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Electrical thoughts

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  • Electrical thoughts

    I am planning on a "no engine driven" electrical system, just a lightweight battery/starter with anticipated ground charging of the battery as required.

    Two paths come to mind.

    1. Lithium battery on firewall, short high current cable to starter solenoid, fused 18G wire to starter switch in cockpit(also runs from said switch to cig lighter jack), second wire from starter switch to solenoid "activation" terminal.

    2. Lithium battery on firewall, short high current cable to "foot activated starter switch" mounted in firewall as used in older Jeeps/tractors(look up a Cole Hersee 9600 as an example), fused 18G wire to to cig lighter jack in cockpit.

    Of course both have appropriate grounds and hot wire from solenoid/switch to starter.

    Neither would have a classic master solenoid and the second would seem to have the weight/simplicity advantage.


  • #2
    I'd probably go with #1 for a couple of reasons. Without a master solenoid, I'd want to limit unfused wire and connections. The high current switch adds wire, corresponding supports and a big metal switch. The high current switch option also adds a bunch of weight, compared to the 'direct to starter' system. Yeah, I know we're not talking about more than a pound, or so, but definitely more weight. Going direct, from the battery to the starter solenoid, then to a (fused) starter switch, seems the lightest and safest, to me.



    • #3
      Many of the Lithium batteries are unstable, over heating and swelling when delivering power and being charged . Study them well. Stinger


      • JimParker256
        JimParker256 commented
        Editing a comment
        There are a lot of differences between various Lithium-based batteries. It's the (now) older-technology lithium-cobalt-oxide batteries that have made most of the news. Like you, I would not be very comfortable with one of those in an airplane, since they can become unstable for no apparent reason.

        The newer-generation LiFe-Po batteries (also known as Lithium-Iron - note the R in the hyphenated part) like the Earth-X series, seem to be much more stable and less prone to the overheating and catching fire issues of the older-generation batteries. (Feels a bit odd to refer to 5-year-old technology as older, but that's the world we live in!)

    • #4
      My thoughts about the foot-operated switch is that if your feet are trying to operate a switch, then they aren't on the brakes. That's the first thing that popped into my head.
      ​Christopher Owens, EAA #808438
      Project "Expedition"
      Bearhawk 4-Place Scratch Built, Plans #991
      Bearhawk Patrol Scratch Built, Plans #P313
      Germantown, Wisconsin, USA


      • JimParker256
        JimParker256 commented
        Editing a comment
        I had the same thought...

    • #5
      Thanks for the inputs!

      Regarding batteries, I have heard good things about Aerovoltz, EarthX and Shorai. Many have built in charging conditioner/protection circuitry and have read a fair number of engine side/firewall mounted success stories.Their Lithium Iron Phosphate chemistry is also not as likely to undergo "thermonuclear meltdown" as "Boeing Lithium".

      Regarding the length of the "always hot" heavy gauge wire run, I could mount the starter solenoid to the side of the battery box(same as one could put a traditional master solenoid) which would keep it under 6" so no difference there.

      Perhaps there is some risk that the starter solenoid could weld itself closed and make one wish for a second inline solenoid but I think that is a pretty low risk.

      But the "high current foot switch" has a certain simplistic appeal and would be even lighter yet. The Cole Hersee 9060 switch(and its equivalents) probably weighs half of the typical starter solenoid plus deletes the panel mounted starter switch.It also doesn't waste any battery current energizing the solenoid.

      However, it would require approximately 16" of additional high current cable and would lengthen the "always hot" run probably 8". It also would require a mounting plate to be welded to one of the firewall frame tubes.

      I thought about the brake point but couldn't think of a time that I started a plane that wasn't already pointed in the direction I wanted to go with at least a few plane lengths of clear space in front.


      • #6
        The "foot switch" doesn't necessarily need to be foot activated. It could be mounted in such a position that lever and push rod could depress it while you are holding the brakes. Just an idea for option 2.


        • #7
          Good thoughts, looking forward to seeing what you come up with. I was considering a similiar setup with ground charging, but will likely go with one of the small B&C gear driven alternators. I'd like to incorperate some small heating elements into the seats for winter ski flying, and will need an alternator to supply adequate power.