Hi guys,

I have read in some other places, that people use two battery packs on the same Rx!! How is this possible?? Lets say I have 2 NiCd packs and they are connected to 2 different switches!! The output of one switch goes to the battery channel of the Rx.. Where does the other switch's output go to?? Theoretically I can plug it onto any free channel to power the Rx, but will that not fry the Rx if I give power inputs from two different 6V sources??

Someone with more experience please elaborate on this topic.. I tried googling around for some time but was highly unsuccessful today!!

I am thinking of this mainly because, if I have a failed battery then the other one can take over making it a redundant power supply..

- Chan

Chan,
I have used this setup earlier, as a failsafe on my more expensive models.
On most Futaba receivers you can plug in as many batteries as you want ( of course the same voltage ), on spare RX channels.
Basically the RX channels have 3 connectors, the +ve and the -ve and the singal channel.
The +v and -ve on all channels are wired to the main bus, thereby if one battery fails the RX will not know and the current from the second battery would get used.
On my gasser, i will use 2 batteries, each connected with a switch, and then the leads from these 2 switches connected to 2 channels on the RX.

Hope this helps.

Gaurav's method will work perfectly and it is more than adequate for our RC use.

However, if you really need a bullet proof system then you need an elimination/change-over  circuit, where the weaker battery is eliminated from the circuit and the other healthy battery powers the system. That requires a circuit.

In Gaurav's method, the healthy battery will be powering the RX and re-charging the weaker battery pack as well. Not an issue for our 10 to 20 min flying.

Thanks a lot Ismail and Gaurav.  It clears up a lot of things for me.  I was infact expecting a reply from Ismail for both my threads started today!! And I got it on both !!

Gaurav.. thanks again..

- Chan

Gaurav's method is NOT recommended. Simply because the "stronger" battery will feed part of it's output into the "weaker" one.

If a two (or more ) battery set up is needed for any reason, then each of them should have a diode in series with the output. This, however, would need a 5 cell (6 volt) pack as there is drop of approximately 0.6 V in the diode.

The diodes would have to be in a Y harness. Otherwise you would not be able to charge the batteries.

Quote from: sushil_anand on July 31, 2009, 04:30:36 PM
Gaurav's method is NOT recommended. Simply because the "stronger" battery will feed part of it's output into the "weaker" one.

If a two (or more ) battery set up is needed for any reason, then each of them should have a diode in series with the output. This, however, would need a 5 cell (6 volt) pack as there is drop of approximately 0.6 V in the diode.

The diodes would have to be in a Y harness. Otherwise you would not be able to charge the batteries.

Well you are correct in the part about the stronger battery charging the weaker battery, but if you have a high mah pack, and fly for a short duration, then it works like a charm. I have used this setup in my extra .90 and it works without any problems. It is important that the 2 battery types should be of the same chemistry, and similar voltage/capacity.

Diode setup should be ok, but even without it, it works .

Diodes.. thatz what I meant by a circuit! 

Without diodes also it should work. Probability for failure is very low... but diodes will eliminate that small failure probability as well.

Battery packs can be put on any free channel on the receiver. It is just the equivalent of having a parallel pack external to the receiver sans the connectivity issues. the mah value gets added and all other parameters remain the same and provides a fail safe mechanism as well. Works well without any circuit or diodes.......
Edwin

This is useful for those who are planning to use diodes on their setup.
http://www.eaavideo.org/video.aspx?v=713336874001