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.
Comments
Crasher, any good ESC will not spin up if it receives a high signal when it is powered up. I have the cheapest of the cheap ESC in a little foam airplane, and it just beeps if it gets a signal when you plug it in.
As for my statement that I thought you consider the battery powering your aircraft the least important, it's just based on the fact that you have all these other batteries, but you didn't like the idea of adding one more. It's not a big deal. I totally get your point that with multicopters, adding an extra battery doesn't really buy you much. But every other vehicle, I think it will.
All my GPS guided vehicles had standby power connectors. It's about time standby power got more attention. Another use is keeping the vehicle always powered up on AC, so it can take off at any time, with a full satellite count. The supercaps for retaining ephemeris on those GPS modules never gave the instant accuracy of standby power.
I guess it depends on the aircraft. If you have a multi-copter, yes, any sort of main power failure means you crash. But if you have an airplane or helicopter, both can survive a main power failure, if you can control them.
And in all cases, even multi-copters, having a separate power supply for the APM is safer, as it's easy to power up and let the APM boot with zero risk of having the motors spin up unintentionally, since you can just leave them disconnected until you're ready to go.
Sorry I missed to mention that I put 5x a 1amp diodes in series to have a voltage drop from about 3.5Volt. The discharge voltage of a 3s is about 10V, the fully charged backup Battery is about 12.6V, so 12.6 – 3.5 = 9.1V.
This prevents a charge current to the discharged main battery.
Or if you don’t like the stack of diodes and go the saver way, use a 6sNiMh (~7V) as backup and 1 diode.
In my case it works.
@Crasher, so all those batteries, and the least important battery to you is the one actually flying the aircraft?
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 :)
The diodes on the flight pack will have to handle all that current.
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.
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..