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BEC or Voltage Booster, noob question...

#1
I'm building a (hopefully) light weight wingeron glider. its 90cm wingspan.
with all electronics and 4 AAAA nimh batteries its a little nose heavy and 130g total weight.
with only 2 AAAA batteries the CG balances perfectly at around 115g .
The AAAA batteries are 400mah each for only 7g weight each. not bad at all.

I would like to make that 2 battery arrangement work if possible,
I've searched the forum and interwebs and gots hints of an answer but nothing concrete.

The RX wants 5-6v
I tried a cheapo voltage booster from amazon, only 1g weight, which was fine for the RX alone, but was only rated at 480ma,
the servos just clicked and did nothing, and the voltage to the RX fluctuated wildly when trying to use the servos.

the 4 battery AAAA setup works fine to power RX and servos... but its the heaviest part of the build at about ~33g for the batteries plus holder

So the questions...
1) is there a good light, voltage booster out there, maybe capable of 2 amps, commonly used, that would work for this? and where an I buy it from please?
2) or could there be a problem with max amperage deliverable from 2 NiMH batteries? or is it the 480ma booster causing the problem?
could they power both RX and 2 micro (5v) servos at the same time ok ?
3) 1S lipo + booster, if so, what booster please ?
4) or should I buy, 2s lipo, bec voltage reducer
option 1 would be much cheaper if it could work... 3 and 4 will work, but be more pricey setup. but if so, any recommendations on electronics appreciated.


any thoughts or ideas appreciated, thanks
 

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Piotrsko

Elite member
#2
Lipo.
A single cell perhaps 850mah capacity will weigh the same as your 2cell nimh pack and last far longer but has better voltage at 3.8 nominal versus 2.5 ish.
For servos, a rule of thumb is 3/4 amp each so you're looking at 2amps minimum. A nimh step up pushing that much power gives you perhaps 2 minutes useful flight.

You need either a system that tolerates 1 cell lipo, one that works on 8.4 (high voltage), or a bec.
 
#3
Thanks Piotr, the 1s lipo doesn’t provide enough voltage for the RX So I’d need a booster or 2S with bec. As you suggest.

I’m surprised the nimh will only last a couple of minutes in a glider. The 4 battery nimh lasts an hour easily with charge to spare. I guess the booster takes a big extra tax on a 2 battery nimh setup?

I guess the total Mah is not the whole picture when it comes to charge capacity. even though the nimh would total more Mah the lipo would last longer ?
 

Piotrsko

Elite member
#4
Thanks Piotr, the 1s lipo doesn’t provide enough voltage for the RX So I’d need a booster or 2S with bec. As you suggest.

I’m surprised the nimh will only last a couple of minutes in a glider. The 4 battery nimh lasts an hour easily with charge to spare. I guess the booster takes a big extra tax on a 2 battery nimh setup?

I guess the total Mah is not the whole picture when it comes to charge capacity. even though the nimh would total more Mah the lipo would last longer ?
You need to think in terms of watts (electrical work) more voltage [4 cell] means less current draw, voltage step device up needs 2-3 times more current to get same watts, and nimh/nicad chemistry current tends to just drop like a rock below a voltage threshold. Enough to give you a headache.
 
#5
thanks much for the explanation :) appreciated
ahh, yep, my old school friend ivy watts. I * V= Watts
makes sense, thanks, I'll do some more battery research.
 
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