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Old Feb 28, 2013, 05:37 PM
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How can I lower voltage from 4cell to 3cell


I'm building a quad copter and will be running it on 4cell lipo (because I already have them). And plan to add 12vdc led strips on all four arms. Is there an easy way to build a micro step down xformer thats small and light. I'm sure the draw will be very low like 500 mah. I could test them w my multimeter I guess
Last edited by superinstaller; Feb 28, 2013 at 05:48 PM.
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Old Feb 28, 2013, 05:58 PM
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http://www.fairchildsemi.com/pf/LM/LM7812.html
Old Feb 28, 2013, 06:19 PM
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Will this work? These guys have good prices! How do I wire these ??


http://www.westfloridacomponents.com/T278PD/view.html
Old Feb 28, 2013, 06:28 PM
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Page 22 of the datasheet has the typical schematic.
http://www.fairchildsemi.com/ds/LM/LM7812.pdf
Old Feb 28, 2013, 07:09 PM
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I think you are overlooking the easiest way... Power it off of the balance leads at the third cell connection...
Old Feb 28, 2013, 07:41 PM
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I thought of that I want less work and more flying/crashing
Old Mar 01, 2013, 07:54 AM
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Quote:
I think you are overlooking the easiest way... Power it off of the balance leads at the third cell connection...
Be aware that this will cause an imbalance in the pack cells.
Old Mar 01, 2013, 10:25 AM
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http://dx.com/p/m1201-dc-3-40v-to-1-...or-blue-177634

Cheap, better in many ways. Still reg you linked too and few other parts would get job done would be about same money (well maybe not)
Old Mar 01, 2013, 10:25 AM
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Agreed, but the imbalance would be minor. I have a plane with a lot of LEDs on it and it still only draws about 1 amp. Small in comparison to the power needed to fly a plane, let alone a quad. Balance charging will correct the imbalance easily.
Old Mar 03, 2013, 08:59 AM
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You cannot determine whether the imbalance would be minor or not as the imbalance would depend on the current draw of the LEDs and the time they were on.
Old Mar 03, 2013, 03:08 PM
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If you want to power anything off only a few cells, you'll want a lipo alarm that monitors every cell. If your lipo alarm (or esc capability) only monitors the total voltage of the pack, you'll risk destroying some of the cells in your battery.
Old Mar 04, 2013, 06:13 PM
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My goal is to make a regulator (or buy) that is permanent and needs no extra pluging and unplugging, I'm always up for a new trick and cheap is that much better!
Old Mar 04, 2013, 06:45 PM
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Nice find, I will try find one in country. Tks for the help.
Old Mar 04, 2013, 07:18 PM
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For reducing the current for an LED when the source voltage is higher than the operating voltage of the LED, just use a resistor.
According to the calculator http://led.linear1.org/1led.wiz
You would want 8.2ohm at just over 2W. Radio Shack has a 3W 10ohm resistor (a $1.89) part# 55050389. Should work fine, actual resistance is not all that critical, I would tend to err on the high side.
Pete


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