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RUN THOSE AVIONICS!
It's inevitable. Low cost
computers and processing power has invaded the cockpit to stay. Rather than
dwelling over a chart on the kitchen table getting ready for that next
flight, the modern pilot will spend his afternoon sitting in the airplane.
Learning how to program, operate and configure his latest gizmo. Modern
avionics are so complex to learn and program, it literally takes dozens of
hours reading operating/user manuals while pressing the buttons just trying
to figure out what's important and what's not. Only after the pilot
completes this training, can he move onto safe flight, and even then, needs
to spend time in a powered up cockpit programming the avionics
1.
Run on the ships internal
battery. This is the
worst method, as it leaves you with a dead battery. 3. The best way is to use an external power supply system. This "system" includes the power supply itself, some wiring mounted in the airframe, and little knowledge. The benefits include: A. you can take it with you on trips as it's light weight (less than 2 lbs) or leave it behind. B. It belts out an impressive 13 AMPS of highly filtered and regulated DC power. It will charge a typical battery completely in 2 hours. It will charge a dead battery enough to start the engine in 15 minutes. C. It's VERY reliable.
D. The wiring added to
airframe allows instant connect and disconnect to a connector you place
wherever you want.
I built several different power
supplies for aircraft thus far. All power supplies have their pluses and
minuses. Some regulate well, but make a lot of VHF noise, others make plenty
of AMPS but their over current protection is so sensitive, it goes into
protection mode when connected to a run down battery. I've found the right
power supply and offer it to homebuilders as it meets all the needs. NOTE:
These are clean, tested, reconditioned units. If you want a new one, It will
cost you $165.
1 .Runs cool and quiet.
This is one of the units. It is
7" long, 3.5" wide and 2" high. Weight is less than 2 pounds so you can
throw it in your flight bag for those long trips. You can even permanently
mount it in you plane if you want. Installation guidelines The power supply is powered by a 3 conductor grounded cord and plug. As this unit draws little current from the mains, a small wire size is acceptable. I choose to use a small cord to make transporting this unit easier. This assumes and extension cord will be available whenever power is needed. You can make a cord of whatever length you like as long as you can get 2 amps thru it with minimal voltage drop. Connect the ground wire (usually green) to the FG (frame ground) terminal. This grounds the metallic housing of the power supply to prevent electrical shock if the unit were to malfunction. A loose rivet dropped into the power supplies cooling holes could also cause a dangerous short. Grounding is a must! Connect the cord's black wire to the AC(L) (LINE) terminal and the white wire to AC(N) (neutral) terminal on the power supply.
This completes the AC wiring portion of this unit. The power supply is internally fused so no external fuse is needed. The power supply has no on/off switch. You must unplug the unit to shut it off. Don't leave it plugged in unless it is under a load. This is a typical requirement of switching power supplies as they all like to have a load present whenever powered up. This power supply works well with little or no load, but you should still unplug it whenever it's power output is not needed.
WARNING
Connecting to the aircraft Connecting the power supply to the aircraft is a rather simple task. It's recommended that the output of the power supply be fed into the ships main DC bus via a 20 amp fuse. Builders wishing to connect other ways should do so carefully to insure the addition of this circuit to the ship wiring is done in such a manner as to prevent any power supply failures impacting the operation of the aircraft.
WARNING The -V terminal of the power supply should be connected to the aircraft ground, preferably at a common ground point if available. The +V terminal on the power supply should be connected to the 20 AMP inline fuse. This fuse is in turn connected to the ships battery bus. I recommend using a two pin MOLEX connector for this, but you may use whatever you like as long as it will flow 13 amps continuously without heating up. If you buy the kit, it comes with the connectors. I use some high current flexible 16 GA zip cord style wire purchased at any Radio Shack for the DC feeder cord. Keep the length around 6 feet to prevent excess voltage drop. The Radio Part number is# Why the battery bus and not the battery? The main reason is safety. NEVER connect anything to the hot battery bus unless absolutely necessary. In addition, if the power supply were to develop an internal leakage, this would present itself to you as a dead battery upon arrival at your aircraft. Connecting the power supply to the main DC bus has advantages. One is that you can power the avionics without a battery installed in the aircraft. You turn the master switch on which closes the battery contactor and begins charging the battery. In other words, you decide whether you want to charge the battery or not. Operating Instructions. Place the unit in a safe, level area away from flammable or other liquids. It is not waterproof or rain resistant. Don't use this unit outdoors if rain is likely. The unit should place in a area where air is free to circulate around it as it need air movement for cooling. Don't build it into a closed box as it will overheat and create a fire hazard. It will feel warm to the touch when operating at high loads. This is normal. A nice place to put it is on a stool on the hanger floor. Connect the power supply DC cord to the aircraft.
CAUTION Plug in the power supply to 120 Volts AC source. The aircraft DC bus is now powered. Turn on master switch. Leave master switch off is battery charging is not desired. Generally speaking, turn the master on as the battery will act as temporary power source during high load surges like firing up strobe lights, landing lights and big computers etc.
Remember, this power supply has
limits. If the battery was low, turning on the master switch will steal most
of the supply's output for charging. Switching on additional avionics at
this point will power the avionics, but leave little power for charging. You
can decide what you want. Most modern avionics systems will draw less than 5
amps total when operating. This leaves 8 amps for charging. Pressing the
transmit button on your transceiver will temporarily draw many amps. The
battery will make up for any power shortages during this type of transient
load. When this big load goes away, the battery resumes charging. You'll get
a feel for your aircrafts needs quickly. You may find you need to have the
battery on when raising the flaps since the flap motor startup load is too
much for the power supply and so on. |
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"He
who demands everything that his aircraft can give him is a pilot; he that
demands one iota more is a fool" |
