I have been practicing cold & dark procedures in the NGX, include some of the supplementary procedures.  I notices that NGX does not behave correctly when the Standby Power Test is performed.

 

The check begins with the Battery switch ON and the AC-DC meter selectors  set to STBY PWR.  The DC volts reads 26 volts. 

 

If the APU generator or the ground power is on, then the APU GEN No 1 and No 2 switches are set to OFF and the GRD PWR is set to off, placing the aircraft on battery power only.  When the aircraft is on battery power only, the voltage increases to 28 volts.

 

The STANDBY POWER switch is then placed to OFF, the AC and DC volts should read 0, which they do. Then, the procedure calls for setting the STANDBY POWER switch to BAT, directly connecting the battery to the standby power system.  Per the Boeing procedure, the DC volts should read 24 +/- 2 volts.  However, in this configuration, the DC volts reads 28 volts.   The procedure then calls for selecting BAT & AUX BAT voltage, both of which should read  24 +/-2 volts, plus a battery amp discharge indication. Once again, the BAT and AUX BAT volts reads 28 volts.

 

When the APU GEN #1 and #2 are placed back ON, the DC volts drops to 26 volts.

 

If the cold and dark panel state is loaded and battery voltage is first checked, the DC volts correctly reads 24 volts.

 

It appears that DC volts may not be correctly modeled when the aircraft is on battery power only at point after a generator is selected and the transfer busses are powered.

 

I am not familiar enough with the B737NG to know if how NGX behaves is correct, but it does not appear to be in agreement with the Boeing supplementary procedure.

 

Thanks!

 

Rich Boll

Wichita, KS

Very interesting i'll check this tonight and report back!

When you load cold and dark check to make sure you don't have the wheel chokes in place and do the test again!

wheel chocks were in place.

 

I also tried the test with the airplane powered with just ground power (APU not running) and got the same results.

 

However, If I do check before connecting ground power or APU generators to the transfer busses, the check works correctly.  The DC volts reads 24 volts. 

 

I tired something different.  I did the check with just the batteries ON. The DC volts read 24.  Then I connected ground power using the LSK under FS ACTION, but did not connect the ground power to the aircraft using the GND PWR switch.  Here's what I saw:

 

1. BAT BUS = 28V DC

2. BAT  & AUX BAT = 24V DC & 0 DC AMP (battery not discharging, which may be correct because the battery chargers are being powered?)

3. STBY PWR = 28 V DC

 

Is the battery bus (BAT BUS on the DC electrical panel) powered by ground power when the GRD PWR is switched off?

 

Thanks,

 

Rich

If you have the wheel chocks in place you won't get the batt discharge come on as they charge the AC ground service bus. Is this what you are looking for?

 

Once i get home i'll check it all up