Can the battery be switched off when the engine is running?

[CCairns10]

Because the alternators will do the battery's job for it, like the dynamo in a motor car. I've never tried switching the battery off during flight because I'm too proud to crash! Also don't the alternators recharge the battery when they're running?

Chris

[mmm6262]

Correct, you can turn the battery off after the engine is started and the engine will NOT quit. You can even turn off the alternator. The engine just depends on the battery for startup. And yes the alternator will keep the battery's charge. This is at least true for single piston planes. Hope this helps.

Happy Flying
Gabriel Molina

[CCairns10]

Hi Gabriel

Isn't the alternator required to provide electricity for the instruments and lights? does a piston engine have spark plugs and that means it needs electricity? For these reasons I thought it would be very dangerous to turn off the alternators.

Chris

[rtriez]

Yes, a piston engine has spark plugs, two per cylinder if I'm not mistaken. But the spark is produced by a magneto, much like your lawn mower. Once it's started, there's no external power sourse to power the ignition system. The alternator simply recharges the battery. If you turn the alternator(s) off, the lights will still funtion until the battery goes flat.

Hope this helped some :)






Best Regards,

Bob :-wave

[link:www.voyagerairlines.com/gle/index.html|http://www.flightsim.com/dcforum/Use...e72514cf2.jpg]

[CCairns10]

I wonder how magnetos work? the magnetic field they produce must interact with the movement of the cylinder thus producing an electromagnetic electricity thus creating a spark, this is probably nonsense but I can't think how else they work, I'll need to look up the help menu in FS2002.

Chris

[Buffdhc5]

They have several coils inside that generate an electrical charge that is dissipated when a set of point open. The magneto is driven buy the camshaft on the engine. So yes the movement of the pistons inside the engine does have something to do with it.

[flyinggriffin]

Yes you can turn off the alternator and everything runs.....for a while. In the winter with pitot heat all the lights on and radios working you may get as little as 15-30 minutes of power. It all depends on how much amperage you are using. I had the circut breaker on the alternator die somewhere on climbout on me. There is a lot of electrically powered devices in a plain vanilla Skyhawk. It can suck the life out of the battery in a hurry if you arn't careful.

The magnetos are driven off off the engine via a geartrain in the acessory case lots of times in the rear of the engine. Some engines have both mags driven by the same system, others give each of the mags their own drivetrain.

The battery functions much like the air storage tank on a compressor so that enough amperage is available when you draw a heavier load than the alternator is capable of delivering. If you run the battery down too low, the alternator will cease to function. It needs a certain voltage to excite the field in order to function. In other words, if you think you can hand prop the engine to start it and charge the battery that way, you are in for a suprise.

Generators do not have this problem, but they are heavier, and are not very good at low rpms. You could find yourself running low on juice waiting to take off if you had used a lot of the battery up in starting getting to the runway.

[Matt]

[font size="1" color="#FF0000"]LAST EDITED ON May-16-02 AT 11:01PM (EDT)[/font][p]just to clear up a issue: You can turn the alternator off without turning off the battery. you can't, however, turn off the battery and still let the alternator run.

Magnetos are driven by the camshaft. The camshaft drives a magnet inside the magneto "box". Magnets have magnetic lines of flux. These magnetic lines of flux are being "cut" by conductors which produce electricity. Coils are then put into place to drive up the voltage and lower the ampers (so that a spark may be produced at the spark plug). This is just a simple explanation.


Anyhow, lets move on to the battery's life.

I did a project for my class about how long the battery lasts if the alternator quits and all non essential equipment is turned off. Aircrafts included in this porject were the C152, C172R, and C172RG.

I copied a small part from my project in here just FYI. If anyone wants to know how i came up with these numbers i'll give you an explanation.


Cessna 152.
Systems included in the calculation: beacon, inst light, radio1, radio2, transponder;
Rated ampere-hour of battery: 35 amps/h
Maximum current flow possible (Load): 35 amps/h
Theoretical useful life of the battery: 37 minutes 30 seconds

Cessna 172.
Systems included in the calculation: inst, T/C, inst light, fan, nav/com1, transponder, beacon;
Rated ampere-hour of battery: 12.3 amps/h
Maximum current flow possible (Load): 48 amps/h
Theoretical useful life of the battery: 9 minutes 37 seconds

Cessna 172RG.
Systems included in the calculation: beacon, inst, transponder, nav/com1, inst light, fan, T/C;
Rated ampere-hour of battery: 35 amps/h
Maximum current flow possible (Load): 46 amps/h
Theoretical useful life of the battery: 28 minutes 32 seconds

[ladamson]

Checking out new camera. Compressing from over 2 million bytes to under 100,000. The mags are the two black units on the back of engine. Right side of pic. Lycoming 0360

http://www.flightsim.com/dcforum/Use...5d718ac810.jpg

Ladamson

[CCairns10]

Magnetos sound like spark plugs that don't need a battery as long as the engine is running to drive them, but still needs the battery to start it, like everything else. With the advantage stated, I wonder why they are not used in motor cars? Too bulky?

Chris