Funny you should mention that. That's what I use as a master switch (this one is a round one with a red plastic "key"), mounted directly on the battery plus terminal. No master contactor (solenoid) to drain the battery. I usually leave it on when not tied down at home and always get helpful comments about how I've left the power on (engine monitor warning LED is lit). But actual power draw between my EM and handheld Icom and GPS is well less that 0.5 amp. Can sit there 1/2 day and still no problem starting.

And yes it is very convenient when fiddling with engine, starter, etc. to be comfortable that there is no power out there to be shorted to ground.

Finn

Paul wrote:

Hi, Mark....unfortunately, I am presently working as a heavy truck mechanic (18 wheelers), and I have been on many a road call where the starter was stuck engaged.On a few units, once I disconnected the batteries (4 of them) the starter would be OK to use again. On two of the trucks, I could not get to them in time, and it burned the wiring harness so badly that the whole harness had to be replaced. The other tractor burned to the ground. Melted all the tires, all windows gone, all fiberglass hood and fender parts melted....not a pretty picture.
I have a quick disconnect on the negative terminal on my motor home so that if the starter solenoid should hang up, I can simply open the blade-style switch and disconnect the battery. Hopefully I will never need it, but it's nice to know it's there just in case. I have been looking at the various battery switches/quick disconnects at West Marine, and have been considering one for my aircraft. Heck, it's convenient jus to be able to quick-disconnect the battery when working on the panel, fuel pumps, spark plugs/wires, etc. Just a thought. Paul Conner

    ----- Original Message -----
    *From:* Mark R Steitle <mailto:mark.steitle@austin.utexas.edu>
    *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
    *Sent:* Monday, January 24, 2005 8:47 AM
    *Subject:* [FlyRotary] Re: Battery load test

    Wendell,

    There is some benefit to using a starter relay in addition to the
    starter solenoid. The argument is that this arrangement will keep
    the fat wire going to the starter from being always hot. Also,
    I’ve heard stories of starter solenoids sticking with no way to
    stop the starter until it runs the battery dead. Not sure I buy
    that argument though. I tied my alternator B+ wire to the battery
    terminal on the solenoid (mounted on firewall) rather than
    running it all the way back to the battery (in the tail). I also
    picked up on the same B+ terminal to provide power to the Main
    Power Buss. This saved about 25’ of heavy gauge wire, offsetting
    the weight of the solenoid.

    Mark S.

        Refering to the battery going directly to the starter, most
        all starters with built in solinoids are so wired. I remember
        having a starter to hang on occasion and drain the battery or
        ruin the starter. Is it practicle to use a relay in
        conjunction with the starter/solenoid set up?

        Wendell

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