So after much reading and research into the whole "backup" BEC saga. I think I've found a solution!
My first idea was just to run a 5.5v backup lipo in parallel with the 5v UBEC output.
This idea has been vitoed by most. Too many unknowns apparently.
The other was to parallel all the BECs up, but this would cause harmonics due to all the square wave interaction.
So I figured we cant mix power supplies. Other than using a microproccessor controlled mosfet to switch
power supplies when and if the bec dies.
We use a relay :) Bear with me.
The main power supply powers the relay. With the relay closed (NO) power is routed via the bec to the apm.
If the bec fails, the power to the relay fails and is switched to the auxillary power supply (battery or another bec)
This completely seperates the two power sources.
Will the relay be able to switch fast enough to the auxillary power source without the APM losing power?
If not, im sure a power capacitor will keep the APM alive long enough for the bi-pass surgery to take effect?
Above is a recording of the ciruit just in case my explaining skills are dodgy :)
You need to be a member of diydrones to add comments!
Comments
Gareth,
If you look at the power distribution board, and the way it is connected, it is very easy to see where to mount 4 diodes, to feed the single + wire going to the APM.
If you want to use diodes.
Jani, the standard Quad distribution board only takes power from one of the BEC's.
I still think it won't be a problem just to connect all the + lines together, there are enough holes on the board to do that.
Geez guys, other than the power board, what I say, I've done, it works.
The built in voltage regulator on te eAPM1.4 cannot supply enough power to supply the APM without overheating. I don't really know why it was chosen.
if people are afraid about 0.4 volt drop off, you can always add small resistor on those 7805 regulators to make them output a bit higher voltage. And if doing BEC or uBEC from scratch you can always make them to output like 5.5 - 5.6 volts so then voltage that is lost on shottky diodes does not matter at all. As 5.5 - 0.4 = 5.1V
APM electronics works best when voltages are +5V like 5.0 - 5.3V. And btw APM1.0 there is separate input for external battery if someone want to make sure that APM always get's fresh and clean power.. Just hook up one 2S lipo on it's private power input and you are done.
Quad/Hexa setups that has multiple ESC/BECs providing power to main power rails do not have any problems. It is just one BEC that provides main prover for whole system, if it fails nextmost powerfull will continue. BECs on all ESCs are linear anyways.
Robert: Yes the switchover will be automatic. You could use diodes on the input if you are paranoid, the voltage drop there will not make any difference to the outputs and that will absolutely prevent a shorted (or reversed) cell from taking down the redundant 78SR and the 5V output.
I will breadboard the two 78SRs without the input diodes today and make sure they are stable with one input shorted, etc and report back here.
Will you share the circuit diagram when u have it?
Next thing I'm doing is to OR the outputs from all 4 BEC's on my quad,
Now THAT will give me some redundancy, and current oomph!
Battery goes through a switch to spare RX port, if none, use a Y-lead.
BEC goes to throttle port.
Previously I didn't even use diodes, never had any funnies.
Used on Spektrum and FRsky equipment.
I don't like to speculate and theorize, I do :-)
AWESOME! Thank you Gustav for the real world advice :)
Yes, in the BEC + line.
So you put the diode in the BEC + line not the Battery + line?
-
4
-
5
-
6
-
7
-
8
of 10 Next