Question: DIY BEC and Lipo's

[ek123]

Hello,

I just bought several low dropout regulators (MIC29500-5) to build several BEC's for some of my planes. Originally I had intended to purchase some 2S lipo's and then regulate the voltage using the LDO regulator. Now I'm thinking about the following--instead of using a separate 2S lipo what if I tap into 2 of the 3 cells in my 3S pack through the balance/charging connector on the battery? This will eliminate the need for the additional 2S lipo. The problem I see is that, since I am using the system on powered sailplanes, I could be drawing down the 2S lipo's 'much more' than the 3rd cell. In principle, this could lead to a problem where the ESC cuts off the 3 Lipos at the set cutoff but the 2S cell voltage is lower than what would be the case if all 3 cells are drawn down equally.

In practice I wonder if this would really be a problem.

Comments/criticisms?

Thanks,

Eusebio

[vintage1]

Don't go there. Straight into battery imbalance.

Either do teh job from teh full pack volathge using a linear and some extra heastink, or ecxteranl power device(s) or simply buy a smartBEC from dimension engineering.

[Chippie]

I agree with V1....the problem is that you will draw more from the 2 cells, thus creating the imbalance...better to avoid it altogether and use the 3 cells.

[ek123]

Like the title says!

Thanks for the comments,

Eusebio