Stupid Question about Jump Plugs

Discussion in 'Maintenance Bay' started by AA5Bman, Feb 12, 2020.

  1. AA5Bman

    AA5Bman Pre-takeoff checklist

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    I have a 12V Cessna with the external power receptacle just forward of the pilot's side door. I recently bought one of those little jump packs for emergency use. Do I need to buy one of these as well?

    https://www.aircraftspruce.com/catalog/elpages/plugnjump.php

    I have always assumed that the answer is yes, but I find myself wondering if I really need a nearly $100 interface to go between the plugs and the... other plugs. If I can reach with my alligator clips, can I just go directly to the external power receptacle? If not, is there a less expensive version? (the "cessna" version, amazingly, costs less - $37.50 - but won't take alligator clips).
     
  2. bnt83

    bnt83 Final Approach PoA Supporter

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    You'd be better off with a plug that will securely connect everything unless you don't care about the clips falling off and shorting out your jump pack.

    In the 12 years I've been flying, I've needed a battery once, local guy let me borrow his. I have never used the ground power plug and some of them are probably broken to boot.
     
  3. NordicDave

    NordicDave Pattern Altitude PoA Supporter

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    Also check the POH and service manual wiring diagram. The articulation of the external plug purpose has changed over the years for various models. Some are for jump starting and other years for powering the electrical system for ground testing.

    It's never a good idea to jump start an aircraft, though many do. The battery does speak when it's in its waning months of service. A pilot on my last field had his battery explode with a jump start. Not common, but does happen. It was not a pretty sight. He was trying to stretch his battery life a few more months, and for what end?

    If the plane was sitting, much better practice to charge the battery first.
     
  4. Bill Jennings

    Bill Jennings Touchdown! Greaser! PoA Supporter

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    The 172 I used to club fly had instructions in the POH to leave the master off when jump starting via the external power plug. Evidently that plug sends power to the starter solenoid directly bypassing the master. The Mooney has a similar plug, but it's been so long since I've read that section of the POH that I can't describe it's proper use.
     
  5. lsaway

    lsaway Pre-takeoff checklist

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    There are 3 terminals on the external power receptacle, 2 are + 12v, 1 is ground. Your jump box only has 2 leads, so you would have to make your positive clip connect both +12v pins simultaneously. The receptacle is so small, it would be impossible to get your alligator clips onto the correct pins without shorting to each other, or to the aircraft frame, which is very bad either way. If you did have small enough alligator clips to do that, they would not transfer enough amps to start the engine. Don't even try it, its not worth the risk. The plug adapters connect both +12v pins together internally in the plug, which will activate the external power relay.
     
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  6. chartbundle

    chartbundle Cleared for Takeoff

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    Jim Carpenter and 3393RP like this.
  7. AA5Bman

    AA5Bman Pre-takeoff checklist

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    Thanks - this is what I needed, I’ll pony up the dough (as usual!).

    Yeah, I’m aware of the issues with jumping planes. Had to do it once and man it was a relief. This is really only for use in remote places where there is no help or services - part of my emergency kit.
     
  8. NordicDave

    NordicDave Pattern Altitude PoA Supporter

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    You're bringing up a good proof point. The behavior and circuitry for the external power plug has changed over the years and between models. There is no consistent functionality. Some have also been rewired as battery charger port or to operate like a different model or model year to suit that owner.
     
  9. RSFTucson

    RSFTucson Filing Flight Plan

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    I have one of those. Never used.. or maybe once. with shipping its yours for $45.00.
    Let me know, and I will email you my address, for your mailing / shipping address.
    randalforbes@gmail.com
     
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  10. frfly172

    frfly172 Touchdown! Greaser!

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    There is an option to get a pair of jumper cables with the plug in attached .