APU start with a low battery
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Joined: Mar 2009
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From: USA
It may decrease the life, not sure if it could creat a runaway scenario on a sick battery. I would not let it worry me one bit though, you are doing far more damage to your apu (longer hotter spool times).
Joined: Aug 1998
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From: Ex-pat Aussie in the UK
How hard the battery works affects the amount of heat it generates. The thermal profile of a battery affects its cycle life.
On the 737 (-300 at least), as well, if the battery voltage falls below 18V during the APU start, several of the relays in the start sequence can fail to operate, which can have unexpected electrical effects.
On the 737 (-300 at least), as well, if the battery voltage falls below 18V during the APU start, several of the relays in the start sequence can fail to operate, which can have unexpected electrical effects.
Joined: Oct 2005
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From: USA
As checkboard noted, the battery is largely inconsequential in light of the potential damage to the APU. If the battery voltage is low, slower spool up times for the start will occur, and potentially hotter starts may occur.
A low battery results in longer starter engagement times, and potentially the inability to spool the engine fast enough.
A battery which has been drained will take greater current when receiving a charge after the start, which can result in higher batter temperatures. In the case of NiCad batteries the potential for a thermal runaway exists...which definitely does damage to the battery...as well as the surrounding airframe.
A low battery results in longer starter engagement times, and potentially the inability to spool the engine fast enough.
A battery which has been drained will take greater current when receiving a charge after the start, which can result in higher batter temperatures. In the case of NiCad batteries the potential for a thermal runaway exists...which definitely does damage to the battery...as well as the surrounding airframe.
Joined: Jan 2002
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From: Brisbane, Australia
This just got me thinking...
in the 737NG, with a low main battery, trying to start the APU,
just thinking, when standby power is activated is the only time the main and standby batteries are connected electrically!
so, will activating standby power help in this situation by increasing the capacity, and therefore the voltage, of the power source to start the APU?
just a thought...FD
in the 737NG, with a low main battery, trying to start the APU,
just thinking, when standby power is activated is the only time the main and standby batteries are connected electrically!
so, will activating standby power help in this situation by increasing the capacity, and therefore the voltage, of the power source to start the APU?
just a thought...FD
Joined: Apr 2009
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From: Wherever it is this month
I'll add another vote to SNS3Guppy's point: starting the APU with a drained battery can lead to excessive charging current immediately post-start. On my type this can lead to boiled electrolyte and a resulting acid-spill mess...
Joined: Feb 2004
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From: Australia
just thinking, when standby power is activated is the only time the main and standby batteries are connected electrically!
so, will activating standby power help in this situation by increasing the capacity, and therefore the voltage, of the power source to start the APU?
so, will activating standby power help in this situation by increasing the capacity, and therefore the voltage, of the power source to start the APU?
Ref: AMM D&O 24-31-00
Rgds.
NSEU
Joined: Feb 2004
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From: Australia
Modern aircraft should have a battery temperature sensor circuit which will disable the battery charger if the internal temperature of the battery gets too high. Also, they should have sophisticated charging control circuits to prevent excessive charging currents and to help prevent thermal runaway.
The battery will not be recharged if the voltage (of the battery) is too low.
Boeing aircraft, including the 737NG, have these features.
Rgds.
NSEU
The battery will not be recharged if the voltage (of the battery) is too low.
Boeing aircraft, including the 737NG, have these features.
Rgds.
NSEU
Joined: Aug 2009
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From: South of N90º00'.0
Most all of the aircraft I've flown had minimum battery voltage requirements for APU Start or Engine start (when applicable). Why would you guys want to start the APU when the voltage is outside of the published (Approved) parameters?
Joined: Apr 2005
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From: Stockholm Sweden
On the A330 the APU battery is disconnected when it falls below 23V. You can't start with a flat battery. But Airbus, unlike Boeings that I know, will start the APU from ground power.
And during an APU start, the battery will disconnect at 9-12V remaining.
And during an APU start, the battery will disconnect at 9-12V remaining.
Last edited by Swedish Steve; 10th April 2010 at 16:18.
Joined: Apr 2005
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From: Stockholm Sweden
I have been thinking about the B737 Classic starting off ground power, and I can't see how it works.
I remember, many years ago having a B737-200 with a flat battery. We used a DC ground power unit plugged into the E and E bay and started the APU. We were in a hurry to get it up the ramp.
But other times, on the line with a flat battery, I have plugged in AC ground power and charged the battery until it has enough volts to start the APU. I have never tried to start a B737-400 APU off AC ground power.
Now I need to hunt out a maint manual.
I remember, many years ago having a B737-200 with a flat battery. We used a DC ground power unit plugged into the E and E bay and started the APU. We were in a hurry to get it up the ramp.
But other times, on the line with a flat battery, I have plugged in AC ground power and charged the battery until it has enough volts to start the APU. I have never tried to start a B737-400 APU off AC ground power.
Now I need to hunt out a maint manual.
Joined: Jul 2008
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From: Skating away on the thin ice of a new day.
steve,lem,flt detent
Steve..
Classics can have a dc plug in the e&e for an external supply.
LEM..
Starting an apu with a low battery can be risky.
Sure the battery will suffer but the apu is at greater risk.
flt detent..
Not across all variants but the NG's I am familair with (-800's) have just the one battery for powering the buses.(barring the backup in P6 to close some valves )
Classics can have a dc plug in the e&e for an external supply.
LEM..
Starting an apu with a low battery can be risky.
Sure the battery will suffer but the apu is at greater risk.
flt detent..
Not across all variants but the NG's I am familair with (-800's) have just the one battery for powering the buses.(barring the backup in P6 to close some valves )
Thread Starter
Joined: May 2003
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From: The Roman Empire
Apart from the DC plug connection in the E&E bay, the 737 classic (300-400) will start also from normal AC external plug... I was puzzled too the first time that happened to me, because one would think, reading the manuals, that it doesn't, but it does start the APU like that!!
Joined: Jul 2008
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From: Skating away on the thin ice of a new day.
The 737-300 and 400's I have worked on (many dozens) cannot start the apu using a.c. power.
In normal service they all must have a battery connected and (relatively) serviceable.
The battery is charged using the a.c. via the charger but there is no facility to start directly from a.c. on the classics I have worked on .
It has a d.c. starter only.
The new gens are a different story.
In normal service they all must have a battery connected and (relatively) serviceable.
The battery is charged using the a.c. via the charger but there is no facility to start directly from a.c. on the classics I have worked on .
It has a d.c. starter only.
The new gens are a different story.
