- hmm! Tell that to my squadron's 'Intelligence Officer' whose VW Golf's clock flattened his battery in 10 days...................Still, I think we can safely assume the 757's battery will last at least for full tanks.:)

I drive our second car once every 3 months and it starts. The clock is always running.

Main Battery Charger
 

It said Main Battery Charger

disguising myself?
 

How am I doing that?

I am a copilot on the 757 for American.

I was one of those flow through eagle pukes 3 years ago.

Does that help?


:ugh:

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).

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.

NiCad self discharge might be an issue that far out. The APU might start if it lights up on the first try.

- getting slightly off topic here? The figures you quote refer to a main generation failure situation, not a battery charger failure, in which we have established the busses will be powered normally, and also the HMG cannot 'maintain' battery charge, but merely reduce the drain.

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

A bit thin on information there, misd - what was/were the fault/s?

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.

Jetstar...there's something I haven't seen in a while, except in pictures.

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.

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.