Re two batteries, was Miracle switch failures

[Earl Vincent]

Keith, the RCA engineer that I mentioned that built my radios back in the 70's and set the battery packs up with the diodes, name 
was Ray Aikins, he was a big scale modeler back then, I have not talked to him in years but he lives in Toms River, NJ. You may
be able to find him on the net. 
  ----- Original Message ----- 
  From: Keith Black 
  To: discussion at nsrca.org 
  Sent: Saturday, March 29, 2003 2:56 AM
  Subject: Re: Re two batteries, was Miracle switch failures


  Bob, that sounds like a good solution. 

  Since the diode consumes some energy what voltage is seen by the receiver? 

  Do you just purchase a diode from an electronics store and solder it in yourself, or is there one marketed specifically for use in our applications (proper connectors etc.).

  Can you share the specifics of the one you use (maybe even a model number and where you purchased it)?

  Thanks, 
  Keith
    ----- Original Message ----- 
    From: WHIP23 at aol.com 
    To: discussion at nsrca.org 
    Sent: Friday, March 28, 2003 5:00 PM
    Subject: Re two batteries, was Miracle switch failures



    Ok third try, I must be e-mail challenged!!



        Hi Guys


          All the "battery backup systems" I have seen put something of unknown reliability/untested in the critical path.  The best setup is two batteries diode orred (sp?) together (diode in each path from switch to receiver) through two switches (must be 5 cell to allow for the diode drop) fully redundant, you would have to have a failure in both paths at the same time to loose control due to battery.  Assuming you check things every flight the odds of a failure in both paths is too remote to consider.  There is little weight penalty, run two batteries 1/2 the size you would normally run.  Being a worrier I also make a point of never running either pack down too far (if I happen to be running on one pack I want enough charge in that one pack to last a long flight).  The diodes must be in the path from the switch to the receiver (if you put them between the battery and the switch, as once got printed incorrectly, with MY name attached, you won't be able to charge in this configuration)  I've been doing this for about 10 years with no problems and it has saved me an airplane, both batteries good on take off one was bad (open) on landing, if only one battery, bye bye airplane.  Guess you could argue that the bad battery might have been in someone else's airplane VBG.  It is a little more complex, two switches (one of the biggest failure items) two charge jacks, two batteries.  Assuming you have an unused channel you can plug the battery into any unused channel (preferred) if not then I would wye it to a non mission critical channel, last choice would be to wye the two batteries together (the wye is then mission critical, I told you I was a worrier)  There is also good evidence that the diodes are not necessary, that a 5 cell pack won't charge a 4 cell pack (one shorted cell), sounds right and I've used this scheme, but I have never tested it with a cell shorted so I have no first had experience.  I'm not sure I could sleep at night, anymore, with only one battery pack and switch, just seems like unnecessary risk.

          Flame suit on, Bye

          Bob








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