737 Electrics Part 2 - DC Power

[@rossinisilva1302]

This content is mined gold on the vast BS found on YT. Student maintenance engineer here using your videos and website for general knowledge of aircraft systems. Thank you Mr. Brady

[@ChrisBrady737]

Thank you for your kind comments. I am glad you are finding my work useful.

[@RedEye737]

Captain, as someone truly wants to elevate his knowledge about this majestic airframe, you are the definitive source of invaluable information. I've been flight simming for a long time now. Although, only over the last year have I had the privilege of acquiring PMDG 737, which simulates electrical systems real-time . I only can dream I had the funds to become a real 737 driver, but for now, this unquestionably brings me closer to understanding this bird. All the best to you

[@ChrisBrady737]

My pleasure. I am happy to hear that my videos are helping you to get more out of your hobby.

[@MrRicardovicentin]

Thanks!

[@ChrisBrady737]

You are very welcome

[@BellaItalia368]

Thanks

[@ChrisBrady737]

Thank you, much appreciated 🙏

[@HAWK21M]

Long videos… but very much in detail…. Thanks Chris. Im curious to know why amber cb collars are used…..trying to get the answer at work.

[@ChrisBrady737]

Hi Meljoe, the colour coding of c/b collars is not standardised. So the colours may have different meanings in different airlines.

[@neekoweeclearwater2305]

Great breakdown of the DC power system!

[@ChrisBrady737]

Thank you and thanks for watching

[@panagiotissoutsas7851]

Captain you have to do a video with the elec failures! would be amazing! Great Job

[@ChrisBrady737]

I generally try and restrict my work (videos, website & book) to technical details rather than get into operational procedures as these may vary with different operators, but I will see what I can do.

[@barendalberts460]

Thanks for sharing. Great content.

[@ChrisBrady737]

You are welcome, thanks for watching

[@ncooper8438]

In light of the Jeju 737 crash, maybe CB could give a short update on what Automatic reconfiguration of the electrical system would have occured after the loss of both ac generators, and whether any manual reconfiguration would have been necessary to make use of the DC and Standby busses.

[@tomstravels520]

He has done a recent video about recorder power which does go into some detail about standby power but essentially it's just the batteries power the AC and DC standby systems

[@ncooper8438]

Thanks, I've watched it, CB is good but in this case he says little about automatic switching and reconfig, or pilot actions if all AC lost. That's why I posted.

[@ChrisBrady737]

The standby busses are automatically powered after the loss of all AC power.

[@mandeepkulhria720]

Videos are very informative and helpful ..thanks for sharing 🙂

[@ChrisBrady737]

My pleasure 😊

[@elmin2323]

Question i thought of the other day while we had 1 eng gen on mel. What would happen if the main bat charger fails (on a single battery 737 ng) once airborne? Would the switched battery bus all and hot Battery bus fail after 30 odd minutes? What would the indications be? Elec light only comes one on thr ground.

[@ChrisBrady737]

Please ask any operational or technical questions here: facebook.com/groups/737tech

[@someonesomewhere1240]

Battery life should be significantly longer than 30 minutes as you are not supplying the standby or battery buses from the battery, only the hot/switched hot battery buses. Most loads on those buses are either very low (e.g. clocks powered even while aircraft is off) or only draw power when relevant, such as warning lights, fire indicators, valve controls etc. Looks like biggest loads are probably ADIRU DC supplies (not sure if these draw any current while they have AC supply) and APU and generator controls (hopefully these are self-powered when operating, or a shorted battery would be a pretty bad single point of failure). If you are drawing more than 5A on those buses (I expect this is unlikely?) you'll get a battery discharge light after a few minutes and you'll probably still have several hours battery. If you're drawing less than 5A, a hypothetical 36Ah single-battery NG ought to last at least 7 hours. A total generator failure after discharging the batteries would not be good, but is very edge case. Obviously this is not formal advices...

[@victorsokolov]

what a great content, thank you so much!

[@ChrisBrady737]

You're very welcome, glad you enjoyed it.

[@T0MaTOS]

THANK YOU, CHRIS!

[@ChrisBrady737]

My pleasure

[@MatthijsvanDuin]

41:55 Out of curiosity, why did those breakers need to be pulled during this airworthiness check flight? Was it just to avoid nuisance warnings?

[@ChrisBrady737]

The CBs were not pulled together but one at a time, so the tests could be conducted on each system individually.

[@nassoi]

thank you for great presantation

[@ChrisBrady737]

You are most welcome

[@abeldpl]

Hi, i might have missed the explanation, if i did i apologize, but could you explain the role of the diode between TR3 and TR2? I cannot find any answer in my company books. Thanks for the content

[@ChrisBrady737]

A diode only allows electricity to flow in one direction, think of them like one way vales. The diode between TR3 & 2 shows that TR3 is backing up TR2 and not the other way around.

[@sebastianmatiasanzoategui4248]

Great videos.

[@ChrisBrady737]

Thank you!

[@DL14204]

In a dual engine failure (Sully scenario) no APU powered only DC, is the Standby Hyd System available?

[@ChrisBrady737]

The standby hyd pump is electrically powered from AC Transfer bus 2. So, if that remains powered, you will have standby hydraulics. In your (unlikely) scenario of no engines and no APU then you will have no AC source to power the AC transfer busses, so no standby hydraulics.

[@huggksn4787]

Appriciated 🎉

[@ChrisBrady737]

You are welcome

[@gatorbuc99]

Good day Chris, With regards to the Standby Power guarded switch, I wonder why Boeing included a ‘Bat’ position...isn’t it completely in line with the functions of the ‘Auto’ position?

[@ChrisBrady737]

The BAT and AUTO positions have different air-ground logic and different sources to power the standby busses.

[@gatorbuc99]

@@ChrisBrady737 Ahh, I see. Thank you. Great channel, sir!

[@rishabhchhabra777]

Superb. Your e-book link doesn’t have the option to download it. Says book link removed.

[@ChrisBrady737]

@rishabhchhabra777 On your iPhone or iPad open the Books App. Search for "737 Technical". You may see two versions of the eBook, you want the one which has a release date of 2022 3 February. Enjoy!

[@rishabhchhabra777]

@@ChrisBrady737 says not available in the store for your country or region. (India)

[@ChrisBrady737]

Ah sorry, unfortunately I can’t help if Apple Books do not sell to your region, that is out of my control. Apologies.

[@rishabhchhabra777]

@@ChrisBrady737 no worries, videos are equally helpful. Thanks again for the good work!

[@Driver170]

Hi, great channel. Got a question on the DC system. If you loose Transfer bus 1 or a power source to DC Bus 1 why doesn’t transfer bus 2 not pick this up? But the batt and aux batt chargers do

[@ChrisBrady737]

The DC cross bus tie relay will power the DC busses if Transfer Bus 1 is unpowered

[@Driver170]

@@ChrisBrady737 Hi, from the FCOM With loss of AC transfer bus 1 or the source of power to DC bus 1, the AC and DC standby busses are powered by the main and auxiliary battery/battery chargers.

[@ChrisBrady737]

I think we are not quite understanding each others questions and responses - always a danger with short written Q&A! If transfer bus 1 is lost, DC Bus 1 will be powered by Transfer Bus 2 via TR2&3 through the cross bus tie relay. So transfer bus 2 does "pick this up" Does this answer your question?

[@Driver170]

@@ChrisBrady737 Full understanding is vital. Thats how i understood until i read that part in the FCOM i quoted above though?

[@Driver170]

@@ChrisBrady737 So what about the AC and DC standby buses?

[@jayvete6665]

Awesome Sir

[@ChrisBrady737]

Thank you

[@manwickwilson7392]

Nice 🎉

[@ChrisBrady737]

You are welcome

[@СкуратовЯрослав-ю1я]

Like!

[@ChrisBrady737]

Thanks!

[@marcelhorstmann6435]

Thanks!

[@ChrisBrady737]

Thank you very much for your generosity 🙏