B737NG BAT DISCHARGE
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At the end of the day latetonite , either you are wrong or I am wrong. It is important to understand this system so I am open to the possibility that I am wrong and am ready to change my mindset. At this point in time however you have only provided analysis of the Boeing docs that is contradictory to mine and several other posters here, one of whom appears to be an Electrical Engineer.
I am going to pursue this with my own companies Engineers to get a definitive answer. If you are open to changing your mindset on how the system works I will come back on here with the outcome, if you are going to doggedly stick to your own personal analysis of the schematic ( which is at odds with everyone else on here) I will not continue discussing it here as it is pointless and puts mis information on the thread that may confuse new pilots trying to learn.
If the Engineers conclude that you are right I will post that here.
I am going to pursue this with my own companies Engineers to get a definitive answer. If you are open to changing your mindset on how the system works I will come back on here with the outcome, if you are going to doggedly stick to your own personal analysis of the schematic ( which is at odds with everyone else on here) I will not continue discussing it here as it is pointless and puts mis information on the thread that may confuse new pilots trying to learn.
If the Engineers conclude that you are right I will post that here.
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Framer,
I asked you to pm me an email address, where I can send you the wiring diagram AND the reference to my mythical TR3. I cannot post it on the tread.
And yes, if it helps, my background is electrical, electronical engineering with military specialisation in avionics.
But check with your engineers.
I asked you to pm me an email address, where I can send you the wiring diagram AND the reference to my mythical TR3. I cannot post it on the tread.
And yes, if it helps, my background is electrical, electronical engineering with military specialisation in avionics.
But check with your engineers.
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Framer,
You are correct. The HBB and SHBB are powered from the battery or charger. TRU 3 does not supply either, in any configuration.
MyBoeingFleet's simplified electrical schematic, and WDM 28 VDC buses schematic clearly show this.
I am not claiming to be an expert on all things maintenance, but I have held a B737NG AMEL type rating for over 10 years, including the Electrical category.
lateonlite,
Perhaps you are looking at the K3 standby DC alternate relay and thinking that TR3 can supply DC power through it to the Hot battery buses in the event of a battery/charger failure??
The K3 relay is relaxed open. It energises closed to allow the battery or the charger to power the DC standby busses. This happens when the standby power switch is in AUTO and either or both DC bus 1 and AC transfer bus 1 have no power. The K3 relay will not be energized by a battery and/or charger failure, and therefore TR3 cannot power the hot battery busses. The SPCU controls all this.
The only source of power to the hot battery buses is the charger or the battery. If both fail you have lost the hot busses. The AUX battery was installed to prolong emergency power as well as provide a third source of power to these buses. This provides 3 levels of redundancy to the hot battery busses.
You are correct. The HBB and SHBB are powered from the battery or charger. TRU 3 does not supply either, in any configuration.
MyBoeingFleet's simplified electrical schematic, and WDM 28 VDC buses schematic clearly show this.
I am not claiming to be an expert on all things maintenance, but I have held a B737NG AMEL type rating for over 10 years, including the Electrical category.
lateonlite,
Perhaps you are looking at the K3 standby DC alternate relay and thinking that TR3 can supply DC power through it to the Hot battery buses in the event of a battery/charger failure??
The K3 relay is relaxed open. It energises closed to allow the battery or the charger to power the DC standby busses. This happens when the standby power switch is in AUTO and either or both DC bus 1 and AC transfer bus 1 have no power. The K3 relay will not be energized by a battery and/or charger failure, and therefore TR3 cannot power the hot battery busses. The SPCU controls all this.
The only source of power to the hot battery buses is the charger or the battery. If both fail you have lost the hot busses. The AUX battery was installed to prolong emergency power as well as provide a third source of power to these buses. This provides 3 levels of redundancy to the hot battery busses.
Last edited by Gas Bags; 9th Aug 2013 at 02:12.
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GB,
I am not referring to K3, as this one, correctly, closes when either DC bus 1, or/and AC transfer bus 1 has no power, i.e. generators not available.
In normal flight however, with the battery switch on, stby pwr not in bat position, K2 is closed and connects TR3 to the bat bus via SPCU.
TR3 is normally powered by Transfer bus 2, alternatively by Transfer bus 1.
If TR 3 fails, or has no power, K1 closes, to energise the battery bus from the battery or the battery charger.
The battery bus, and the switched hot batt bus via the batt switch, are now energized, so fire detection and extinguishing is available.
This was the main issue in the loss of battery and batt charger, as I understand.
I am not referring to K3, as this one, correctly, closes when either DC bus 1, or/and AC transfer bus 1 has no power, i.e. generators not available.
In normal flight however, with the battery switch on, stby pwr not in bat position, K2 is closed and connects TR3 to the bat bus via SPCU.
TR3 is normally powered by Transfer bus 2, alternatively by Transfer bus 1.
If TR 3 fails, or has no power, K1 closes, to energise the battery bus from the battery or the battery charger.
The battery bus, and the switched hot batt bus via the batt switch, are now energized, so fire detection and extinguishing is available.
This was the main issue in the loss of battery and batt charger, as I understand.
Last edited by latetonite; 9th Aug 2013 at 03:39.
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latetonite,
To be honest I'm not even sure what point you are arguing any more
Why are you talking about the bat and dc standby buses? You said:
Hence we were talking about TR3 feeding the hot buses. Look at FCOM2 6.2.18.
But all this is by the by. The scenario is normal AC power with the BATTERY DISCHARGE light illuminated. If that light is on, the battery is being drained and therefore what you do know for sure is that anything connected to the battery is threatened.
To be honest I'm not even sure what point you are arguing any more
Looking at your FCOM 6.20.3, TR3 does feed the DC stby bus, no?
And in FCOM 6.20.15, DC power distribution, it is clear that TR3 feeds the battery bus via stby pwr PCU.
when the battery fails, plus the charger, the hot bat bus is fed via TR3.
But all this is by the by. The scenario is normal AC power with the BATTERY DISCHARGE light illuminated. If that light is on, the battery is being drained and therefore what you do know for sure is that anything connected to the battery is threatened.
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Framer,
You are still correct.
lateonlite,
You have essentially repeated my post and I agree with everything you state.
Can you cover off on exactly how TR3 can power the hot battery busses??? I don't need a circuit diagram or any reference, just the relay/switch numbers and what circumstances cause them to allow TR3 to power the hot battery buses??.....As Framer has said this will clarify for youngsters out there willing to learn.
You are still correct.
lateonlite,
You have essentially repeated my post and I agree with everything you state.
Can you cover off on exactly how TR3 can power the hot battery busses??? I don't need a circuit diagram or any reference, just the relay/switch numbers and what circumstances cause them to allow TR3 to power the hot battery buses??.....As Framer has said this will clarify for youngsters out there willing to learn.
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GB: answer to your inquiry is in my post #44. For your conveniance I paste it again:
In normal flight however, with the battery switch on, stby pwr not in bat position, K2 is closed and connects TR3 to the bat bus via SPCU.
K2 is the normal batt bus relay switch.
I have trouble understanding what makes this so difficult to comprehend.
In normal flight however, with the battery switch on, stby pwr not in bat position, K2 is closed and connects TR3 to the bat bus via SPCU.
K2 is the normal batt bus relay switch.
I have trouble understanding what makes this so difficult to comprehend.
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To make you more upset, the battery discharge light will not illuminate when AC transfer bus #1 is powered. So basicly only on the ground with no engine running and no external power.
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Funny - I always assumed that the triangles in the electrical circuits in the diagrams represented diodes. According to 'late' they do not?
Hey look! EEng who claims to be an ex Boeing engineer agrees
Hey look! EEng who claims to be an ex Boeing engineer agrees
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
There is no link in post 44.
Latetonite, does it make you uncomfortable that so many other people disagree with your interpretation of the system?
I asked my companies Engineers and they agree that the HBB and SHBB are fed by the battery charger as a primary source and by the battery as a back up. There is no third source.
Latetonite, does it make you uncomfortable that so many other people disagree with your interpretation of the system?
I asked my companies Engineers and they agree that the HBB and SHBB are fed by the battery charger as a primary source and by the battery as a back up. There is no third source.
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ltn means post #34 and now has the difficult task of explaining how the 'correctly fitted diode' would allow current flow in both directions.....................................
Do we have 'son of SSG' here?
Do we have 'son of SSG' here?
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He certainly has no understanding of circuit diagrams or basic electrical theory, and has an obvious inability to admit he is wrong.
Tipping the 'ol wrist a bit, me suspects.
Tipping the 'ol wrist a bit, me suspects.
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Dear latetonight
You said during normal ops the K2 relay is closed and TR3 powers the Battery Bus. And you say the HBB & SHBB will be powered by TR3 once the battery goes flat and the charger is not working.
The only way I can see that (using the diagram given by you) is if the K1 relay (between the Battery Bus and the Battery) closes and the current somehow jumps a one-way diode which is pointing UP which says current can only flow form the Battery to the Battery Bus and not reverse.
So I would like to understand how is it possible for K2 and K1 relays to be closed both together and if that were to occur how would the current bypass the diode??
Also I find you the rudest here and you the one asking someone to be polite. Sorry but that’s just hilarious.
You said during normal ops the K2 relay is closed and TR3 powers the Battery Bus. And you say the HBB & SHBB will be powered by TR3 once the battery goes flat and the charger is not working.
The only way I can see that (using the diagram given by you) is if the K1 relay (between the Battery Bus and the Battery) closes and the current somehow jumps a one-way diode which is pointing UP which says current can only flow form the Battery to the Battery Bus and not reverse.
So I would like to understand how is it possible for K2 and K1 relays to be closed both together and if that were to occur how would the current bypass the diode??
Also I find you the rudest here and you the one asking someone to be polite. Sorry but that’s just hilarious.
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Dear Framer:
I had this a week back just after takeoff. With -5 amps on the Metering panel. I called maintrol and they told me that my battery would go flat in 1 hour. My flight was over 2 hours long. Thus did an ATB.
After landing I was told that -5 wouldn’t have drained the battery and that if I had chosen to continue I could have as the battery wouldn’t have drained that fast as it wasn’t a huge value. But they did say that if the battery did drain out the HBB and SHBB would be unpowered. I shall put up a PDF file which shows the equipment that are powered by the HBB and SHBB.
While on the R/T I got wrong info from maintrol that my Battery would drain out in 60 mins, as -5 amps would have taken it much longer to drain. Nonetheless safety are happy that I came back as I was headed to Delhi where it was CAT 3 conditions so no tea or biscuits with management as of now. Though once I have the official report I shall publish it here.
I though have one last thing to add. The FCOM says
With the BAT Switch in OFF –
• removes power from battery bus and switched hot battery bus when operating with normal power sources available
• removes power from battery bus, switched hot battery bus, DC standby bus, static inverter, and AC standby bus when battery is only power source.
So now to me that means regardless of normal power or not if the BAT is OFF the battery bus will also not be powered along with the SHBB and HBB.
Thus on the same lines once the Battery is flat and the charger not working would the battery bus be powered even though we have normal AC power???
As per me once the Battery goes flat and the charger not working the SHBB, HBB and the Battery Bus also would be unpowered.
What do you think?
I had this a week back just after takeoff. With -5 amps on the Metering panel. I called maintrol and they told me that my battery would go flat in 1 hour. My flight was over 2 hours long. Thus did an ATB.
After landing I was told that -5 wouldn’t have drained the battery and that if I had chosen to continue I could have as the battery wouldn’t have drained that fast as it wasn’t a huge value. But they did say that if the battery did drain out the HBB and SHBB would be unpowered. I shall put up a PDF file which shows the equipment that are powered by the HBB and SHBB.
While on the R/T I got wrong info from maintrol that my Battery would drain out in 60 mins, as -5 amps would have taken it much longer to drain. Nonetheless safety are happy that I came back as I was headed to Delhi where it was CAT 3 conditions so no tea or biscuits with management as of now. Though once I have the official report I shall publish it here.
I though have one last thing to add. The FCOM says
With the BAT Switch in OFF –
• removes power from battery bus and switched hot battery bus when operating with normal power sources available
• removes power from battery bus, switched hot battery bus, DC standby bus, static inverter, and AC standby bus when battery is only power source.
So now to me that means regardless of normal power or not if the BAT is OFF the battery bus will also not be powered along with the SHBB and HBB.
Thus on the same lines once the Battery is flat and the charger not working would the battery bus be powered even though we have normal AC power???
As per me once the Battery goes flat and the charger not working the SHBB, HBB and the Battery Bus also would be unpowered.
What do you think?
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Dear Sirani,
Many of my ab initio students think I am rude. As a matter of fact, quite a few of the captains I train think so.
But most of them admire me after being on line for a while.
And yes, they would not RTB like you mentioned in your experience.
But that is me, after 36 years of airline flying.
Nowadays, it seems to be a different way of doing things.
That does not mean I trust the new breed of so called paper captains.
Please do not take this as an offence. After all, your assertiviness did bot offend me either.
Many of my ab initio students think I am rude. As a matter of fact, quite a few of the captains I train think so.
But most of them admire me after being on line for a while.
And yes, they would not RTB like you mentioned in your experience.
But that is me, after 36 years of airline flying.
Nowadays, it seems to be a different way of doing things.
That does not mean I trust the new breed of so called paper captains.
Please do not take this as an offence. After all, your assertiviness did bot offend me either.