Aircraft Batteries

[Bedawee_zeus]

Hello I am doing a degree in Aircraft Maintenance and at the same time the part 66 b1 license. I have come to the stage where I have to do a dissertation and boy did I pick a messed up one.

Title is: Whether or not it is viable to replace the conventional battery with PEM Fuel cells for aircraft emergency power.

I am taking it into consideration that the RAT is jammed or not working and the fuel has ran out on the aircraft and the APU is busted. So we are left with our tertiary line of emergency power the battery. The battery supplies power to vital and essential systems on the aircraft such as emergency light navigation equipment and so on.

Before coming here I have tried Airbus they're just rude and wont reply, so it is difficult for me to obtain accurate information.

So I need your help please based on your experience.

My question is how much current is being withdrawn from an aircraft battery during an emergency situation. I would like to specify on an aircraft such as Airbus a320. I know in general, emergency power lasts for around 30 minutes. The battery the a320 uses is 23AH (illustrated in the CMM, their may be different versions), I need to know the average current withdrawn during an emergency situation so I may compare this to a hydrogen fuel cell.

30 minutes nowadays is not acceptable so the amount of hydrogen stored will depend on how long it may supply power.

I thank you all in advance.

[ArthurR]

Bedawee_zeus, check your PM's

[mono]

You don't need us to tell you. You already have the answer. Certainly if you only need a rough guide.

Two 24V batteries each of 23 Ampere Hours and, in an emergency situation each feeding a separate buss (one AC and one DC. Not that this matters for the calculations). If the batteries are rated at 23AH and must last 30 minutes, then the average current draw on each buss will be???? Or do they not teach this simple stuff when they teach degree level engineering any more?

Anyway. Your fuel cell must supply 1.1 kilowatt to meet the above requirements for each buss. Then to be certified it must be rated at 1.5 times the requirement. So that means 1.6(ish) kW.

Therefore, if you intend to use a single fuel cell it must be 3.2 kW to supply emergency power for 30 minutes. As you have said in todays regulatory environment 30 minutes may no longer be sufficient.

You will also have to consider that if you remove the batteries. how are you going to start the APU from an unpowered airplane?

[ArthurR]

Mono, could use a cartridge start APU, If I remember rightly this was what the Vulcan had.

[Beeline]

New aircraft like the A380 are using electrical back up modules using the force of 5000psi hydraulic pressure still available from windmilling engines to power certain avionic systems and stand alone electro hydraulic actuators.

Due to the delivery pressure the components can still be quite small. Not sure on the output on these generators, quite small i guess but the technology is in place to be developed.

Regards B

[Krystal n chips]

" using electrical back up modules using the force of 5000psi hydraulic pressure still available from windmilling engines to power certain avionic systems and stand alone electro hydraulic actuators

Could you expand on this please because I am slightly confused as to how the hyd.systems are powering the avionics.....and how a windmilling engine can generate 5000 p.s.i.....and is this normal operating px for the A380 ?/

[Swedish Steve]

and how a windmilling engine can generate 5000 p.s.i.....and is this normal operating px for the A380 ?/
Windmilling engines turn engine mounted hydraulic pumps. This will produce full hyd pressure at very low RPMs. Watch an airliner starting its engines. As the first engine starts to rotate, you can see the ailerons move up to normal posn.
It needs some speed to get full hyd flow, but the FCOM will tell you what this is. You will usually have full hyds available on windmilling engines down to a landing, but then must be careful as you slow down as the pressure will dissapear.

[spannersatcx]

A330 AC EMERGENCY GENERATION
The AC emergency generation which consists of the Hydraulic Electrical Generating System (HEGS) enables to restore part of the distribution network in case of emergency configuration (loss of the two main busbars: AC 1 and AC 2).

The HEGS is composed of the following items:
- the hydraulic Constant Speed Motor (CSM),

- the AC generator,

- the Generator Control Unit (GCU).


The CSM and AC generator form an assembly called the Constant Speed Motor/Generator (CSM/G) 8XE.
In case of loss of the two main busbars AC 1 and AC 2, the CSM is supplied by the green hydraulic circuit which is powered:
- either by the green hydraulic engine driven pump(s) (one pump driven by engine and/or the other by engine 2) if one engine at least is operative,


- or by the Ram Air Turbine (RAT) pump in case of loss of both engines.

In case of loss of the AC main busbars, the CSM supplied by the hydraulic fluid drives the AC generator. The AC generator is controlled by the CSM/G GCU (1XE) and provides the AC power supply (115 VAC/400 Hz, 3 phases).
It supplies:
- the AC ESS buses (4XP, 9XP) through the EMER GLC (2XE),

- the DC ESS buses (4PP, 8PP) through the ESS TR.

The two main batteries supply the DC ESS BUS (4PP) and, via the static inverter, the AC ESS BUS (9XP) during the transfer to emergency generator operation after the loss of the main busbars.
The AC ESS SHED BUS (401XP) and the DC ESS SHED BUS (8PP) are shed respectively by the relay 16XH and the contactor 1PH when:
- the CSM/G is supplied by the RAT hydraulic pump and,

- in batteries only configuration.

So yes hydraulics can supply electrical AC power to power avionics bits and bobs.

[Beeline]

On the sauce but backed up by others. Thanks guys!

The orig post was using fuel cells as alternatives to batts. Why just have emergency batt when you can generate power from other means available to you.

Bit of a different angle available to the OPs dissertation if required.

Get yourself on a modern airliner course fargoo.

[Bedawee_zeus]

1st I'm really sorry for getting back to all of you and I am very grateful for your support. I thought that I would get an Email telling me that I got a response on my thread. Instead I was googleing away to find answers and I came across my own thread.

I was reading through and said this sounds like me, I look at the user and it was me haha.

I have found quite alot of information regarding what the battery supplies power to. These include communication, navigation (GPS or ILS) and also flight controls like the trim tabs on the rudder and elevator with electro mechanical actuators.

The average current of the battery is 70 amps which last for 30 minutes each and there are 2 on the a320.

Thank you again for your replies.

[Bedawee_zeus]

Thank you for your reply and Sorry for the late reply. I did get close enough readings to what you mentioned. I gave up on getting the accurate information for it was too time consuming and not relevent.

Thanks again :)

[Bedawee_zeus]

Hello Fargoo,
Thank you for your replies, you were very helpfull. Sorry for the late replies I thought I would get notified by email and I forgot all about it. I found my way here by googling. I read the message and it looked familliar and it was me. Silly of me!

I'm still here on earth, UFO's have not visited me yet.

Thanks Fargoo

Regards Zeus

[Bedawee_zeus]

It may have somthing to do with that this site is harder to get into than Fort Knox.

Yeah once this dissertation is over I'll sit down and figure everything there is to know about this site. Yeah I am more than half way now just need to work out how much hydrogen has to be stored on the aircraft to meet the time given in ETOPS. To be honest, it isn't viable as of yet for it's tooo big! There are like 5 subsystem, drag will be increased for this device needs air. I can't get bleed air for the engines are off.



Why don't they just shove a Tesla on it, or a magnetic generator. That would work however it is banned using those types of technology :rolleyes:

[md 600 driver]

it looks like 2 gazelle batterys
are the similar inside 20 cells ?

[Bedawee_zeus]

Thanks for the pictures. I managed to get that CMM from Saft. I was unable to get the maximum current wiithdrawal reading but I put it at 115 apms at 24 volts. Thats 2.8 KW with the safty factor included. This is with both batteries opperational at maximum load.

I got an email from Saft saying that the average current withdrawn from the 2 batteries are at 70 amps.

When there is a need to move the trim tabs for the ailerons, rudder and elevator they would consume more current.The trim tabs are electro hydraulically driven. Although it would not last long to deflect the trim tabs to the desired position, it would however depend on how good the pilot is and the weather conditions IMC. This is how I think they got to the average reading of 70 amps. Because the shunt of an extra 40, 50 , 60 amps would only last for like 2 or 3 seconds, till the trims are in possition and also when the aircraft is on it's correct flight path to the aerodome.

I hope that made sense :)

[ArthurR]

Zeus, check PM's