any merit in running dual battery packs ?

[Hitesh Gajjar]

Hi Keith,

I don't receive the K-Factor - different country - so I'm not familiar with
Lance's approach ? I'm interested in the voltage regulators you using - are
they DIY or off the shelf ?
After a good flying session, have you tested the capacity of both battery
packs to get a feeling of what's actually happening in flight ie. is the
2'nd battery pack being used during high current loads, somewhat unexpected
but entirely possible ?

Cheers,
Hitesh

  -----Original Message-----
  From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On
Behalf Of Keith Black
  Sent: 24 January 2005 09:26
  To: discussion at nsrca.org
  Subject: Re: any merit in running dual battery packs ?


  Though it's true that most planes flown use only one battery, and if
maintained correctly a pilot can go years without loosing a plane for power
reasons if he's lucky, there are still several failure points that can turn
a two to three thousand dollar model into firewood. I personally know of at
least four pattern planes that have been lost due to power issues. The
failure points include bad wiring, faulty regulator (if used), switch,
battery going bad, false peaks, battery becoming dislodged and unplugging,
and probably some others that I haven't thought of.

  I think having a backup battery is a very good idea if you can afford the
additional weight. I personally prefer the second battery even if it makes
me a few ounces over weight for the majority of my flying which is practice.
A centrally located backup battery can be removed for contests to make the
weight limit.

  A backup battery can be done as described in Lance's article in the
December K-Factor or there are other approaches that can be used. The method
I use is two five cell packs, one primary (pick your battery type or size)
and one a AAA 750 mha NiMH pack, both going through their own switch and
regulator into different channels in the RX. The regulator on the primary
battery is 5.8 volts and the regulator on the backup battery is 5.5 volts.
This will cause the voltage to be drawn from the primary battery and not the
backup battery. Voltage will only be pulled form the backup battery when the
primary battery voltage drops below 5.5 volts. The regulators also perform
the task of preventing reverse charging (like a diode).

  This approach is slightly heavier than Lance's approach since it requires
two regulators and an additional cell, but for me it worked well and was
easy.

  Keith

  ----- Original Message -----
    From: Rcmaster199 at aol.com
    To: discussion at nsrca.org
    Sent: Monday, January 24, 2005 10:16 AM
    Subject: Re: any merit in running dual battery packs ?


    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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