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
Link restored. Make sure you read the comments about inductive loads exceeding the voltage rating of the LTC4415.
Dean
Hi everyone...
On page 2 of this thread Dean Franks posted a schematic or PCB layout but the link is dead....
does anyone have a copy of this file?
Im trying to make the LTC 4415 work with 2 turnigy lownoise 3A SBECs.
thanks
jeff
Hi Robert, I fly fixed wing, heli's(all sizes), and now a quad too.
On the quad, no big issue, since I get power from 4 BEC's.
On the other stuff..........
Peak servo current probably will exceed the capability of your average BEC/UBEC.
And that can give the hardware a "brown-out", exactly when you don't want it.
A (small) NiCad, or NiMh pack acts like a "super capacitor", with one HUGE difference.
It's internal impedance.
Just google the specs on "super caps"
Scary.
Even a lowly 6800 uF capacitor has a better low impedance, but for a short while, than "super caps"
As I said, cheap, easy insurance.
That's not the application I'm working on. If a speed controller goes, I can still fly... well... controlled descent. I need 6V up to 5A for servo outputs. I don't think a 600mAh pack will cut it. Not for long anyway. And without some form of intelligence, you wouldn't know to land before I've depleted the battery.
Also, none of this protects you from overvoltage.
If you're flying a quad, why use a BEC at all? 4 cell 600mAh pack should be good for almost 3 hours.
Remember, the original idea of the BEC circuitry in a speed control is to eliminate the independent battery for the radio (Battery Eliminator Circuit). To use a BEC, but then put the receiver battery back in because the BEC isn't realiable seems a bit... questionable to me?
Yes, even a common 4 cell 600mAh pack on the rx/apm should keep the "brain" alive.
If a speed controller decides to depart, you have zero options anyway.
I've been keeping this one quiet, until I'm happy, now I am.
On my Drastik 160, I have two switches, one switches a NiCad pack straight to the Spektrum RX,
The second switches a 2S LiPo through a UBEC straight to the same RX. (5V)
No diodes.
Even a depleted NiCad pack, with 4 good cells, draws very little current from the UBEC.
I just make sure the NiCad pack is semi charged, at least, before flying.
I see no point, in pulling the pond out, from underneath the duck.
So, anybody have any good ideas for the 6V supply side of this? Are there any chips we could use for 5A @ 6V?
lol! Indeed :)
LOL, that's the discussion that got this all started in the first place. :)
As for of quality of equipment, if only there was some good way to measure this. Some believe buying higher priced American ESC's it the best. Unfortunately, many of them have a terrible failure rate.
@Johann: Its for my octo, which has a stand alone BEC. Obviously if the esc BEC on a quad failed. It would still fall out the sky... Although im not sure when a bec fails on a esc, does the esc fail as well or is it the other way around? Do they both fail together. I would imagine the BEC circuit can potentially fail without the ESC failing but not the other way around.
What do you think?
G:)
That sounds like a plan :)
-
1
-
2
-
3
-
4
-
5
of 11 Next