From: "Sid Lloyd" <glastar1@swbell.net>
>
>I want to use one of the B & C Specialty Products lightweight alternators
and
>their regulators. They offer both a 60 and a 40 amp version. How do you
>know which one to get? Do you add up your planned electrical load and
>figure it out that way?
>
>Thanks,
>
>Sid
You need to accomplish what is called a "load analysis" for
the various phases of flight. Some folks do it on a spread sheet
and enter continuous running load (transmit doesn't count, lowing
landing gear
generally doesn't count, only add up loads that are on for duration
of the flight phase).
Main Bus Loads
Pre- Taxi Climb VFR IFR Decent
Taxi Alt
Flt Cruise Cruise
Out
Battery contactor 1.0 1.0 1.0 1.0 1.0
1.0
Engine Gages 0.3 0.3 0.3 0.3 0.3
0.3
Strobe Lts 2.5 2.5 2.5 2.5
2.5
Nav Lts
Fuel Pump
Landing Lt 7.5
Taxi Lt 4.5
Pitot Heat 5.0
Main Bus Totals
Essential Bus Loads
Pre- Taxi Climb VFR IFR Decent
Taxi Alt
Flt Cruise Cruise
Out
Com 0.1 0.1 0.1 0.1 0.1 0.1
0.1 0.1
GPS 0.2 0.2 0.2 0.2 0.2 0.2
0.2 0.2
T/C 0.3 0.3 0.3 0.3 0.3 0.3
0.3 0.3
Transponder/Encoder 0.45 0.45 0.45 0.45 0.45 0.45
0.45 0.45
Map Lt/Pnl Flood 0.1 0.1 0.1 0.1 0.1 0.1
0.1 0.1
E-Bus Totals 1.25
The list above is not intended to be all inclusive nor are the figures
entered intended
to be representative of your airplane . . . you need to do the homework and
get all the
data approprate to the equipment you plan to use.
You might also include a column headed NITE VFR . . .
After all the continuous loads are added up, total loads for E-Bus and Main
bus
should not be so great in any class of operation such that it doesn't leave
10A
or so to recharge your battery. The FAA uses a rule-of-thumb on the order
of 20
percent of alternator output should be reserved for battery charging. A better
rule is to figure out how much snort it takes to completely recharge your
battery
in 1 hour of flight. If you have an 18 a.h. battery, then you need 18A of
extra
output over and above your max continuous running loads.
If you make it an operating rule for your airplane that you will NEVER depart
into potentially stressful flight conditions unless the battery is fully
charged,
then you don't need to meet the 1 hour "rule" . . . If on hopefully very rare
occasions that you find your ship's battery totally dead, you make sure the
battery
is mostly recharged before launching into the blue then you can sensibly
mitigate
your alternator requriements. The classic rules of thumb observed by certified
aircraft designers originat from the padded cockpit environment where the
pilot
is assumed to know nothing about how the system was architectured or how it
operates. You are all encouraged to understand what's happening, why, and
be able to operate comfortably with it based on purposeful decision making.
I'm not sure the chart above will pass through all of the various lists with
the columns intact so I've dumped this e-mail to a .pdf file which you may
doanload at http://www.aeroelectric.com/articles/loadanal.pdf
Bob . . .
Bob . . .
--------------------------------------------
( Knowing about a thing is different from )
( understanding it. One can know a lot )
( and still understand nothing. )
( C.F. Kettering )
--------------------------------------------
http://www.aeroelectric.com
|