Ok IF my understanding is correct, the APU supplys AC to power the aircraft. So, in the su2 will the APU keep the battery from runig down?And if the APU doesn't keep the battery charged, will the ground pwr keep it charged? Or is thier another way to keep the battery charged (other then FSCUIP). It is rather challenging to go down the checklists when the batter keeps discharching. And If yall havn't thought about it..... Well... Just a thought.

Don't forget to sign...U might not get a response...Troy

Mystry poster,Battery drain has been fixed.

Sorry, I hit the submit button twice.

Hey, If the APU is running on the ground, why would the battary discharge? Presumably the battary will be drawing from the battary bus thus charging whilst the APU is powering aircraft system. Thus the battary won't be supllying any electrical energy to any part of the aircraft. If your battary is discharging, then you mustn't have your APU Generator on-line. Beware I may have used some "Bus" terms in here...

http://www.jet-precision.com/Uploads/MM-JPS.jpg

Ok Thanks for the heads up! thats the in formation.DavidAkA Mystry Poster

"If the APU is running on the ground, why would the battary discharge?On "regular" aircraft, it shouldn't, William, but...After APU start, the 737NG's Battery Charger automatically senses that the battery has been partially depleted, so it should start recharging the battery using main bus power. However, some things will stop the battery charger from operating (APU start itself, the Wing Station Refuelling Panel being open, Battery overheat, Standby Power Switch In BAT position, etc). On quick turnarounds, the fuelling panel may remain open for most of the transit, especially if the fuel uplift is large. Depending on when the APU was started, I can't see this as being much of a problem however. "Presumably the battary will be drawing from the battary bus thus charging whilst the APU is powering aircraft system. Thus the Main Bus power when available... in this case, from the APU Generator). Recharging will only occur if there is main bus power. battary won't be supllying any electrical energy to any part of the aircraft."You may find the 737NG electrical system somewhat unique (and very difficult to describe without the aid of diagrams). Normally the Battery Charger will be providing the HOT and SWITCHED HOT BATTERY Busses with power (operating in "TR" mode... i.e. Transformer-Rectifier mode). The 737NG's (Main) BATTERY BUS on the other hand, is usually powered by TRU #3 (Transformer-Rectifier Unit #3). The aircraft has 3 TRU's as well as the Battery Charger TR function. With the meter panel in the BAT position, the meter shows either Battery voltage or Battery Charger Voltage, whichever is highest. This meter voltage value should reflect the voltage on the HOT and SWITCHED HOT BATTERY Busses, not the traditional "BATTERY BUS". Normally (it seems) the BATTERY BUS is not tied to the HOT and SWITCHED HOT Battery Busses. I stand to be corrected by the real 737NG experts, however ;-) There aren't too many systems connected to the HOT and SWITCHED HOT Battery Busses, so the battery shouldn't deplete too fast even with the Battery Charger disabled.Here's some additional info:According to the 737NG maintenance manual, the battery can be in one of four(4) states. Discharge, Charge, Overcharge and Trickle Charge.Discharge is whenever the battery is being used (e.g. This can be anything from milliamps for running the chronometers, to tens of amps.... e.g. during APU start).Normal charging is in the form of a constant current (38Amps) with a rising variable voltage. At a certain point, the charger will switch to a trickle charge (This is the "overcharge" period. This ensures that the battery is well and truly charged). After this period, the Battery Charger goes into a Transformer-Rectifier (TR) mode, outputting a constant 27.5 Volts. The HOT BATTERY and SWITCHED HOT BATTERY Busses use this voltage under normal circumstances.The Battery Charger will start charging again if the battery voltage drops below 23volts (the battery has a "nominal" voltage of 24Vdc) or if power is removed from the Battery Charger for more than a second.Note that heavy battery discharge will usually cause the BAT DISCHARGE light to illuminate and Master Caution "ELEC" message to illuminate, but this is inhibited during APU start.Hope this helps.Cheers.Ian.

Thanks for the APU 101! :D

"Thanks for the APU 101! :D"You're welcome, David :-)...Except I may have to bring out "102" :-P ... I just discovered something in the manuals... so I have to correct the following statement..."...some things will stop the battery charger from operating (APU start itself, the Wing Station Refuelling Panel being open, Battery overheat, Standby Power Switch In BAT position, etc). On quick turnarounds, the fuelling panel may remain open for most of the transit, especially if the fuel uplift is large. Depending on when the APU was started, I can't see this as being much of a problem however."Those things which I thought would stop the Battery Charger from operating, actually don't stop the Battery Charger from operating completely. With the Wing Station Refuelling Panel open, with Battery Overheat, etc, this stops the Battery Charger from being a battery charger, but this don't stop it from being a Transformer-Rectifier. This means that the busses will still get full power from the Battery Charger... and the Battery, as far as I can see, shouldn't deplete at all.Hope this makes sense.Cheers.Ian.