B737NG BAT DISCHARGE
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I refer the FCOM 2
" The hot battery bus is always connected to the battery. There is no switch in this circuit. The battery must be above minimum voltage to operate units supplied by this bus"
From my understanding, Mr Boeing wouldn't put this statement if it could be powered by another source.
" The hot battery bus is always connected to the battery. There is no switch in this circuit. The battery must be above minimum voltage to operate units supplied by this bus"
From my understanding, Mr Boeing wouldn't put this statement if it could be powered by another source.
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latetonite funnily enough this topic has already been spoken about.
I also reference Mr Chris Brady. 737 Electrics
Just to clarify I am talking about a scenario if BOTH the charger and Battery has failed.
I also reference Mr Chris Brady. 737 Electrics
Just to clarify I am talking about a scenario if BOTH the charger and Battery has failed.
As others have pointed out, BAT DISCHARGE means that the charger (or its supply) or the battery has failed. For the first two cases, the battery will now slowly discharge while supplying the hot battery bus and switched hot battery bus loads. Minus seven amps is not full standby load, indicating that AC and DC standby are still being powered by their primary sources. Given that discharge rate and a 36 Amp-hour battery, you will have approximately 5 hours until the battery reaches minimum voltage. If nothing else happens, you will be cutting into your standby capacity. That 30 minutes is what you have in the event all main power is lost and standby switches to the battery. Now that you are nibbling into that capacity, allowances may have to be made in the event an alternate airfield is needed.
Good move checking the battery current and bus voltages. But there is a limited amount you can diagnose beyond making sure things stay relatively stable. The reason for the charger failure could be of no consequence. Or it could be serious.
Good move checking the battery current and bus voltages. But there is a limited amount you can diagnose beyond making sure things stay relatively stable. The reason for the charger failure could be of no consequence. Or it could be serious.
Thread Starter
Thanks Eengnr, good info.
Latetonite you seem to be the only one posting here who hasn't understood the scenario we are talking about.( either that or we all misunderstand the system). I'll spell it out once more for clarity:
One hour into a three hour flight.
Single battery aircraft.
BAT DISCHARGE light illuminates.
That's it. That's the only indication you have that something is out of the ordinary with your aircraft.
In this circumstance something is amiss with the supply of power to the SHBB and the HBB and the battery has taken over supplying the power.
If the problem is not the No2 Transfer Bus then it is downstream of there and I don't see how you can be confident that the draw on the battery won't continue or increase as there is obviously a fault in the system.
When your battery gets low you are going to lose some critical systems from the SHBB and the HBB and you can't calculate with any certainty when that will be.
You seem to think that even though the battery is discharging, the TR units are supplying power to these two busses.
If this is true it is important information and we really need a source other than " your engineers will tell you". Where did you get that knowledge from?
I doubt it is true and think you may need to have an open mind towards changing your understanding of how the system works ( for reasons of flight safety).
Latetonite you seem to be the only one posting here who hasn't understood the scenario we are talking about.( either that or we all misunderstand the system). I'll spell it out once more for clarity:
One hour into a three hour flight.
Single battery aircraft.
BAT DISCHARGE light illuminates.
That's it. That's the only indication you have that something is out of the ordinary with your aircraft.
In this circumstance something is amiss with the supply of power to the SHBB and the HBB and the battery has taken over supplying the power.
If the problem is not the No2 Transfer Bus then it is downstream of there and I don't see how you can be confident that the draw on the battery won't continue or increase as there is obviously a fault in the system.
When your battery gets low you are going to lose some critical systems from the SHBB and the HBB and you can't calculate with any certainty when that will be.
You seem to think that even though the battery is discharging, the TR units are supplying power to these two busses.
latetonite Your engineers will tell you that current can flow from TR's to the DC busses to the switched and hot batt bus...
I doubt it is true and think you may need to have an open mind towards changing your understanding of how the system works ( for reasons of flight safety).
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Ok, if the battery fails, together with the batt charger, the hot battery busses are powered by the standby DC bus or stby power control, both fed by the dc busses, through the TR 's. this is clearly readable in the electric power diagram.
If the bus fails altogether, due to short, you have another ballgame.
If the bus fails altogether, due to short, you have another ballgame.
Last edited by latetonite; 7th Aug 2013 at 04:20.
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Ok, if the battery fails, together with the batt charger, the hot battery busses are powered by the standby DC bus or stby power control, both fed by the dc busses, through the TR 's. this is clearly readable in the electric power diagram.
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MULTIPLE FAILURES.
"I am presuming the 60 minutes endurance on the "fully charged battery" applies in the event of a further failure involving loss of generating ability, so we're looking at a double failure case." My post # 2.
I don't recall the OP mentioning further failures, which puts us in a whole new ballgame.
However, as the battery or batteries are there as a backup to loss of generator capability, then it's going to be an anxious time for all.
Maybe we won't get a hard and fast answer to the question, shame as the doubt has now been raised.
I don't recall the OP mentioning further failures, which puts us in a whole new ballgame.
However, as the battery or batteries are there as a backup to loss of generator capability, then it's going to be an anxious time for all.
Maybe we won't get a hard and fast answer to the question, shame as the doubt has now been raised.
I don't recall the OP mentioning further failures, which puts us in a whole new ballgame.
By the way, the post #25 diagram does not make the source switching for DC Standby and Battery Bus clear. Treat the arrows feeding the buses as diodes (although that may not be the actual implementation). Current does not flow through the battery bus from the TR unit to back feed the hot battery bus.
Thread Starter
Can we all agree that the primary source of power for the SHBB and the HBB in normal flight is the battery charger ( operating as a TR) and the secondary source of power for these two busses is the battery, and there is no third source?
If that's the case you don't have the ability to determine how long you have before losing your fire extinguishing capability in the described scenario.
If that's the case you don't have the ability to determine how long you have before losing your fire extinguishing capability in the described scenario.
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Sorry Framer, cannot agree. I wanted to upload an electrical diagram, more detailed than the one posted before, but have problems doing so. But there are available on the net.
Do not confuse a battery failure with a bus failure.
In your example, when the battery fails, plus the charger, the hot bat bus is fed via TR3. Then there is an auxiliary batt charger on the airplanes where there is a dual battery installed, also feeding the hot batt bus.
Yes, in case the hot battery and the switched batt bus would fail, you have another can of worms.
Do not confuse a battery failure with a bus failure.
In your example, when the battery fails, plus the charger, the hot bat bus is fed via TR3. Then there is an auxiliary batt charger on the airplanes where there is a dual battery installed, also feeding the hot batt bus.
Yes, in case the hot battery and the switched batt bus would fail, you have another can of worms.
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Latetonite :
We are NOT talking about a dual battery system. If the diagram is on the internet can you please give a link to it.
TR3 powers the battery bus but does not back feed through to SHBB and HBB like previous posters have said.
If you can show that it does then I shall walk with my tail between my legs.
We are NOT talking about a dual battery system. If the diagram is on the internet can you please give a link to it.
TR3 powers the battery bus but does not back feed through to SHBB and HBB like previous posters have said.
If you can show that it does then I shall walk with my tail between my legs.
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In your example, when the battery fails, plus the charger, the hot bat bus is fed via TR3
Thread Starter
By the way, the post #25 diagram does not make the source switching for DC Standby and Battery Bus clear. Treat the arrows feeding the buses as diodes
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You can only lead a horse to the water. You cannot make it drink.
The diagram in post nr. 29, not 25, is extremely simplyfied.
The link I provided to the B737MRG in readable by any 2nd year technical student.
For anybody to think to find simple flaws in studied and proven engineering, sounds just ridiculous.
Trust your commandership does not reflect the logical analysis exposed in this tread.
The diagram in post nr. 29, not 25, is extremely simplyfied.
The link I provided to the B737MRG in readable by any 2nd year technical student.
For anybody to think to find simple flaws in studied and proven engineering, sounds just ridiculous.
Trust your commandership does not reflect the logical analysis exposed in this tread.
Thread Starter
From the FCOM:
Normal operation.
So in normal operation the SHBB and the HBB are powered from the battery charger ( which in our scenario is faulty)
Then from the FCOM:
So in Alternate operation ( with the charger failed as per scenario) the SHBB and the HBB are powered from the battery. There is no mention of your mythical TR3 feed to the HBB as you say here
.
Normal operation.
Under normal conditions the AC standby bus is powered from AC transfer bus 1. The DC standby bus is powered by TR1, TR2, and TR3; the battery bus is powered by TR3; the hot battery bus and switched hot battery bus are powered by the battery/battery charger.
Then from the FCOM:
Alternate Operation
The alternate power source for standby power is the battery. With the standby power switch in the AUTO position, the loss of all engine or APU electrical power causes the battery to power the standby loads, both in the air and on the ground. The AC standby bus is powered from the battery via the static inverter. The DC standby bus, battery bus, hot battery bus, and switched hot battery bus are powered directly from the battery.
The alternate power source for standby power is the battery. With the standby power switch in the AUTO position, the loss of all engine or APU electrical power causes the battery to power the standby loads, both in the air and on the ground. The AC standby bus is powered from the battery via the static inverter. The DC standby bus, battery bus, hot battery bus, and switched hot battery bus are powered directly from the battery.
the hot bat bus is fed via TR3.