 AM.

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    ---
    Last edited by Ofroad'bent; 09-17-2010 at 05:15 AM. Reason: Duplicate

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