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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
Comments
where you use this setup ? plane or rotorcraft ?
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
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)?
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...
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
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.
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)?
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
Or you could just use one of these:
http://www.linear.com/product/LTC4415
Or the 4416.
Second thoughts : this crowbar circuit can only work if you have a 1Volt differential between the source and the trigger voltage of the diode. As we know APM accepts a voltage range between 4.8 and 5.25, we just have a 0.45V difference margin to trigger the circuit which is unsufficient.
I'm afraid this would not be the best solution, except maybe by using semiconductor voltage sensing circuits ? like here : http://www.onsemi.com/PowerSolutions/product.do?id=MC3423
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