If you don’t like to power down your Heli at every battery change, and losing your GPS fix... there is a solution.

Just install a parallel second battery connecter (can be a much smaller one), prepare an old battery with the matching connector and a Diode in the + wire as a backup battery.

(To charge the backup battery you have connect the charger behind the diode)


Before changing the main battery connect the backup to the 2.connecter, change the battery, disconnect the backup and go flying again without loss of GPS fix and so forth.


By the way I had a very successful first flight with my T-Rex450 Pro and APM2

in stabilize mode. Very stable Tail and Hover, unfortunately the weather turned bad I had to stop.

Will keep you posted.

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  • @R Lefebvre
    With my TX, VRX, FPV Goggles, laptop, Lipos, GoPro and video camera, I really don't want any more batteries to charge ;)
  • IMO, you should all be running the APM on a seperate power supply from the main motor supply in any case, so this whole discussion is sort of moot.  Doing this easily solves the problem of the OP, and brings a lot more benefits.

    Even on my little 450 heli, I simply use a 2S 800 pack that weighs almost nothing, and can power the APM and servos for the duration of several flight packs.

  • Simplicity is bliss :)

  • @Carl
    Or just a single super cap on a spare input on the APM. No switches, diodes or anything.
  • The diodes on the flight pack will have to handle all that current. 

  • @Muhammad
    A super cap on a spare APM input channel would indeed be far more elegant.
    As this blog has the potential to be dangerous (unlimited current pouring into a Lipo even for a short time) and/or ruin Lipos should the post remain without a warning?
    elegant.as is parked
  • If I'm thinking of this correctly, the diode will only stop the main battery from trying to balance with the smaller one, but won't stop the smaller one from trying to balance the main, Correct?

    A small supercap somewhere after the BEC would seem like a much more elegant solution. 

  • Alternatively, use a small 4-cell NiMh pack in parralel with the 5v power supply.  Makes a good emergency power supply for the servos and electronics in fixed wing planes.  If you do this, it's best to use a schottky diode on the esc/ubec 5v power line to prevent voltage backfeeding into the regulator when the main LIPO battery is unplugged.  Personally, I don't bother with the diode - LM7805 regulators don't seem to care about a 5v reverse bias, but your milage may vary...

  • Moderator

    I think that you plug in the secondary battery just before you change the main one? and then turn on the switch, then change packs, then turn off the switch and remove the second pack?

    But you are right the packs will try to balance if they are connected together, I use a different method that is onboard..

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