Wondering if i might ask those of you with far superior electrical knowledge than me (thats most of you lol) a question...

I'm building a hex for aerial photography and have been planning a dual battery in parallel for redundancy.

We're using the APM2.6 and would like to use it's PM so i can monitor the voltage through the GCS.

Trouble is, that PM is limited to 70 amps (from memory) and the ESCs will draw up to 120.

So i've thought that instead of making a 3 plug parallel harness i could make up a 4 plug and run 2 systems. One side for the motors (direct wired to the parallel harness) and the other side for accessories like gimbal et al (wired from the APM PM which runs back to the parallel harness).

My question is in a couple parts:

-am i introducing a short in the system?

-will i get accurate voltage readings?

- is there some quantum effect that i'm missing (lol- but i do think of electricity like water and am aware that it not always the case))

- am i just crazy?

- your thoughts?

Sorry for the noob question; i just don't want to wire this up and watch my first effort at this smoke up a couple grand and weeks of my spare time.

I've attached my planning schematic (i stand ready to be flamed for my horrid lack of electrical drawing skills!). You can see the wiring harness i plan above the batteries. The APM PM is on the Right (top) system, and the motors/ESC are on the left (bottom). The two power distribution boards before the gimbal et al and the ESCs are those cheap ask ones from HK which are supposedly good for 160 amps each.

Thanks for any and all advice,

Windjimes

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I might get 13s on without lengthening the arms, but deeper 12s is easy. 14s would be a pita, but do-able although i may be pushing the frame a little far from it's intended design.

Looks like i can run the 10s with a single battery and basically bare frame. Didn't think of dropping the 2nd battery yesterday. Thats good enough for now to get her flying. I've got to setup the EvvGC, fatsharks, head track, vid tx/rx, fpv... the list goes on and on. At least this way i can get out of the sim and start practicing a bit with the hex, with the risk of breaking all the extras.

How accurate are the ecalc flight times? Doing A/P would i expect to get closer to flight, mixed or hover times? I guess it depends a lot on how windy and turbulent it is?

Thanks for picking up my errors earlier... you saved me making a quick pile of CF and wood!

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Yes, I run the schottky diodes on my Skywalker which provides redundant power for my APM, servos, and FPV gear.
In my last plane I used a separate FPV battery, and on a subsequent flight I went to swap out the little battery, but got distracted and mistakenly put the depleted battery back on. I was surprised to discover that I lost all video halfway through the next flight. One of the weaknesses of the APM is that it only monitors 1 battery voltage where nearly every other OSD will monitor two packs. As an airline pilot I am very well trained to recognize that I make mistakes all the time, and I will never stop making them. Designing checklists, procedures, and systems designed to handle my screw ups is the only way to assure safety.
I like my Schottky design because it takes out a lot of human error.

Perfect thank you... exactly what i needed. Apart from parallel batteries and still using the APM PM (until the attopilot module arrives) i have the same system now.

I have a question(s) though and, although i think you have answered it in your other posts, i would appreciate the confirmation;

The ESCs should only have a single signal wire run to each of them from the appropriate APM outputs? The  red/black power wires are neither needed nor advised?

Same thing with the receiver in so far as i run a single set of red/black from the 5v rail on the APM  to power it and then only single signal wires for each channel?

If so thanks again for taking the time to post this as i had already wired RX-APM with 3 wires on each channel and was about to start on the ESCs... plus those servo wire and clips are so bloody small...

I wasn't aware of that about APM, or to be more correct i wasn't aware that other systems allowed for multiple pack monitoring. Something to look at in future, especially if we get into fixed wing services and i can run shottkys. 

Seems we share a profession... my other acft is a 747. If this tech will put us out of work one day i figure its well time i got prepared ;)

Thanks again for your help

Yes that is correct,only single wires like on the scheme of my post. That is because the ground is shared in common on all APM rails and you should always avoid ground loops.

Schottky diodes has a dropout voltage of (in the best case) of 0,3V

With 120 Amps the power loss is P=V*I = 0,3*120=36W...

A lot of power will be disspated in heat and the diode could burn very soon. We developed an ideal diode controller with a very low voltage dropout. It remains cold even if you have a 100A flow and all the energy is provided to the UAV circuit without losses.

iskess said:

This wont work. You can't expect redundancy by just using parallel wiring. If one battery malfunctions the other will try to charge it, possibly too fast which could cause a fire. The batteries need check valves so one can't charge the other and they stay independent. Schottky diodes are such a check valve.

Yeah. the use of diodes for this is arcane; even multiplexing 5V power inputs as in the PixHawk. Note that if the diodes are properly rated, they won't "burn". Simply put, simple use of a few of today's high power, low cost MOSFETs that were not available five years ago will do the trick! Look at how today's ESCs are now using only a few MOSFETs instead of a bank of 12 or more. However, I have run two 4S 80C(120C burst) batteries in parallel and NEVER had an issue.  However, these were hard-case (racing car certified), so they had extra protection from crash damage.

...old posts live on and still have relevance!


Marco Riccardo Napoleone said:

Schottky diodes has a dropout voltage of (in the best case) of 0,3V

  1. With 120 Amps the power loss is P=V*I = 0,3*120=36W...

A lot of power will be disspated in heat and the diode could burn very soon. We developed an ideal diode controller with a very low voltage dropout. It remains cold even if you have a 100A flow and all the energy is provided to the UAV circuit without losses.

iskess said:

This wont work. You can't expect redundancy by just using parallel wiring. If one battery malfunctions the other will try to charge it, possibly too fast which could cause a fire. The batteries need check valves so one can't charge the other and they stay independent. Schottky diodes are such a check valve.
A real galvanic separation and a dry parallel are very different.. You didnt have any problems for years but you wasted a lot of energy in reverse current, that's true..

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