any merit in running dual battery packs ?

[Keith Black]

Bob, your point about servo performance is true, though I don't how significant it is in our application.

Here's an interesting point that I didn't mention before. With my two packs, one regulated at 5.8 and one at 5.5, after flying four flights the primary 1650 mah  battery will take about 800 mah in charge and the backup 750 mah battery will take about 130 mah. Of the 130 mah I don't know how much is due to the nominal load going to the regulator/RX and how much is actually going to the servos.

I thought this was quite interesting and proved to me that the primary battery is providing the majority of the power. Another thing that this setup does for you is if your backup battery ever requires a larger than normal charge you know something is going wrong somewhere. 

Keith Black
  ----- Original Message ----- 
  From: Bob Richards 
  To: discussion at nsrca.org 
  Sent: Monday, January 24, 2005 2:40 PM
  Subject: Re: any merit in running dual battery packs ?


  The redundant packs also have the possible benefit of improving servo performance. With two packs *and the parallel wiring* you will have less voltage drop and fluctuations when the servos are in a high-load, high-current mode. It is entirely possible that you can be instantaneously drawing several amps current during a flight, particularly during any maneuver where multiple servos will be quickly deflected (like a snap roll). With two packs you have less internal (battery) and external (wiring) resistance.

  I have also noticed that on some servos if you have a 4 cell pack and you lose one cell, the servos will stop working. I know this is true for the first JR super servos. The regular servos continue to operate, although slowly.

  I think there is merit to running two packs.

  Bob R.


  Keith Black <tkeithb at comcast.net> wrote:
    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
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