Flat Batteries
 

Scenario: Regional turbo-prop operation. Whoever left the aircraft last the night before left the battery switch ON. When the morning crew arrived .... Flat batteries !

Question. What happens to the battery in such circumstances. What are the consequenses of a battery flattened this way. Normaly the batteries are removed to be serviced in the maintenance shop ... but what is actually required to be done ? Do they just connect it to the charger and that's that or is there more to it ?

Question. If no maintenance facilities are available, can external power (GPU) be connected to the aircraft and let that recharge the battery in-situ ? If so are the batteries OK to continue or are they compromised in some way ?
Would appreciate some 'good info' on this. Can anyone help ?

If it goes wrong this could happen!

http://www.geocities.com/atalarczyk1/excel_batt

I don't know exactly what happened here but a picture paints a thousand words.

This is a double post, same asked in Tech Log, bad etiquet. Should be locked or merged.:=

T'was I who suggested that ooizcalling put this topic in the Eng Forum, from Tech Log. Bad etiquette:rolleyes: He's simply asking a question in two places!

Ni-cad batteries are often completelty flattened to avoid 'memory', where the battery will only charge to a certain voltage and not full capacity. The battery bay will charge them up again usually with no worries.

(I did wonder about having to bump start the aircraft with all the pax pushing the aircraft.....)

A nicad is normally made up of 19,20 or 21 individual cells. When it is competely flattened some cells will reach zero volts before others, and then go past zero to reverse polarity as the current continues to be drawn from the battery. Although some aircraft charging systems are becoming very sophisticated, they cannot normally account for the "reverse polarity" cells and continue to charge. These cells will then get hot, very hot, to the point where a thermal runaway could occur, and the battery could explode with devastating effect. (I've heard of the nose being blown off a Bell 206!).

Cells will vent during a charge and the battery shop will remove the vent caps to ensure no electrolyte spillage. They will control the current and check individual cell voltages and also check the electrolyte levels prior to returning the battery.

Basically, the battery shop will monitor every aspect of the charge and make sure you have a serviceable battery, not a bomb!:O

Every three months our batteries go into the shop (to prevent thermal run away etc) or when the crew leave the lights on or when the cabin crew cycle the pax door too many times which hopefully but not always results in flat battery before motor/clutch failure:ooh:
The problem is shipping batteries around from aircraft to workshops (our machines away from base a lot) as they are classified as hazardous goods

battery re charging.
 

A standard ni cad main battery is charged either by the aircraft system or removed to be charged in the Battery Shop.

The difference between the two processess is that on the aircraft the battery is charged at a constant voltage and varable current, while on charge after cap test the battery is charged at constant current, say 22 amps at a varable voltage.
Therefore the overheating caused by high current charging on the aircraft is avoided by the Battery Shop process.

regards om15

Hiya mate, happens regularly in our company....Basically your AOG for new batts.

Even if you could plug the aircraft in you couldn't charge mine in situ as they're not allowed on the bus when the voltage drops below a certain level..

:= :=

Still its an easy recovery and best of all the drivers solely to blame.:ok: :ok:

With any aircraft battery when the voltage drops below a certian level there is not enough current left to pull in the battery contactors so even if the GPU / APU can charge the batteries in situ you cannot get the batteries on line.

Those who apply an external voltage to the battery contactors to bring the batteries on line risk the scenario described by Brizeguy.

However sealed lead acid batteries are a bit more forgiving.

As per other posts a ni-cad nattery returned to the shop is completely discharged and each cell 'shorted out' so any cells that have reversed are corrected before any charge is applied.

The battery is then charged at the MM values and usually capacity checked by controlled discharge to ensure that no cells have failed and as long as the battery meets spec it is re-charged again and released for service.

Battery shop used to be a great place in the winter time!

Read the 757 AMM to see what you have to do if the battery is left on. Basically, although some company's prefer replacement, the AMM says a "flat" battery will charge within 75 minutes! Battery chargers generally work on constant current until 32v then reverts to constant voltage of around 28v
NiCad batteries in workshops monitored with sophisticated equipment to prevent polarity reversal.

Flat Batteries
 

A couple of points about batteries.
When a Ni-Cad battery is being charged it can have thermal run-away, even in fully controlled conditions in a battery charging bay. Results are pretty devastating and I would hate to see it occur on an aircraft.
The second issue is a flight safety one. Ask yourself why you have batteries on aircraft. They are there to run the necessary electrics when all else has failed. Certainly in the UK, there are requirements that an aircraft should be able to operate on emergency systems for 30 minutes on battery power alone.
I would suggest that if an aircraft is dispatched with a virtually flat battery, sooner or later someone is going to find out to their cost that a flat battery is not a good idea. Just imagine the scenario, flat battery, engines on, battery starts charging, taxy, take off, electrics fail, electrics shed to emergency bus-bar, battery runs down, oops!
To my mind that scenario gives only one option, replace flat battery with a fully charged one immediately.
P

Tread carefully
 

Bus429, that is the same for all widebody Boeings, they will constant current charge up to certain voltage then switch over to constant potential.
Using the aircraft to charge the batteries on the big girls might be OK, charging on the small stuff from flat using bus voltage - float charge -, not a good idea. There is a small chance that the line "Holy smoke Batman" might get used.

Good point
 

Split pin,
Sorry, yes, I should have made distinction that battery charging is a little more sophisticated on the big 'uns. Thanks for that.
I've been stuck in sticks on several occasions when, not having met the aircraft, I've opened a "dead" aircraft after 3 hours on the ground to be greeted by the ominous sound of the Stby Altimeter vibrator. In fact, this spawned a memorable thread on Jet Blast along the lines of "Why Can't Pilots Switch The Battery Off?". They invariably deny having forgotten to do so.

Regarding a flat battery, as mentioned earlier (for example) 757 charger will not start unless the voltage sensed at the output terminals is above 4 volts.

It is worthwhile checking with the manufacturer of the batt charger on your airplane what the low voltage protection is. This assumes that "flat" is not quite flat.............:confused:

I would have thought that A320/321 would be considered big 'uns?

They however use constant voltage to charge up their batteries with a BCL as a safety cutout. A fact that amazed me when I did the course as I thought they were supposed to be more advanced than their Boeing cousins.

Don't want to start another Boeing/Airbus debate just clarifying that's all