High power voltage divider

[Les Jones]

Kiss,
The TL494 would solve the problem so that the output was always a fixed fraction of the input. I suspect that the OP is using one of the cheap boards from China that use the LM2596 (Just a guess.) so he would have to build the regulator.
Spec,
I did think about your series parallel battery pack idea but I assumed that the OP had chosen the series arrangement as he required the higher voltage for some other purpose. If he did require the higher voltage (So long as it was not for something requiring a large current such as the main motors) then he could use your battery arrangement with a step up regulator.

Les.

 

[spec]

Kiss,
The TL494 would solve the problem so that the output was always a fixed fraction of the input. I suspect that the OP is using one of the cheap boards from China that use the LM2596 (Just a guess.) so he would have to build the regulator.
Spec,
I did think about your series parallel battery pack idea but I assumed that the OP had chosen the series arrangement as he required the higher voltage for some other purpose. If he did require the higher voltage (So long as it was not for something requiring a large current such as the main motors) then he could use your battery arrangement with a step up regulator.

Les.

Hi Les,

Yes, I am not too clear about the requirements but, hopefully, Avalan will clarify the position for us.

Good idea about the step-up regulator if a higher voltage is required for another purpose.

spec

 

[Les Jones]

Here is a way to implement my suggestion from posts #9 and #12

**broken link removed**
When the regulator voltage input is above the "battery low" level Q1 will be conducting which will cause Q2 to conduct. The regulator output voltage will be set by the ratio of R6 in series with R7 and R8 in parallel. When the regulator input voltage is below the "battery low" level Q1 and Q2 no longer conduct so now R8 is no longer in parallel with R7. This will cause the output voltage to fall. The values of R6, R7, and R8 will have to be calculated to gine the required output voltages.

Les.

 

[Avalan]

spec: When powering the brushless motors (rated from 6 to 12 cell) from a 8 cell battery pack it can achieve higher RPMs and generate more thust allowing it to carry heavier payload. So the idea is not really to increase the endurance, in which case running two packs in parallel would for sure make more sense. Its one battery pack with 8 identical cells connected in series.

For more information:
Not the battery I am using but very similar:
http://www.hobbyking.com/hobbyking/...ght_8S_12000mAh_2C_Multi_Rotor_Lipo_Pack.html

The motors:
http://www.rctigermotor.com/html/2014/Efficiency-Type_0314/198.html

@KISS: Thanks for the reference to tl494, I will study the datasheet tonight. Regarding your previous question. The autopilot needs 6 cell (max), the motors I want to power from 8 cells. But since I am not using 2 battery packs and only 1x 8 cell pack I need a way to provide the autopilot with between a 3 and 6 cell voltage levels.

les: Thanks, I now have a better understanding, this also seems like it could work. At the moment I am still looking at a more generic solution. Say I wanted to quickly change the failsafe threshold for some reason (doing longer flights and need the trigger earlier to have enough capacity to fly home, etc.). This is still a valid option though.

I have attached a basic picture to explain the situation. It only shows the power connection, between the autopilot and motor there is obviously control lines.

 

[Les Jones]

The preset resistor sets the voltage at the 8 cell battery at which the output voltage of the step down switching regulator reduces its output voltage. You could add a switch to select the output from a few potentiometers set to different trigger levels.

Les

 

[Avalan]

The preset resistor sets the voltage at the 8 cell battery at which the output voltage of the step down switching regulator reduces its output voltage. You could add a switch to select the output from a few potentiometers set to different trigger levels.

Les

Hi Les, sorry I typed the reply before seeing your circuit. Thanks, yes, this could for sure work and isn't too complicated. I will give it a try.

 

[spec]

spec: When powering the brushless motors (rated from 6 to 12 cell) from a 8 cell battery pack it can achieve higher RPMs and generate more thust allowing it to carry heavier payload. So the idea is not really to increase the endurance, in which case running two packs in parallel would for sure make more sense. Its one battery pack with 8 identical cells connected in series.

For more information:
Not the battery I am using but very similar:
http://www.hobbyking.com/hobbyking/...ght_8S_12000mAh_2C_Multi_Rotor_Lipo_Pack.html

The motors:
http://www.rctigermotor.com/html/2014/Efficiency-Type_0314/198.html

@KISS: Thanks for the reference to tl494, I will study the datasheet tonight. Regarding your previous question. The autopilot needs 6 cell (max), the motors I want to power from 8 cells. But since I am not using 2 battery packs and only 1x 8 cell pack I need a way to provide the autopilot with between a 3 and 6 cell voltage levels.

les: Thanks, I now have a better understanding, this also seems like it could work. At the moment I am still looking at a more generic solution. Say I wanted to quickly change the failsafe threshold for some reason (doing longer flights and need the trigger earlier to have enough capacity to fly home, etc.). This is still a valid option though.

I have attached a basic picture to explain the situation. It only shows the power connection, between the autopilot and motor there is obviously control lines.
View attachment 97380

Hi Avalan,

Many thanks for all that information. Not only is that a great help, but it is interesting too.

spec