master avionics with engine off?

korben88

korben88

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Troy
I would like to try to diagnose the issue with using my inline gopro audio cable but i don't want to have to burn fuel while I do it.

Is it okay to have the master and avionics on without the engine running?

Cessna 172
 
Yes, you're just draining the battery. How long can you keep them on without ruining the battery? I'm not sure. Someone else will know.
 
Yeah I figured I would drain some battery. But I wouldn't need it for long 3-5 minutes I'd say to get the info I need.
 
A few minutes is likely fine if the battery is healthy, but only really know when you run out of juice when you run out of juice. If you keep lights off and only turn on what you want and don't transmit then power consumption won't be that great.
 
Can you listen to the radio in your car with the engine not running? Same thing!

You can though individually turn off avionics that you will not be using. That will lessen the battery drain.
 
The FBO probably has a ground power unit 'cause people leave master switches on all the time. It's best to do this exercise with one connected. It will probably be fine, but if the battery is a bit weak, it may drain too much to start in 5 minutes. One would hope not, but there are a lot of crappy batteries out there.

If you're powering off a 12V receptacle, why not test it in your car and save a trip to the airport.
 
MAKG1 said:
The FBO probably has a ground power unit 'cause people leave master switches on all the time. It's best to do this exercise with one connected. It will probably be fine, but if the battery is a bit weak, it may drain too much to start in 5 minutes. One would hope not, but there are a lot of crappy batteries out there.

If you're powering off a 12V receptacle, why not test it in your car and save a trip to the airport.
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It's the 1/4" headset plug that I'm having an issue with.

If I had a handheld I could mess around with that I guess. I plan on gettimg one as a backup. Maybe I'll just get one sooner rather than later.
 
For a few minutes, just go ahead and do what you need, turn off everything you won't use. If its gonna take 10 minutes or more with most of the equipment turned on I drag the Astron out and clip it onto the bus.

With a 50 foot extension cord I can sit on the ramp and play without ever using the battery.

One of my favorite tools. Wish I had another one.
 
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Aren't these batteries designed to last a certain amount of time in the event of a generator failure? 5min seems aweful short if I lost one ifr.
 
ifly4fun said:
Aren't these batteries designed to last a certain amount of time in the event of a generator failure? 5min seems aweful short if I lost one ifr.
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On a completely full charge, depending on what you have on, you might get 30-45 minutes out of them I believe.

I had an alternator wire come loose on me once and an alternator die completely. Batteries will keep things running but not for long. I'd rather hook up to external power and "play" then run the battery down to the point where, when I really need it, the power is gone due to me playing around on the ground.
 
Old school lights consume power. Radios will run for hours without draining a battery. After years with an intermittent alternator problem I have plenty of experience with that and I use a very small Odyssey battery. 5 minutes? Not a problem. Don't any of you program digital instruments without the engine running?
 
After an hour or so you battery might be so low that you will have to hand prop to start.
 
Caramon13 said:
On a completely full charge, depending on what you have on, you might get 30-45 minutes out of them I believe.
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I can confirm that to be roughly true for a Cessna 172 that I flew from El Monte (KEMT) to John Wayne (KSNA), only to discover at shut-down that I never turned on the ALTERNATOR side of the master switch. Gahhh. :confused:
 
ifly4fun said:
Aren't these batteries designed to last a certain amount of time in the event of a generator failure? 5min seems aweful short if I lost one ifr.
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Yeah, but the majority of them aren't capacity tested every year. Seems like below 80% and the manufacturer says to replace them despite being able to start the airplane just fine. I've got an 11 year old battery, no it wouldn't pass a capacity test, I don't care either.
 
Turn on the master. Leave the alternator turned off. Besides being a waste of power (3 amps or so for a 14-volt, 60-amp alternator), it heats the field winding in the rotor and can burn off its insulating varnish. Expensive. When the alternator isn't turning it isn't pumping cooling air through itself.
 
ifly4fun said:
Aren't these batteries designed to last a certain amount of time in the event of a generator failure? 5min seems aweful short if I lost one ifr.
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They have a total charge, not a time.

Cranking the engine is the largest load you will put on the battery. Followed by flap motors and radio transmission. Lights and radio reception will work considerably longer.

You can discharge one of these batteries in a few seconds with a "redneck welder." Not recommended.
 
register@teamandras.com said:
I can confirm that to be roughly true for a Cessna 172 that I flew from El Monte (KEMT) to John Wayne (KSNA), only to discover at shut-down that I never turned on the ALTERNATOR side of the master switch. Gahhh. :confused:
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Ya may wanna get in the habit of glancing at the gauges in the airplane every now and then while your flying. Kinda like what's on the checklists.
 
MAKG1 said:
They have a total charge, not a time.

Cranking the engine is the largest load you will put on the battery. Followed by flap motors and radio transmission. Lights and radio reception will work considerably longer.

You can discharge one of these batteries in a few seconds with a "redneck welder." Not recommended.
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And use a glove. The welder gets hot.
 
I turned mine on for the grandkids to sit and play with the controls while "talking" to the ATIS on their headsets. Had it on for about ten minutes while I showed my son around the plane and hangar. No issue with the next time I started it up.
 
I have a G1000 so it eats up the battery pretty quick with all them new-fangled screens. I frequently turn on my battery and master for several minutes while updating my nav database and other G1000 databases. Never an issue. Its not long enough to drain the battery to a considerable amount to not at least be able to start the engine up. As someone else said though I'm sure some FBO on the field has a GPU to be able to provide your plane battery if you need the stuff turned on without the engine for an extended period, or to start the engine up!
 
JustinD said:
I have a G1000 so it eats up the battery pretty quick with all them new-fangled screens. I frequently turn on my battery and master for several minutes while updating my nav database and other G1000 databases. Never an issue. Its not long enough to drain the battery to a considerable amount to not at least be able to start the engine up. As someone else said though I'm sure some FBO on the field has a GPU to be able to provide your plane battery if you need the stuff turned on without the engine for an extended period, or to start the engine up!
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The screens are not at all bad compared to electric gyros. Your G1000 doesn't have any. Almost all IFR certified six-packs do.

It only takes about a minute to update both nav databases. And one side can be done on the standby battery, which doesn't eat main battery charge.
 
SkyDog58 said:
Can you listen to the radio in your car with the engine not running? Same thing!

You can though individually turn off avionics that you will not be using. That will lessen the battery drain.
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Apollo 13 scenario. :D
 
MAKG1 said:
The screens are not at all bad compared to electric gyros. Your G1000 doesn't have any. Almost all IFR certified six-packs do.

It only takes about a minute to update both nav databases. And one side can be done on the standby battery, which doesn't eat main battery charge.
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G1000 uses 9 amps just to run the PFD and one com, with the MFD and transponder off. Essential bus stuff. That's what it indicates when we do the annual 55-minute standby battery test. There aren't any gyros that eat 9 amps. An electric T&B or TC uses maybe two amps at most. The other gyros are usually vacuum- or air-driven.
 
All depends on the condition (age, usage etc) of your battery on how long it will last if you lose an alternator and/or alternator belt. I always teach students to check the alternator belt during preflight. One of few things you can check without taking the cow off.
 
Just keep a eye on your voltage, if you're looking to really start playing with all that stuff hook a GPU up.



Capt. Geoffrey Thorpe said:
After an hour or so you battery might be so low that you will have to hand prop to start.
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Or bump start it, probably not the nicest thing to do to the starter, but on a three blade, or on the water
 
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