Dual redundant BEC + overvoltage protection (crowbar circuit) to power the flight controller?

or ?

Hi, when i fly multirotors one of my main worries is to avoid it from crashing. Mechanically I've practically solved it because I usually fly an octocopter (motor, prop and ESC redundancy). My main concern right now is how to power the flight controller safely.

Initially I've connect all my 8 linear becs (in parallel) to my flight controller because I thought that if one fails, the rest would supply the required power. Later on I found out that a linear regulator may fail and may supply voltages higher than 5v and that would burn the flight controller.

A fuse is the easiest approach to solve this but I've read that sometimes it doesn't work well (fast enough). So i found the Crowbar Circuit.

So, i would use 2 linear BECs for redundancy and the crowbar circuit after each of the becs so in case it fails it will not burn the flight controller:

Another option:

I had the idea to use a switching BEC but i don't know if it's the best alternative. I've read that you cannot put 2 switching BECs in parallel because the voltage is generated in waves that may interference each other. So to solve this, one switching bec would be in use and if it fails, the backup switching BEC would take place.

The diagram for this is shown below:

If the SBEC number 1 fails, the Schottky diode would alternate to the SBEC number 2. I think that using 2 diodes would be better for the redundancy (i don't know if it's ok to do that). Could I use a relay instead of this diode?

What do you guys think? Will it work? Any idea is very welcome! ;D

Does anybody have the part list to do a crowbar circuit for the APM? I think it should supply 5v and 500mA, is that right?

Best regards

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Comments

Bernardo M. A. September 23, 2013 at 2:44pm

iskess, Rambo and Nick, thanks for the feedback

eduardo, i don't know if it was for me, but i'll use it with a multirotor
eduardo September 21, 2013 at 1:35pm

where you use this setup ? plane or rotorcraft ?
Nick Arsov September 21, 2013 at 9:15am

Hi Bernardo,

Have a look at these ICs:

http://www.ti.com/lit/ds/symlink/lm5050-1-q1.pdf

http://www.ti.com/lit/ds/symlink/tps2419.pdf

http://www.ti.com/lit/ds/symlink/tps2411.pdf

http://www.ti.com/lit/ds/symlink/tps22981.pdf

http://www.ti.com/lit/ds/symlink/tps2115a-q1.pdf

http://www.ti.com/lit/ds/symlink/tps2113a.pdf

http://www.ti.com/lit/ds/symlink/tps2112a.pdf

http://www.ti.com/lit/ds/symlink/tps2111a.pdf

http://www.ti.com/lit/ds/symlink/tps2110a.pdf

and more ICs here:

http://www.ti.com/lsds/ti/power-management/power-multiplexer-mux-pr...

You need to choose the right one for your needs with respect to needed current and voltage.

Best regards

Nick

http://www.ti.com/lit/ds/symlink/lm5050-1-q1.pdf
John Rambo September 21, 2013 at 4:43am

wouldn't it make more sense to replace Schottky diodes with Mosfets for boosting efficiency some 10 times? (voltage drop of few hundred millivolts vs some 30mV)?
iskess September 20, 2013 at 7:46pm

Take a look at my redundant power system plan using Schottky diodes in the form of a product called Batshare.

http://www.rcgroups.com/forums/showpost.php?p=25660816&postcoun...

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Bernardo M. A. September 20, 2013 at 4:58pm

Phil P, the problem is that I'm planning to use the APM with 6s batteries and the 3DR power module support just up to 4s =/

Do you know if anybody has already used 2 APMs with a circuit to change to the other one in case of a failure? That will be great but may be too complex
Phil P September 20, 2013 at 4:53pm

If you use the 3DR power module you should be just fine. It's heart is a very good quality TI part. Much more reliable than any no-name BEC.
The weakness would be in the APM and subsequent systems. If you have a short circuit down stream of the APM there is nothing that will help the situation. That's when you move to two separate APMs and a changeover circuit, and the weight penalty for doing so. So you have two choices. Add redundant systems or make the single system you have as reliable as possible.
Bernardo M. A. September 20, 2013 at 3:36pm

hughes, thanks for the detailed information about the circuit! ;) since this circuit is not ok for APM i'll try something else

R_Lefebvre, thanks for the info, i'd take a look. I found it on ebay. If you have the circuit for powering APM with this LTC4415 would be possible to share with us?

Nick, could you tell me the name of some of this ICs so I can search it on ebay or other online website? I found the following IC, is it ok for powering the APM?

L3100B - OVERVOLTAGE AND OVERCURRENT PROTECTION FOR TELECOM LINE

http://pdf.datasheetcatalog.com/datasheet/stmicroelectronics/3025.pdf

Have you guys already seen a switching bec fail (midflight)?
Nick Arsov September 20, 2013 at 9:15am

I would bet on Robert's idea! You may also have a look at TI power mux ICs.

As the current drawn from APM is less than 500mA, you may use a simpler circuit for OV protection such as those used in USB devices. It is cheaper and could be implemented just with 1 device.

Note, most of the 5V power muxes use integrated OV protection.

Best regards

Nick
Rob_Lefebvre September 20, 2013 at 4:41am

Or you could just use one of these:

http://www.linear.com/product/LTC4415

Or the 4416.

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