757 Electical technical question
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Originally Posted by b44
I believe the clock load on a 757 is similar to the drain on your car battery. The clock draws miliamps so a good battery should still be good for 6 months to a year.
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A non ER 757 main battery will give you 30 minutes of power (40amphours). On a ER version, you also have the HMG, which powers the hot batt bus for unlimited time, thus the battery will be charged all the time.
For the EICAS msg you had, it shows the charger is defective. If the message is followed slightly later by the main batt disch message, you know the battery will be dead within 30 minutes.
@oceancrosser, the charger message will most likely be a charger, and not the battery. The charger has protective shutdowns built in, e.g. with an overtemp batt, which of course go away if you put a new battery in. Question is, how long before your defective charger eats up the newly installed battery...
For aircraft storage/prolonged parking, we disconnect the batteries from their busses. Also be aware that some solenoids do eat battery power, as some solenoids are energized when the cockpit switch is off. It doesn't mean that when a pilot switches a system off, that it is completely removed from the battery.
And as said the hot batt bus has no switch, it is directly connected to the main battery and its charger. The hot batt bus is in turn connected to the ground service bus, which gets power from either a GPU connected + ground service switch pressed (batt charging on ground), or from the right AC bus (batt charging in flight).
For the EICAS msg you had, it shows the charger is defective. If the message is followed slightly later by the main batt disch message, you know the battery will be dead within 30 minutes.
@oceancrosser, the charger message will most likely be a charger, and not the battery. The charger has protective shutdowns built in, e.g. with an overtemp batt, which of course go away if you put a new battery in. Question is, how long before your defective charger eats up the newly installed battery...
For aircraft storage/prolonged parking, we disconnect the batteries from their busses. Also be aware that some solenoids do eat battery power, as some solenoids are energized when the cockpit switch is off. It doesn't mean that when a pilot switches a system off, that it is completely removed from the battery.
And as said the hot batt bus has no switch, it is directly connected to the main battery and its charger. The hot batt bus is in turn connected to the ground service bus, which gets power from either a GPU connected + ground service switch pressed (batt charging on ground), or from the right AC bus (batt charging in flight).
Last edited by Piper19; 8th Sep 2013 at 23:43.
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I know Boeing wouldn't design an aircraft that has solenoids energized with the battery switch off. Only the HBB would be energized and the miniscule clock draw the only drain. Six months after shutting down the aircraft the APU would start and you would be on your way.
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Originally Posted by Piper19
A non ER 757 main battery will give you 30 minutes of power (40amphours). On a ER version, you also have the HMG, which powers the hot batt bus for unlimited time, thus the battery will be charged all the time.
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Non ER battery will give you "approximately 30 minutes"(QRH) of power.
In the AA SEA-ORD event it lasted 97(?) minutes.
NTSB issues report on AA jet that lost battery power | Airline Biz Blog
In the AA SEA-ORD event it lasted 97(?) minutes.
NTSB issues report on AA jet that lost battery power | Airline Biz Blog
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I did a google search on Nicad battery drain and was surprised to see it is 20% per month so 5 months on a good battery. I deep cycled our Nicads in our Jetstar and replaced bad cells but thought they were more like lead acids on drain. Had one go into thermal runaway one day. Don't want to do that again.
bubbers44
NiCads are touchy beasts. What with their memory effect and flat voltage profile, verifying their state of charge and fully charged capacity is problematic. The only way to ensure a 'good' battery is to follow its maintenance and operations procedures carefully. Parking a plane (batteries installed) for months probably qualifies as being outside the envelope of normal operation. So the batteries would be suspect and not relied upon for capacity to support critical functions.
misd-agin
The 30 minute capacity is a minimum requirement. The systems design assumes some very conservative (worst case) electrical load profiles and a battery at the end of its uesful life. So its not unheard of to have the standby system remain operational for much longer. Just don't count on it.
NiCads are touchy beasts. What with their memory effect and flat voltage profile, verifying their state of charge and fully charged capacity is problematic. The only way to ensure a 'good' battery is to follow its maintenance and operations procedures carefully. Parking a plane (batteries installed) for months probably qualifies as being outside the envelope of normal operation. So the batteries would be suspect and not relied upon for capacity to support critical functions.
misd-agin
The 30 minute capacity is a minimum requirement. The systems design assumes some very conservative (worst case) electrical load profiles and a battery at the end of its uesful life. So its not unheard of to have the standby system remain operational for much longer. Just don't count on it.
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Yes, it is an old airplane but the 4 engine time helped me get an airline job. It counted more than a 4 yr college degree at Air California. Nothing was automatic. If you didn't flip a switch it didn't happen.
The cool part was unless a Gll was at your airport, you had the coolest corporate airplane there that you could walk down the isle without bending over. The APU made it a great place to take your girlfriend too. It was a slug performance wise but if you ever lost two engines it was your friend.
The cool part was unless a Gll was at your airport, you had the coolest corporate airplane there that you could walk down the isle without bending over. The APU made it a great place to take your girlfriend too. It was a slug performance wise but if you ever lost two engines it was your friend.
