M20E Backup Electrical System

[AH64Bennett]

I’ve got a 1965 M20E with full Garmin glass, G3X, G5, GTN650xi, GFC500, GTX345 remote, GNC 215.  I’ve have the  the PlanePower alternator system installed.  This last weekend over 4 hours of IMC in precipitation I saw the ALT light flash twice.  Currently having the belt tension adjusted but that got me thinking about a second electrical system.  Has anyone installed a second battery, second alternator… etc.  I love the systems and am wondering the possibilities for redundant electrical.

[KSMooniac]

You have a couple of options, assuming you deleted the vacuum system with the panel upgrades.  B&C makes a nice little alternator that lives on the accessory drive pad where the vacuum pump resides.  It is STC'd for some applications, but I don't believe Mooneys are on the AML yet but I've read many accounts of easy field approvals for it since it is a safety enhancer.  TCW has STC'd backup battery systems for many planes including Mooneys, and you can install it in several different ways.  I have one of their systems to back up my dual ElectroAir electronic ignitions where it is wired to my #1 ignition and nothing else.  They have schematic examples of different ways to connect it to a panel and I believe it would be pretty straight-forward to have it run a couple boxes, such as your GTN and GFC500, assuming you already have backup a battery on the G5 and perhaps G3X.  Wiring integration of the TCW system will be more extensive than the B&C.

[PT20J]

Check the actual current draw and the Ahr capacity of your battery. My similar panel will run for 2 hrs on the ships battery. 

[AH64Bennett]

I have removed the vacuum system, so a vacuum pump replacement alternator would be nice.  I have the battery backup for G5 but not G3.  I’m pulling around 9 amps full power.  The ALT light in precipitation flashed with incandescent landing light, torpedo “burn your hand” interior lights, led nav lights and panel running.

[JoeM]

My first thought would be to replace the incandescent landing light with LED. That should reduce your draw by several amps. 

[cliffy]

First your main ship's battery is your "backup" power supply in case of an alternator failure

It is vitally important to know how good your battery is and how long it will power your systems

Do you do an annual battery capacity check? If not DO IT!

Most IFR rated Mooney owners who actually fly IMC DON"T do it --BIG MISTAKE!

A secondary power supply is not a bad idea IF you do lots of IMC work. If not -an alternator failure is a bonified emergency declaration.

How long do you "think"  it will take you to get down if IMC?  Now double that estimate. DO you have enough battery capacity to do it?

If you do suffer an alternator failure have you given any thought to how you will download the electrical system to save battery power until you land? 

Turn off all not needed equipment. Pull breakers if necessary. What do you absolutely need and nothing more.

Turn off all outside lights (EVEN at night) you don't need them in an emergency. 

As far as the battery goes,  just because it started the engine for this flight doesn't mean it will power the airplane for an hour

Starting the engine actually takes very little of the battery capacity so a bad battery can and will start the engine. 

Have you ever come out to your airplane and tried to  start it and it only grunted. Dead battery. How much capacity do you think it had on the last flight if you had a generator failure?

Don't even think of jump starting a dead battery and charging off into IMC conditions

Most  battery manufacturers say it takes 3 or more hours of continuous flying to to fully recharge a dead battery

Where will you be if 15 mins after takeoff the alternator quits?

The same goes for VFR flights  -  No jump starting and flying-- its always a bad idea. 

 

 

 

[AH64Bennett]

I have not done an annual battery capacity check but you’re right.  I fly a lot of IFR, usually 10 - 15,000.

The backup system is part of a larger plan for a solo circumnavigation.  The wiring and the panel has been done.  I had the long range tanks installed in July.  I really want redundancy for crossing the Atlantic but even more so for the Pacific crossing.

I like the idea of the B&C alternator, thank you @KSMooniac.  I’m going to see about obtaining a 337 approval to add one in place of the vacuum pump.

[cliffy]

Earth Rounders Club ?  :-)   @AH64Bennett      Check out Honey Mooney website.

He came through my home drome a few years ago.