[NSRCA-discussion] FW: Switch /replacement/reliability

[John Pavlick]

----- Original Message -----
  From: John Pavlick
  To: ronlock at comcast.net
  Cc: jpavlick at idseng.com
  Sent: Friday, June 16, 2006 3:29 PM
  Subject: Re: [NSRCA-discussion] Switch /replacement/reliability


  Ron,
   You can forward this to the list - I'm at work so I can't do it myself.
This is the system that I have: I'm using 2 heavy duty switches and one 2/3A
4-cell NiMH pack with 2 leads. The cells have very low internal resistance
(7mOhm) and the 4-cell pack only weighs about 3 ox. The one part that people
overlook is the switch. THAT is probably the most unreliable part AND it
factors into the "resistance" parameter if it's used in line (not true with
a "fail-safe" type). Even a good switch adds some resistance. By using 2
switches, you minimize the resistance AND you add reliability. It adds a
little weight, but not much. I plug the second switch into an unused
receiver "channel". Another advantage to this setup is that it allows you to
measure the battery pack voltage when your radio is on OR with an ESV in the
conventional way. The ultimate system in terms of reliability is of course 2
packs + 2 switches, but a good compromise can be reached by using a
dual-lead 5-cell pack with the 2 switch setup. Usually when a cell fails, it
looks like a short. No voltage out, but the other cells can conduct current
through it. Your pack voltage drops to slightly less than a good 4-cell pack
(because you still have 4 "good" cells working) and you can still land the
plane. I check my batteries before and after each flight and I top them off
before each flight with a Sirius charger. I use 4-cell packs on my current
airplanes to save weight and because I have Futaba servos in one of them,
but 5-cells are better in most cases.

  John Pavlick
  http://www.idseng.com

  Ron Lockhart <ronlock at comcast.net> wrote:
    Here is another candidate for switch reliability.

    One battery with two leads each to a switch, each lead from switch to
RX.
    If you can remember to turn on two switches (or mechanically tie both
switches to a single
    mechanical actuator) you get redundant switches and connectors to RX.
    Zero additional single point failure items, not heavy or expensive.

    If you want to add battery redundancy; Two batts, each to it's own
switch, each with
    seperate cable and connector to RX.
    You have to accept additional workload of checking both batteries often.

    Later, Ron Lockhart

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