any merit in running dual battery packs ?

[ronlock at comcast.net]

I wanted redundancy in the power system for my pattern birds, but without ANY new potential points of failure.   My confinguration is:
Two 700mah 5 cell batt packs.    Each pack direct to a switch, direct to Receiver.
No regulators, diodes, etc.   
I'm more concerned about connector, switch, and solder joint failures in the pack, than failure of a battery cell.  This config gives me redundancy in those areas.
When things go normally, I have 1400mah available with only a slight weight gain over a single larger pack, switch & wiring.

I understand cells more often fail open, than short.   But in case of a short, (the worst case for this config) the good pack must fly the plane, and charge the "bad" pack for duration of the flight.  After research & discussion with others, it's my belief the good pack will tolerate the load of charging the bad one (which won't be at a very high rate) and finishing a flight.  

A potential failure point is me.  (darn humans!)  My duties as crew chief include checking both batts before every flight, and turning on both before flight.

Later, Ron Lockhart
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In a message dated 1/24/2005 7:19:07 AM Eastern Standard Time, hitesh at salt.ac.za writes:
Hi,

Now that we all using high powered digital servo's with incredible holding power etc - is there any merit in running 2 battery packs, say 1 Ah each as opposed to 1 high capacity pack thereby eliminating the single point failure ? If I did want to run 2 packs, is a diode necessary to prevent 1 pack from possibly charging the other if 1 pack were to go bad ?

Cheers,
Hitesh

Hitesh, a 1500 to 2000ma battery is all you need. There's little advantage to redundancy unless you are planning to fly more than 5-7 flights (res) on any given day. But then again, I use NiMH on the airborne and only Sanyo packs, which have proven extremely reliable for several years now.  As such, a redundant power source isn't really necessary in pattern models and you can avoid some unnecessary weight build up. 

What has been done in large models is to add another battery and switch harness to an unused channel on the  receiver, which provides adequate redundancy. The extra weight on such models isn't as critical as it is in pattern models. Both switches "on" at take-off please.

Of course, if you just have to have the extra battery and you have enough weight margin and room, the above is one way to do it. There are other ways, but this is simple and reliable.

MattK
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