Battery discharge warning right or wrong?

[davidlondon 0]

Expectations are deservedly sky-high with NGX, so I am dutifully stepping through Tom Risager's excellent tutorial checklist. Came to the bit about the battery discharge light and also checked in the operating manual: essentially "excessive" battery discharge will bring on the amber warning light. So I tried a ground experiment:

1. Ground power on and selected
2. Landing lights and other electrical services on
3. Switched off ground power and observed increased battery drain on the DC meter - but no discharge warning light
4. Went into FS Actions and disconnected ground power - and now the discharge warning light comes on.

Is that how it should be? I would have thought the battery discharge light should come on if ground power is switched off rather than fully disconnected, if electrical services are already draining the battery sufficient to light the amber warning?I couldn't find anything on this in volume 2 of the manual (at least not searching "battery discharge").David

[alvin 0]

As far as I remember this is beacuse the battery bus is powered by chargers (that are powered by GND power) (see the electrical system chart in FCOM2);what was puzzling for me in that scenario (gnd power connected, but switched off), was why battery is not charged, even though chargers are powered - Robert Randazzo replied that this is because battery tie breaker is opened when gnd power is off, and this mechanism is provided in order to protect the battery from overcharging.

[davierosoft 13]

The light will turn on if battery is not charging and it is (they are, in case of dual battery configuration) supplying current to the users.The logic is:95 seconds and current more than 5Amps are needed to turn on the light25 seconds and a current more than 15 ampsAbout 1 sec. for a current more than 100Amps.The battery chargers are powered by 3 phases AC power from the ground service bus (1 and 2 in case of dual batteries), they will convert 3 phase alternating current to DC power and charges the batteries.Now, The ground power supplies 115V 3phases, but to do that it is not sufficient to connect the cart to the plane.The ground power must be connected either in ground service mode (cabin lights, refueling and so on) or with the main power from the cockpit.You will see when it charges, discharges or is fully charged.Putting the Meter selector knob to BAT or AUX BAT will show you the draw of the battery. a minus before the number means that battery is supplying users, a 0 means that the battery is fully charged, positive values show that the battery is charging.There is a bit more in the logic including some charging exclusion in case of refueling and apu starting, but is a bit more...

[ajacied551 1]

The Battery(s) are charged from the battery charger(s), The Main Battery charger get's the 115V AC power from Ground service Bus 2 and the Aux Battery charger get's 115V AC power from the Ground service bus 1. There are 2 way's to get 115 VAC power on these Ground service busses (on the real airplane):* The normal way to get 115 VAC power on the Ground service busses is to get power from the AC transfer busses by switching ON the GROUND POWER or APU/ENG GENERATOR's switches on the overhead panel. * The Second way to get 115 VAC power on the ground service busses is to switch ON the GROUND SERVICE switch on the FWD attendant station, normally used to get some cabin lighting when cleaning the airplane.* On the NGX only the first way is simulated,* The second way is not simulated (correctly) There is no ground service switch simulated, The ground service busses are always powered on the NGX when the external power is connected, There is no way to switch the GROUND SERVICE bus(ses) to off and that's way the BATTERY DISCHARGE light will not illuminate when the external power is connected. The only way to unpower the Ground service is to disconnect the external power.

[davierosoft 13]

Nice finding, I never cecked the battery voltage/amp with GND power connected (as I rarely use it on ngx).Yes, it is not simulated or simulated in a way where te ground service is always connected (like if you, pilot, before entering in the cockpit, have turned the GND service on for the ground operations).However, also thinking this, there is an error with the APU start.In this way, with only battery applied, there is no amp draw from the battery when apu is started, and this is not possible as the APU must start from the battery bus (AC SERV BUS 1 is unpowered) and this is also one of the cases where the APU START Inhibit the battery chargers.Another little issue to add to te list ;)

[davidlondon 0]

Well, gentlemen, what an interesting series of responses. Very instructive. Thanks so much.Best wishes,David

[ajacied551 1]

However, also thinking this, there is an error with the APU start.In this way, with only battery applied, there is no amp draw from the battery when apu is started, and this is not possible as the APU must start from the battery bus (AC SERV BUS 1 is unpowered) and this is also one of the cases where the APU START Inhibit the battery chargers.Another little issue to add to te list ;)

There are two power sources capable to start the APU, DC power and AC power. To Start the APU on AC power the AC transfer Bus 1 needs to have 115 VAC power applied by the external power or Eng Generator power. If the AC power is not available on the AC Transfer Bus 1, The APU will start on DC power, The DC power comes from the 28 VDC Switched Hot Battery Bus, To get power on this bus just switch ON the Battery switch on the overhead panel.But during the APU start sequence only the main battery will supply 28 VDC to the Switched Hot battery bus. The Aux battery will not supply the 28 VDC to this bus due to fact that during the APU start the DUAL BATTERY RCCB will open to protect the aux battery from draining. You are right that the Main Battery Charger is not in the charge mode during APU start. But the Battery charger is in the TR mode. When the Ground service bus is powered the Main Battery charge will assist the Main Battery with the APU start, That´s why I think you see no negative ampere´s during APU start of the Main Battery, But I need to check this on the Real Airplane when possible.

[davierosoft 13]

The maximum load for the TR mode is 65Amps (just going with memory), a bit low to start the APU in TR mode.