OpenXsensor and receiver battery backup

[jhsa]

As you guys know I have no idea about programming whatsoever.. But i have been researching for similar projects that could be adapted to do this. I did find some but then I thought, Why couldn't the oXs do this? So I decided to share the idea here. This is probably very useful for people that fly gliders and IC powered models.

The idea is to carry a smaller battery in the aircraft and switch to it if the voltage of the first battery pack falls under a certain threshold.

-When the voltage stays under that voltage for a couple of seconds, the arduino would switch to backup power.

-In case of a big voltage drop on the main circuit (for example a short circuit), the arduino should switch to the backup power immediately.

-The arduino would switch ON the backup battery before disconnecting the main battery to avoid resetting. (maybe the arduino could be powered from both batteries using 2 diodes, if one dies it will be always powered and decide what to do). For example, in the unlikely event it was already in backup power as a result of lower voltage, and the backup system suffers a catastrophic failure, the arduino would still be powered by the nearly empty main battery and switch the receiver to it again. We would need a lot of bad luck for this to happen, but Murphy likes to surprise us

- Power to the receiver should switch to the backup battery if the arduino fails

2 Mosfets could be used connected to two digital pins of the Arduino. The arduino is probably already monitoring the voltage so no additional analog input is required.
HHmmmm, Actually, an extra ADC would be needed for the backup battery and the arduino would switch to send this value instead of the main batt voltage when this battery is being used.
The arduino would also send an alarm to the tx using one of the unused telemetry fields so the pilot would know that the model is running on backup battery power..
I think as far as hardware is concerned, this should be quite simple.

As I said above I think this could be a great safety feature for gliders and Nitro/Gas planes.

João

[Kilrah]

Sounds overly complicated and an added source of failure when a common dual battery supply even as simple as 2 diodes will do the job...

[jhsa]

This is exactly to avoid failure.. If 2 diodes were enough, the power boxes you can buy would use them. The thing is, diodes have voltage drop and also normal ones can't handle a few amps..
Also, as far as I know the 2 diodes will only help if one of the batteries fail completely?? You wouldn't probably even know that the backup battery was being used?

This adds the same level of failure as for example the taranis radio controlling the power to the module via a mosfet and software..

João

[Kilrah]

This is exactly to avoid failure.. If 2 diodes were enough, the power boxes you can buy would use them.

They pretty much all do actually. Sometimes with added voltage regulators to allow for more battery types but that's it. Current handling is way more than enough with the correct parts.

This adds the same level of failure as for example the taranis radio controlling the power to the module via a mosfet and software..

No, because the module is either on or off and that's controlled by a clear menu option. You're describing something that needs bullet-proof logic and timing to do the right thing at the right moment based on potentially unreliable measurements.

You wouldn't probably even know that the backup battery was being used?

Useless IMO, you'll see it when you recharge your 2 batteries. But most existing powerboxes give you readings for voltage of each battery and/or notify you of any unusual drops while in use anyway.

[jhsa]

Well, I don't agree. I think a circuit like this would give more safety than just 2 diodes. If I thought it was like that I wouldn't have bothered to research about this. As I said I do believe this add as much failure points as the RF module ON OFF circuit on the taranis. Both use mosfets (or fets) and both use software. The idea is just monitor one battery and switch to the other in case of some problem. As I understand with the diodes the circuit is powered by both batts at all times.. that is not what I am trying to do, nor think I that is a decent option.
I just shared my idea and I start to regret it. I respect your opinion but i have a different one. I was expecting some comment from the people that develop the oXs. I will continue my research and do some cut and paste and try to make something out of it. I already have some ideas.
Next time I have an idea I just don't bother sharing..

João