Battery or Both

Ventucky Red

Ventucky Red

Pattern Altitude
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When starting your airplane, on the master switch, do you just use the battery to start then flip on the alternator, or both and crank away?
 
Ventucky Red said:
When starting your airplane, on the master switch, do you just use the battery to start then flip on the alternator, or both and crank away?
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Battery only. My alternator doesn't seem to come online if it's on for start. Cycle it, and it's fine, but I tend to just leave it off for start.

Ron Wanttaja
 
You get just the slightest more energy from the battery if the alternator is off.
 
The alternator's field draws two or three amps during start. The starter draws 200 or more. Make of that what you will.

The alternator, during start with the ALT switch on, puts some load on the engine, which is being turned by the starter. Someday, while the alternator belt is loose or off, turn the master and alt switches on and go turn the alternator with your hand. Some effort required. Make of that, too, what you will.

You need to balance the advantages of having the alternator off during start with the risk of forgetting to turn it on.
 
Ventucky Red said:
When starting your airplane, on the master switch, do you just use the battery to start then flip on the alternator, or both and crank away?
Click to expand...

It doesn't make a big difference, so it is a matter of personal preference. I use battery only, and then turn the field on. This allows me to verify the charge/discharge indicator and the warning light after starting.
 
Gilbert Buettner said:
I just use the checklist from the manufacturer.
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This is what created the discussion. Working on an IPC the instructor brought this up when starting the plane. The list says "Master On" to me means both. The instructor says battery, start, alternator, check.
 
Ventucky Red said:
This is what created the discussion. Working on an IPC the instructor brought this up when starting the plane. The list says "Master On" to me means both. The instructor says battery, start, alternator, check.
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I don’t think the checklist is regulatory, it’s advisory. We can adjust as needed.
 
kaiser said:
I do Bat only, then observe positive charging when I click on the alternator after start.
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I think this is where the real difference is - not in what's best for starting, but what's best for confirming normal behavior of your alternator once it comes online.

- Martin
 
With an ammeter it’s pretty darn simple to confirm the alternator is working. The only switch I keep off until after startup is the radio master, and that only in my Cessna. My Cub has a G3X that’s powered through an IBBS backup. I turn the radio master on prior to startup in that plane so the G3X can initialize. The IBBS serves as a power conditioner and prevents a power surge that would cause the G3X to restart.

Know your airplane.
 
kaiser said:
I don’t think the checklist is regulatory, it’s advisory. We can adjust as needed.
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The question doesn‘t seem to be about whether or not the checklist is regulatory, but what the words in the checklist actually mean.
 
What does the checklist say? I've seen checklists call for both, and I've seen checklists call for battery only and then alternator. Most "modern" aircraft call for both.
 
Ventucky Red said:
This is what created the discussion. Working on an IPC the instructor brought this up when starting the plane. The list says "Master On" to me means both. The instructor says battery, start, alternator, check.
Click to expand...
It doesn’t appear that the manufacturer’s checklist says anything about the alternator subsequent to “Master Switch ON,” so I would say the manufacturer is expecting them both to be turned on at that point.

Anything beyond that is technique/airmanship.
 
Generally, Cessna, Beech and Mooney are turn both on, PIper and Cirrus battery only. I was told at one time the difference was if the current from the alternator fed accessories first or the battery first. Don’t know if that is correct.
 
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Mtns2Skies said:
Both, If you leave the alternator on, you will charge the battery while you're spinning the starter. This means that you can crank the engine forever. ;)
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The ultimate in green technology. You could probably get government subsidies for such a device with the current admin....uh...in todays political climate.
 
The only reason I can think of for not turning it on is if the airplane doesn't have a radio master and leaving the alternator off at startup reduces a voltage surge. Modern airplanes should have radio masters so it shouldn't be an issue. Or maybe I'm totally wrong in my assumption. Either way, it works for me.
 
Clip4 said:
Generally, Cessna, Beech and Mooney are turn both on, PIper and Cirrus battery only. I was told at one time the difference was if the current from the alternator fed accessories first or the battery first. Don’t know if that is correct.
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Sounds like some instructor-generated mythology. The alternator feeds the bus, which feeds the battery and everything else. The ammeter tells you which way the current is flowing between the battery and bus. Only the starter current bypasses the ammeter and bus. There is no need for a big ammeter capable of measuring starter current, and if that current went through the bus we'd need a much heaver bus bar.
 
Stewartb said:
The only reason I can think of for not turning it on is if the airplane doesn't have a radio master and leaving the alternator off at startup reduces a voltage surge. Modern airplanes should have radio masters so it shouldn't be an issue. Or maybe I'm totally wrong in my assumption. Either way, it works for me.
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The starter itself generates a large voltage spike when it is released. Much bigger threat than the alternator turning on. Even the starter contactor generates a spike when you release the key. Radios should all be turned off, either with a radio master, or by the radios' switches.

We went through a lot of transponder encoders. They were wired directly to one of the radio breakers, so were on all the time the master was on, and got flashed by the starter and its contactor, and by the master at shutdown. Either they didn't have suppressor diodes, or those diodes just burned out after so many spikes. This was in airplanes that didn't have radio masters.
 
Dan Thomas said:
The ammeter tells you which way the current is flowing between the battery and bus.
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This is generally true for Cessna's. But Piper generally has the ammeter tell you the flow from the alternator/generator to the gus.
Pretty easy to tell the how your ammeter is wired in. if between the bus and battery the ammeter will show a positive or negative flow, showing current going in or out of the battery.
if the ammeter is between the alternator and the bus it will only have a positive values.

Brian
CFIIG/ASEL
 
brcase said:
This is generally true for Cessna's. But Piper generally has the ammeter tell you the flow from the alternator/generator to the gus.
Pretty easy to tell the how your ammeter is wired in. if between the bus and battery the ammeter will show a positive or negative flow, showing current going in or out of the battery.
if the ammeter is between the alternator and the bus it will only have a positive values.

Brian
CFIIG/ASEL
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Yes. Good point that I knew but failed to make. I prefer an ammeter rather than Piper's loadmeter (the correct term for it) since the ammeter will show a definite discharge if the alternator quits on a nice, bright, VFR day, while a loadmeter will go from a very low trickle-charge reading to zero, not a really noticeable movement. The ammeter's movement will be at least double that of the loadmeter.

In the old days, with vacuum-tube radios and motorized incandescent beacons, that loadmeter showed a significant number even on a nice day, but now, with everything transistorized and LED'd, the draws are tiny.

1701881515596.png

1701881627737.png

I like Garmin's way of showing it. A discharge is in red, and the numbers are given in tenths of an amp. At least, that's what I remember from flying a G1000 172 15 years ago.
 
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