Battery mod Devo7e

clearprop88 wrote: I just wired up a 2s 1200mah lipo for my Devo 8.
.....

Not sure about the Devo8.. but if it can work down to 3.3V so that it can be powered by 1S, then using 2S is a waste of battery juice...

One can always split a 2S and connect them in parallel to give a 1S with doubled capacity. So a 2S 1200mAH becomes 1S 2400mAH. The running time increases from 6 to 12 hours...

and the transmitter is way lighter than using NiMH

Hi cmpang
As 1x2400 = 2x1200, I don't think that 1S will give 2 more playing time.
TX does not need current only (A), it need power (A x V).
When you reduce voltage, you increase the current.
It will probably give a little bit more playing time cause there is no power loose in the 2 diodes in series added by clearprop88, but that's all (but there will be more power loose in the regulator cause the current will be higher) .

domcars0 wrote: Hi cmpang
As 1x2400 = 2x1200, I don't think that 1S will give 2 more playing time.
TX does not need current only (A), it need power (A x V).
When you reduce voltage, you increase the current.
It will probably give a little bit more playing time cause there is no power loose in the 2 diodes in series added by clearprop88, but that's all (but there will be more power loose in the regulator cause the current will be higher) .

while the current is the same, (about 220mA for 150mW RF power output) any voltage higher than 3.3V is just dissipated as heat (mainly in the inernal voltage regulator) inside the transmitter... you lose the voltage and hence the power which is V x A

you can verify it very easily.. measure both currents while the battery is fresh and while the battery is nearly flat... and you'll get the same reading..

for information, I tested my 7e with a 500mAH battery from my V929 and it gives a bit more than 2 hours running time.. so a 2400mAH projected to about 10 hours..

Both of you are right, depending on whether the TX has a switchmode PSU or a linear voltage regulator to take the incoming battery votage down to 3.3V.

Based on cmpang's measurements showing a constant current at different battery voltages, the TX uses a cheap old linear regulator. All the voltage higher than 3.3V x the current drawn goes up in the air as heat. The inline diodes suggested will drop the Battery voltage to a save voltage that can be handled by the regulator and secondly they will help in dissipating the extra heat.

cmpang wrote: while the current is the same, (about 220mA for 150mW RF power output) any voltage higher than 3.3V is just dissipated as heat (mainly in the inernal voltage regulator) inside the transmitter...

OK ... that means that the WK regulator is a very poor regulator

domcars0 wrote:
..... that means that the WK regulator is a very poor regulator

not necessary so... while reliability being the most important concern in our radio, embedding a switch regulator inside poses a risk of interference to the control circuit... and that is the reason why I won't use 2S and step the voltage down with a UBEC..

using NiMH is no big issue.. just weights a bit more and takes a longer time to recharge... not convenient if some buddy calls for a adhoc flight session...

...but having a second pack in the tx case also resolves this.

www.rctw.net/viewthread.php?tid=241130&page=97#pid2046918

just read that the Devo 12s is using 1s battery and a switching regulator to step down to 3V...

may be that is why PB said somewhere that the 12s is rather noisy.....

Thanks cmpang for your explanations.
So now it's very clear for me why I will keep my NiMH

domcars0 wrote: Thanks cmpang for your explanations.
So now it's very clear for me why I will keep my NiMH

Exactly excellent splendid!

And an extension cord to my belt with 12s 4000 in parallel for an 7 day all-nighter .

ok the thread is old, but isn´t it possible to use a 1s lipo plus a step up module (as used in power banks to output 5V).
Is there a problem with the ripple?

specs of a step up module:
Input voltage: 2.5V-6V
Output voltage: 5V
Output Current: 1000mA (Max)
Conversion efficiency: 92%
Switching frequency: 1MHz
Output ripple: 20mV (max)
Load Regulation: ± 0.5%
Voltage Regulation: ± 2.5%