Flight pack battery redundancy question - RCCanada - Canada Radio Controlled Hobby Forum
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Old 03-15-2007, 06:33 PM   #1
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Flight pack battery redundancy question

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I would like to put a backup/standby battery pack in a large model where I have a larger number of servos and intend to do some longer duration flights.

Some years ago, I recall someone simply putting two battery packs in parallel, but with diodes on the positive lead of each. That should mean that, if one pack went lower in voltage than the other, the higher output one would continue to supply power to the electronics without feeding back into the weaker battery. Does this sound right? Does anyone out there use this apparently very simple technique?
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Old 03-15-2007, 06:53 PM   #2
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My set-up

That is one way of doing it,but what happens is you have a switch failure?
You could use two packs,one plugged in the regular slot on the Rx and the other one in any unused servo slot on you Rx.that way you have the capacity of the two batteries and the safety of a switch failure.I do not see a problem with using a diode in between the two packs,it is probably a good idea.

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Old 03-15-2007, 07:45 PM   #3
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flight pack backup

I tried the diode idea & went into fail safe on take off . Was told it was that you can only use the diode idea if using 6 volts -5cells rather than the normal 4,8 vlts -4 cells . So now i have 2 batts; & 2 switches using the batts plugged in as "PEP" said . Have read the 2 batts this way is as good as the diodes & the extra switch is a bonus .
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Old 03-16-2007, 06:52 AM   #4
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Another variant

OK - if one uses 2 packs, one of 4 cells with a diode and one of 5 cells with no diode, then the 5 cell pack would be powering everything unless/until it drained down below (4.8 + the voltage drop across the diode), which would hopefully still leave enough voltage to power the system for awhile. Right?

As I do not use failsafe, and the receiver should still operate down to something like (3.8 volts, as I recall?), this looks fairly good to me.

With very large aircraft that have many servos and/or high current drains, do folks usually make up a power bus arrangement so that certain servos are powered by one battery pack, the rest by another and then the signal lines carry through to the receiver(s)?

I very much appreciate, and enjoy, any and all comments in response to my questions.

As for switches - depending upon the model, I often do not use a switch, just plug the battery directly into the receiver (preferrably) or into an extension that goes to the receiver. While to some, this may not make sense, and possibly be a bit worrisome due to wearing of plug contacts over time, I do this on my SPAD things and these have spent many, many hours in the air with the connectors flailing around in the slipstream, with never a failure or working loose.
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Old 03-16-2007, 09:57 AM   #5
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another option

As for switches with lots of servos I would think it may be nice to be able to turn them off when you are not flying by moving a switch or inserting a pin. Futaba heavy duty switches are reportedly the best mechanical switches on the market.

Also use heavy duty servo extensions
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Old 03-16-2007, 01:34 PM   #6
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battery redundancy

If you put the diodes on the 4 cell batt; it will be a waste of time , that is what happened to me . The diodes take a good amount out of the voltage , think is is .6 of a volt ? My batts were fully charged , but as i was taking off it went into fail safe -because the batts were reading low , . When I checked with mick Reeves [ a world class flyer] in UK who had sent me the schematic with the diodes in he said it has to be a 6 vlt /5 cell system because the diodes take the batts down in voltage . So only use the diodes on 6vlts . Using switches is surely a much prefered way of putting the radio on & off . I have been using 2 batts & 2 switches for a few years now at 4.8 /4 cells without diodes and no probs .
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Old 03-16-2007, 07:37 PM   #7
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Here's another reason why I really like Multiplex IPD receivers. The 9 and 12 channel IPD receivers have two battery ports specifically for 5 cell batteries. The receiver has an internal voltage regulator on each port and manages the batteries itself. I just plug in two 5 cell batteries with their own switches (and their own charge leads) and I'm all set.

You can still use a single 4 cell pack, but it must be plugged into one of the servo ports.

The synth IPD receivers can be used with any transmitter in PPM (FM) mode.

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Old 03-17-2007, 11:35 AM   #8
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Heres what I do in my giant scale planes. I like the KISS principle. Your mileage may very...

I run two receivers, each on two separate circuits. Each has its own battery [6V NiMH] and switch.

I plug one elevator and one aileron [opposite, that being left A and right E] into one receiver, the other two into the other receiver. My rudder usually has two servos, so one into each receiver. Throttle and choke [gas engine] are then also split up between the two receivers.

If one receiver, battery or switch should fail, [not a hold condition from interference] the other side still working, is enough to land the plane. While I have never had to do this myself, I have witnessed this a # of times, and it did save the plane.$$$$

Hope that helps.

Mike Clemmens
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Old 03-17-2007, 12:21 PM   #9
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I have basically the same set up as Mike 2 rec. 2 batteries and 2 switches coreless servos. I have had a in flight battery failure in my 33% cap232 and was able to land with 1 aileron 1 elevator and throtle.

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Old 03-20-2007, 01:37 AM   #10
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I third what Mike said. I have my big Yak split in half, each half with it's own system. Rudder on 1 half and throttle on the other.

I've had to land with 1 elevator once when the little wire pulled off the matchbox (my fault I didn't check it when setting it up) was no big deal so I sort of have a feal of what it would be like to land with only one half working.
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