1. Electrical Systems

2. Choice of Battery CAPACITY NUMBER TYPE
Must adequately supply all power requirements
Extra margin for battery deterioration (x2) by temperature and age
NUMBER
Twin battery only where heavy and continuous power needed
Twin batteries should be switch selectable and not wired in parallel
TYPE
Batteries must be sealed, non spill gel type

3. Battery Plugs and Connections
Fuse in positive cable as close as possible to battery (this is VITAL)
Battery wiring to carry fuse blow current easily
Insulation of wiring from fuse to battery must be perfect and short circuiting virtually impossible
Battery connections must be rugged, protected against fatigue and terminals thoroughly insulated
Preservation of polarity – foolproof standard plug
Impossible to short live battery plug
ALL SUBJECT TO MECHANICAL STRESS AND ABUSE

4. The Humble Fuse - 1
Provides low-cost, reliable protection against overloads and fire – a real lifesaver
Correct rating depends on MAXIMUM normal load in circuit (use 1.25 x max normal load as a guide)
NB High currents during radio transmit or A/H startup
Circuit must NEVER be at risk even at 2x fuse rating
Choice of fuse and wiring should be made together.

5. The Humble Fuse - 2
Good quality fuse holder with fuse rating clearly marked
May be in-line or panel mounted (preferable)
Ensure voltage drop across fuse is acceptable at max normal load
Ensure plentiful supply of correct fuses in cockpit, all clearly marked
Fast blow and slow blow fuses have different applications and are NOT interchangeable
Slow-blow fuses withstand temporary startup overloads

6. Cable Polarity and Security
Red for Positive
Black for Negative
Secure to structure and not to control systems
Protect from abrasion, not too tight, provide proper support

7. The Hostile Cockpit Instruments and wiring are subject to:
Vibration and maltreatment
Dirt
Moisture and Corrosion
High and low temperatures
To function Reliably, wiring must be:
Tidy
Strong
Protected
Properly joined
Capable of carrying the load
Safe from catching fire
Checked regularly

8. Instrument Panel Electrics
POWER
Main supply plug – robust, low resistance, high capacity, polarised
Battery Select – ON-OFF-ON, capacity related to fuse
Main switch – isolates all circuits, on-off, UP for ON
Distribution block – low resistance, room for expansion
INSTRUMENTS
Fuses and switches – placarded ON/OFF, fuse rating and function
Wire thickness and fuse related to upstream fuse and to load
Protection and insulation of all terminals – FOD
Plug to allow easy removal of instrument panel
Plug or terminal block allows for instrument removal for service
Tidy colour-coded and circuit diagram to aid servicing

9. Wiring to the ‘stick Examples: Press to Talk, cruise-climb
Use very good quality, multistrand cable
Run through ‘stick where possible for protection
Across moving segments – sufficient cable so as not to obstruct but not enough to catch on other moving parts
Cable-tie securely and cut off neatly
Test very carefully in all possible combinations of control positions

10. Ohm’s Law Voltage = Current X Resistance (V=IR)
Current = Voltage/Resistance (I=V/R)
Resistance = Voltage/Current (R=V/I)
Units Volts, amps and ohms

11. COMPONENT CHOICE Good quality, new components give little trouble
Other sources apart from automotive suppliers:
Dick Smith (limited range with variable quality of advice)
Altronics
Jaycar (Newcastle Street)
RS Components (cheapest, wide range, little advice and bulk purchases)
Cost of good, new parts is tiny compared to cost of finding a pesky fault in cheap or second-hand parts
IF IT’S WORTH DOING, ITS WORTH DOING PROPERLY