EXTERNAL PWR with MASTER/BATT SWITCH?

What's the reason, most of the certified aiplanes do not allow connecting the External Power Src without turning the MASTER / BATTERY contactor ON?

.. battery protection?

I don't know, but would guess that the power connection is downstream of the contactor and closing it (i.e. putting the battery into the circuit) provides a great deal of protection. The battery is like a massive capacitor and will absorb many spikes and other bad things that can be introduced by an external power supply.

Larry

I would assume this is specifically for "jump start" connections. So just like your car you jump the battery, start the engine and disconnect the external power.

I offer that such clunky external jump start connections are a relic of pink weenie batteries on 1960s Cessnas and have no place in our RVs. Jumping a dead battery is not how you want to launch with a glass panel. Recharge or replace the battery.

For running the panel on the ground a simple jumper to a ~30 amp power supply is perfect - and will charge the battery(s) if needed.

Carl

Carl Froehlich said:

..

Jumping a dead battery is not how you want to launch with a glass panel. Recharge or replace the battery.
..

Carl

Click to expand...

That's the point. With how it's wired, you cannot recharge the battery without switching MASTER ON (connecting the BAT Contactor and the EXT PWR Contactor) at the same time.

Btw, the latest SR22 has the same wiring.. only for 'jump start' in cold days, no battery recharge through the EXT PWR socket.

-Is there anything wrong to wire it the way that the external power closes the EXT PWR Contactor as soon as it's connected -provided the OV protection is intact? It would connect directly to the ships main battery.

Over voltage is one concern. The other is reversed polarity which could destroy avionics.