737 NGX Electrics help

[Driver170 42]

Hi, i'm currently studying the Electrics side of the NGX and needing some usefull articles to explain this mind numbing subject.

 

I know AC is alternating current and DC is direct, goes one way. I've read it all up on google. Thats the very basic level i know. So i'm looking for a good site where this is explained in more detail about the currents on aircrafts electrics. I also need help on the AC DC METERING PANEL on the overhead panel. You have the AMPS reading AC AMPS and DC AMPS, what does the AMPS do for the electrics?

 

Also you have CPS FREQ which is about 400 yet again i only know this means cycles per minute!

 

So if anyone can brake this subject down for me to understand it will be great or even post some good links to sites explaining all this.

Also why doesn't STBY PWR and BAT BUS never show DC AMPS?

 

And does the NGX simulate the Ground Power Relay or the switch?

[jaguara5 1]

Watch in youtube  "cbt 737 electrical system"

Gerasimos Stamatatos

[Driver170 42]

I understand the schematics and what powers what etc its just understanding what AC and DC AMPS are? I know there both the same.

[kevinh 409]

Google Ohms Law. You need a basic grasp of what voltage and current are to understand any electrical system.

[Driver170 42]

Its not an easy thing :(

[Driver170 42]

Ok done some reading! But still can't see why STBY PWR and BAT BUS never show DC AMPS and also the INV?

[rondon9898 84]

Are you trying it when all electrical systems are working normally? Because I'm pretty sure the STBY power and inverter won't be energised unless there's a complete AC system failure, which would explain why the amperage isn't shown.

[downscc 1,327]

Its not an easy thing :(

Actually, very easy.  Popular analogy is to stream of water.  The flow gal/sec is analogous to Amperage (we capitalize because Ampere was a man), pressure lbs/sq-in is Volts (Voltaire another man) and resistance a little harder but imagine a plate with a hole in it in the pipe only allowing the flow to pass through the small hole (orifice plate), this is resistance measured in Ohms (a very great man).  They are all related in electricity (unlike actual fluid dynamics) where 1Amp x 1Ohm = 1Volt.  Keep volts constant and increase amps, you must reduce ohms which is exactly what happens when you add a "load"  Each additional  load represents an increase in pipe size or orifice hole for a reduction in resistance to allow more current (water or Amps) at a given Voltage.  It is up to the provider of all this water (the generator) to keep providing enough pressure or Voltage as the load increases.

 

The defined unit is the Ampere from which all else is derived and is one Coulomb/second where Coulomb (another man) is a certain number of positive charge carriers but most electricians are comfortable with the idea of electrons being the charge carriers and it works either way (just watch your signs).

 

See, not complicated. Like water flowing in a pipe.

[PMDG777 231]

Actually, very easy. Popular analogy is to stream of water. The flow gal/sec is analogous to Amperage (we capitalize because Ampere was a man), pressure lbs/sq-in is Volts (Voltaire another man) and resistance a little harder but imagine a plate with a hole in it in the pipe only allowing the flow to pass through the small hole (orifice plate), this is resistance measured in Ohms (a very great man). They are all related in electricity (unlike actual fluid dynamics) where 1Amp x 1Ohm = 1Volt. Keep volts constant and increase amps, you must reduce ohms which is exactly what happens when you add a "load" Each additional load represents an increase in pipe size or orifice hole for a reduction in resistance to allow more current (water or Amps) at a given Voltage. It is up to the provider of all this water (the generator) to keep providing enough pressure or Voltage as the load increases.

 

The defined unit is the Ampere from which all else is derived and is one Coulomb/second where Coulomb (another man) is a certain number of positive charge carriers but most electricians are comfortable with the idea of electrons being the charge carriers and it works either way (just watch your signs).

 

See, not complicated. Like water flowing in a pipe.

In all my life studying physics and engineering I have never heard it being described like that. It's perfect!

[Driver170 42]

Are you trying it when all electrical systems are working normally? Because I'm pretty sure the STBY power and inverter won't be energised unless there's a complete AC system failure, which would explain why the amperage isn't shown.

 

I done some digging and STBY PWR plus BAT BUS will never show amps because its not a source of power?

Actually, very easy.  Popular analogy is to stream of water.  The flow gal/sec is analogous to Amperage (we capitalize because Ampere was a man), pressure lbs/sq-in is Volts (Voltaire another man) and resistance a little harder but imagine a plate with a hole in it in the pipe only allowing the flow to pass through the small hole (orifice plate), this is resistance measured in Ohms (a very great man).  They are all related in electricity (unlike actual fluid dynamics) where 1Amp x 1Ohm = 1Volt.  Keep volts constant and increase amps, you must reduce ohms which is exactly what happens when you add a "load"  Each additional  load represents an increase in pipe size or orifice hole for a reduction in resistance to allow more current (water or Amps) at a given Voltage.  It is up to the provider of all this water (the generator) to keep providing enough pressure or Voltage as the load increases.

 

The defined unit is the Ampere from which all else is derived and is one Coulomb/second where Coulomb (another man) is a certain number of positive charge carriers but most electricians are comfortable with the idea of electrons being the charge carriers and it works either way (just watch your signs).

 

See, not complicated. Like water flowing in a pipe.

 

Fantastic! I think you should stick around you know your stuff

[rondon9898 84]

Dan when you say voltage is analogous to water pressure, could you possibly explain that a bit? I've had lots of very clever people explain the fundaments of electricity to me and they've always come up with the water analogy, but I've never quite understood it. Current and resistance I can completely understand, but even as a teenager doing school physics I never understood what exactly voltage was measuring. A bit embarrassing being an adult male and not knowing that really. Will no doubt come in useful when I start going into professional flying ^_^ .

[downscc 1,327]

 

 

I done some digging and STBY PWR plus BAT BUS will never show amps because its not a source of power?

 

You are close enough, yes. We haven't talked about power... different from Volts and Amps.  Amps are zero because current is not flowing.

[Driver170 42]

You are close enough, yes. We haven't talked about power... different from Volts and Amps.  Amps are zero because current is not flowing.

 

I only mentioned this in my post and wasn't sure why it never shows a reading. It doesn't even have a 0 for the amps. It doesn't read amps full stop as i've found out but don't know why?

 

Could you tell me, is the BATT getting used during normal conditions? Because if it is why doesn't it run out then? I know during non normal conditions its used to supply the STBY PWR system.

[downscc 1,327]

 

 

what exactly voltage was measuring

 

Yeah, the water analogy will break down when you look close.  But your faucet has water pressure behind it and that can be taken to be analogous to voltage.  Take a common 9V battery, like in your smoke detector. What does 9V mean?  There' no current or power, the battery is just setting there not doing anything but it has 9 volts of what?  If you could see electromagnetic fields (other than light which we can see) then you would see that an electric field existed between the terminals on the battery.  You are more familiar with magnetic fields, you can visualize this with iron flakes on a piece of paper with a magnet held below and see 'lines' of the field and a compass aligns itself with the earths' magnetic field.  Okay, well a magnetic field is part of the electromagnetic field.... it's there.  And it will do work when you connect something to the battery terminals, the field will act on the electrons and 'force' them to flow causing a current.  The greater the force the more the flow and the greater the force the higher the voltage.  Hope that helps.

I only mentioned this in my post and wasn't sure why it never shows a reading. It doesn't even have a 0 for the amps. It doesn't read amps full stop as i've found out but don't know why?

Could you tell me, is the BATT getting used during normal conditions? Because if it is why doesn't it run out then? I know during non normal conditions its used to supply the STBY PWR system.

The BATT will show current when it is the only source of power, no engines or APU running and no ground connections and battery is on.. it will also show a little current when it is being charged, but normal battery current flow is very small and not readable on that gauge.

[Driver170 42]

The BATT will show current when it is the only source of power, no engines or APU running and no ground connections and battery is on.. it will also show a little current when it is being charged, but normal battery current flow is very small and not readable on that gauge.

 

Yes thats right BAT on the OH shows DC AMPS 0 and DC VOLTS 28 but my question is why doesn't BAT BUS and STBY PWR not show DC AMPS?

Does the main battery get charged during flight?