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Thread: Electrical figuring required

  1. #1
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    Electrical figuring required

    Greetings boffins, I want to cobble a campsite 'streetlight' by putting an LED flood lamp atop a tall pole and powering it with 18 volt (6A/Hr or 9A/Hr) Makita drill batteries.
    the lamp is as follows:

    LED Qty 4 x 3W
    Lumen Effective 489lm, Raw 660lm
    Draw
    @13.8V 0.59A
    @28V 0.27A


    Given that I'd like the lamp to be powered for 5 or 6 hours and should probably not completely flatten the batteries, how many and which size batteries would I need.
    Thanks
    Don.

  2. #2
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    Those numbers don't add up.
    12W (4x3W LEDs) @ 13.8V is 860mA.
    The numbers indicate more like 8W, and 8W @ 18V is ~444mA.

    6 hours of that is 2.6Ah, so either of your batteries will do it lying down in the sewer after a hard night on the sauce.

  3. #3
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    It doesn't add up. But if it were really 12 watts, rule of thumb is 12w @ 12V = 1A therefore @18V (which would be closer to 18.5V using a drill battery) = 0.67 amps. Allow for a bit of wear and tear and I reckon if you allowed 8 hrs for 6 ah and 12 hrs for 9 ah you'd be playing it pretty safe.

  4. #4
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    Homestar is offline Super Moderator & CA manager Gold Subscriber
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    Probably 3 watt LEDís that are current limited so they last rather than being driven at full load.

    So as mentioned, either battery will do it easily. If you wanted multiple nights from one charge, go the 9Ah unit - would last almost 3 nights doing 5 to 6 hours each night.


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  6. #6
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    Hi Don,
    I am not sure if you are aware but the BMS for the Makita batteries is in the tools / charger, so I believe it is possible to drain those batteries to destruction.

    Cheers Glen
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    When I grew up there were 9 planets.

  7. #7
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    I was under the impression that the bms is in the batteries, but, I think Glen is correct

    Do Makita Power Tool batteries have built in over discharge? | Second Life Storage & Solar

    One of the replies in this thread stated from there experience that Makita have the bums in the tool

    Maybe find an old tool and see if you can remove the bms or look at investing in another battery

    Gav
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  8. #8
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    Quote Originally Posted by Gav 110 View Post
    I was under the impression that the bms is in the batteries, but, I think Glen is correct
    When I was playing around with a similar idea, I found that some brands have the BMS in the battery and some in the tool.
    From memory you can get the Makita BMS unit as a spare from fleabay etc.
    I gave up as it got too hard for my idea which was a bit more complex.

    Cheers Glen
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    Sold 99 D2 TD5
    When I grew up there were 9 planets.

  9. #9
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    Thanks for the heads up Glen. I didn't know of that issue. I'll investigate further before taking the plunge.
    Don.

    And after another look at it, yes you can get the charging/BMS module from the web but then it all becomes messy and complex

    BL1830 Li-Ion Battery BMS PCB Charging Protection Board for Makita 18V PowerC2W5 4894822113439 | eBay

    Don.

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