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Old Mar 22, 2003, 06:47 PM
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Vermont
Joined Mar 2002
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Any dc-dc converters for 1 lipoly to 6v?

I see lots of 5v voltage boosters around, but I'd like to get 6v from a 800mah lipoly. Is it easy? Hard? Not worth it?

Thanks.
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Old Mar 22, 2003, 10:00 PM
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Wheat Ridge,co
Joined Nov 2002
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There is no demand for stepup converters. It is cheaper and more efficient to use a 2 cell pack with a 400 mah. The the stepup converter only has an 80 to 90 % efficiency and it will weight much more than an extra battery pack.
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Old Mar 22, 2003, 11:08 PM
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Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
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The more volts you boost, the lower the efficiency. So, going from about 4v to 6v is less efficient than from 4v to 5v. Also, you have to consider the current draw. Most of the planes people are flying with voltage boosters tend to have low amp draw pager motors, which often like higher volts. Hence the need for a voltage booster. What really matters is the total weight of the battery/motor and any booster.

Gordon
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Old Mar 23, 2003, 03:08 AM
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MSC Rödinghausen, Germany
Joined Feb 2001
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Hi all,

I have built a booster for 5.2V at a time where the 145mAh LiPolys were not available, so I needed to make at least 5V from one 650mAh LiPoly cell for an N-20 motor. Besides that I have made a booster to 9V from two Tadiran cells to power a Tiny. At this time I would rather use three 145mAh cells in series for the same purpose.

Gordon is right, the pagers need the boosters, but using one they are happy with one 145mAh cell. An alternative could be using two 40mAh LiPoly cells in series, but their current capability is limited. Basically a booster allows to use less cells if lighter cells are not available for your special purpose.

Another reason for the 5V is that some of the very small DC booster chips have a fixed output voltage of 5V, since these chips are designed to supply logic circuits in small portable devices (cellphones, pdas and so on).

Regards, Jochen
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Old Mar 23, 2003, 03:59 AM
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MSC Rödinghausen, Germany
Joined Feb 2001
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fdisk,

I forgot to answer your initial question. Using for instance the LT1930 or LT1930A from Linear Technologies building a 6V booster is no bigger problem than for 5V. Just use a different voltage divider (two resistors) for feedback. If you need more current then the LT1308 is an option.

Another reason for using 5V is that you can directly power your rx and actuator drivers from it. The widely used PIC chips are limited to max. 5.5V supply voltage.

Regards, Jochen
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Old Mar 23, 2003, 08:15 AM
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Vermont
Joined Mar 2002
2,706 Posts
Thanks for all the facts and opinions. I'll fess up now to the reason for the question.

I have a Hobbico Sky Sailer (which I have yet to fly) and it comes with a 6v (5 cell) 2/3 AAA 300 mah nimh pack. I also own two 800mah lipoly's. I hate peaking nimh/nicad cells before flying so I was thinking of using the lipolys, but I was worried that 7.2+V might kill the plane and it is definately heavier than the little brick pack that came with it. The BEC won't even run the motor on one lipoly so I know I needed more volts. I'm pretty broke so I was just seeing how feasable it would be to boost one cell. It sounds easier to get a pair of 540's and use a resistor to go to 6v.
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