Author Topic: External Power Plug 391B  (Read 3216 times)

Bill Miller

External Power Plug 391B
« on: March 23, 2017, 11:21:45 AM »
I see an old cutout, covered over, in the lower left aft cowling on N565JS. I will add a picture next trip to hangar.
I think its labeled too, but maybe this was an artifact of the military paint scheme.
The cutout in the cowl is probably not part of the milspec mods and tribute, though.
Was this possibly an STC or an original option on the type certification? (I can't find any stc or removal note in logs)
Does anyone know how I could either modify or reinstall an external power option.
Usually the third small pin of the 3 pin plug will ground a relay/contactor.
This prevents accidental powering of the cable unless it is connected to a battery or power supply.
We would need to find a drawing of the approved circuit schematic and/or installation instruction.
Thanks y'all
« Last Edit: March 23, 2017, 11:25:23 AM by Bill Miller »

Jason Stephens

Re: External Power Plug 391B
« Reply #1 on: March 23, 2017, 02:52:57 PM »
Both of my projects(U-10B & -395) have the same cutout.  Maybe its a pretty standard item from the factory?  We have a more modern style plug installed on our working airplanes and it is very handy in the event of a dead battery.

Barry Dechert

Re: External Power Plug 391B
« Reply #2 on: March 24, 2017, 08:35:37 PM »
S/N 091 also has the external plug door installed, also the plug installed just was never wired in the system.

Barry Dechert

Re: External Power Plug 391B
« Reply #3 on: March 26, 2017, 07:20:22 AM »
H391B s/n 091 has an external power plug just aft of the right rear passenger door. Military manuals have decent wiring diagrams to reference by. They don't show connection to the small pin I have thought this was used for polarity. Another thing I did not realize is a dual battery installation but from the manufacturer appears it was only utilized with the 24 volt systems. Although in s/n 091 at station 120 (approx.) there had been a base mounted to the first 2 formers in the tailcone, looked very much like a base for an additional battery. Original single battery being installed in the engine compartment. Have a good day!
« Last Edit: March 26, 2017, 07:36:17 AM by Barry Dechert »


Re: External Power Plug 391B
« Reply #4 on: March 26, 2017, 09:07:25 AM »
On H-22 (H800) there is an external power supply plug inside small separate door behind baggage compartment door.  Accepts a 3-prong Cessna plug.  Small prong supplies power to relay solenoid which closes contacts to make circuit to main bus.  Unplugging (or depowering) the external connection opens the circuit thereby making the connector prongs dead.  Since H22 is turbine powered I build an Auxiliary Power Supply Cart to carry a couple of 12 volt batteries (in series) to help with very cold morning starts in New England winter.  It turns out not to be necessary- coldest morning starts with installed battery at +9F. have been successful although others tells me the APU cart makes it easier on installed battery.  Nice then have I have learned to carry the connector and cables on board with me just in case I leave the Master on some day!  (happened once!)  Cheers/ Bob Wallace