Just at the start

 

Note that the table you reference is for Voltage.  Yes, the bus will have the same voltage as the battery but NOT the same amperage.  Back to basics, you might have a hose and at the end there is a Y-connector and on the Y-connector there are two more hoses....with a low flow of water, there is an equal pressure in all three hoses but the flow in each is different.  Amperage is flow.  The BATT position switch measures the voltage for the battery and everything connected to it including busses that are connected, but it only measure current for the battery.  Hope that helps.

Jonathan you sound like a clever, clever chap but you lost me at "curved pressure variations". The sad thing is, I've yet to find a website that can explain these things in layman's terms. It has to be possible surely? So that science morons like me can understand?

 

By the way, like Vernon I'd be interested to know why switching the battery off in the 737 will turn off certain systems like the APU, caution panel, clocks, fire detection even though engine gens are working and operating normally. Is it like what Kevin said - that the very act of closing the battery switch isolates certain systems? Or does the battery actually power certain equipment in normal circumstances?

Change in pressure over change in time. Instead of a constant change it starts out steep and becomes very shallow when it peaks. Look at a sine wave graph and you will get the idea.

By the way, like Vernon I'd be interested to know why switching the battery off in the 737 will turn off certain systems like the APU, caution panel, clocks, fire detection even though engine gens are working and operating normally. Is it like what Kevin said - that the very act of closing the battery switch isolates certain systems? Or does the battery actually power certain equipment in normal circumstances?

 

It's a combination of both. Some systems, like the APU, use battery switch position for their logic. Others are powered by the switched hot battery bus, which loses power if the battery switch is off. Most DC powered items aren't affected by battery switch position if other power sources are available.

 

Clock power comes from the hot battery bus, which isn't switched, so should always be powered if the battery has voltage.

By the way, like Vernon I'd be interested to know why switching the battery off in the 737 will turn off certain systems like the APU, caution panel, clocks, fire detection even though engine gens are working and operating normally.

 

With normal power available turning off the battery switch removes power from the battery bus and the switched hot battery bus.  Anything powered by those buses will lose power.

So is the battery getting used during flight and getting charged by TR3?

The reason why the APU shuts down is because turning the bat off turns the fire protection off.

 

 

So is the battery getting used during flight and getting charged by TR3?

 

No.  The normal source of power for the battery bus is TR3.  The battery is kept charged by the battery charger.  When the battery is fully charged the battery charger acts as a TR and picks up the loads carried by the hot battery bus and the switched hot battery bus.

Yes BAT BUS is powered by TR3 through the SPCU or the K2 relay. And in normal conditions BAT BUS is isolated from the stand by system (K1 relay is OPEN)

 

So the HOT BAT BUS and SW HOT BAT BUS is getting power from where?

 

What do you mean acts as a TR?

 

 

So the HOT BAT BUS and SW HOT BAT BUS is getting power from where?

 

I already answered this, allow me to repeat myself, "When the battery is fully charged the battery charger acts as a TR and picks up the loads carried by the hot battery bus and the switched hot battery bus."

 

 

 

What do you mean acts as a TR?

 

Transformer rectifier, same as TR1, TR2 and TR3.

I already answered this, allow me to repeat myself, "When the battery is fully charged the battery charger acts as a TR and picks up the loads carried by the hot battery bus and the switched hot battery bus."

 

Sorry but i'm not very tech minded. You say picks up the loads from the hot bat bus and sw hot bat bus, will they not drain as there getting power taking from them for the bat?

That is interesting, and makes sense.  FCOM 6.20.13 confirms it.

 

Both battery and battery charger are connected to the hot bus loads, etc., but when the battery is fully charged the current will flow to the loads from the charger because it is designed to have a slightly higher voltage than the battery fully charged open terminal voltage.  This is required to work as a charger.  That's why it makes sense... it would be much more complex it it worked differently.

Q1. Is the BATT getting used during normal conditions?

 

In the absence of your definition of “normal conditions”, I’ll just consider it to mean “in-flight, in cruise configuration with no abnormal system conditions”. So, “in-flight, in cruise configuration with no abnormal system conditions” the answer is theoretically, no. There may be some small loads on the battery, but to no, or negligible consequence. The philosophy would be to preserve the energy in the battery for when it’s needed most. In other words, the battery is a backup DC source, if other DC sources aren’t available.

 

Q2. Why doesn't STBY PWR and BAT BUS never show DC AMPS?

 

These are not “power sources”, thus, current flow is not monitored. They form part of electrical distribution, not electrical generation. Only the Boeing System Engineer’s would be able to truly describe the philosophy here, but, your observation is correct – Current is not monitored for STBY PWR or BAT BUS for display on the AC/DC Metering Panel.

 

The HOT BAT BUS is the BAT on the DC PANEL

 

This assertion needs to be re-considered for completeness. Refer Joe Diamond’s post – post #37… “The normal source of power for the battery bus is TR3”. Your statement is only correct when - TR3 is not powering the Battery Bus – in which case, current flow is displayed for the “power source” (the Battery, or Batteries), and not the distribution Bus.

 

Q4. Does the main battery get charged during flight?

 

Only if it drops to below a pre-defined voltage. Once it’s recharged, the battery is left alone, assuming no abnormal conditions.

 

Q5. Is the battery getting used during flight and getting charged by TR3?

 

No, it is not used during flight. It gets charged by the Battery Charger/Chargers. This doesn’t mean you can switch the Battery Switch off during flight! Logic is key here, much too complex to understand or explain without drawing direct reference to the Maintenance Manuals, not normally available to the public.

 

Q6. So the HOT BAT BUS and SW HOT BAT BUS is getting power from where?

 

Refer to Joe Diamond’s post – post #39. They get it from the Battery Charger/Chargers; assuming the battery is not the only power source, or the battery is in the process of getting charged.

 

Why are you digging such a deep hole, out of curiosity?

 

Brian Nellis.

Right so the chargers are getting the power from the AC GND SERVICE BUSES which then supply the HOT BAT BUS and SW HOT BAT BUS is that correct?

Correct.

 

Brian Nellis.

Q1. Is the BATT getting used during normal conditions?

 

In the absence of your definition of “normal conditions”, I’ll just consider it to mean “in-flight, in cruise configuration with no abnormal system conditions”. So, “in-flight, in cruise configuration with no abnormal system conditions” the answer is theoretically, no. There may be <snip>

 

Brian Nellis.

Well explained Brian. I was about to pick up the water analogy again and then luckily decided to read the thread to it's preliminary (?) end. At the beginning I was asking myself if we would end up with Maxwell's equations. :huh: