Electronics International VA-1A User Manual

Page 9

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Operating Instructions

VA-1A Installed in the Alternator Lead

With the Mode Switch in the “Amps” position the VA-1A will display the electrical system load on the
aircraft plus the battery charging current. Since the engine is on, all of the current is being supplied by the
alternator. The VA-1A will show a charging condition (the “Discharge” light will be off) and display an
accurate reading of the total current drain from the alternator. In this mode of operation any piece of electri-
cal equipment can be checked for proper operation during flight by performing the following steps:

A. Note the amps reading on the VA unit.

B. Turn off the piece of electrical equipment you wish to check.

C. If this piece of electrical equipment is working properly, you will see a decrease in load current that
corresponds to the current that piece of equipment requires. Compare this current with the current you
measured for that same piece of equipment at an earlier date.

Using this method with the digital display of the VA-1A, many important aircraft functions (strobes, retracts,
radios, transponder, ADFs, DMEs, pitot heat, etc.) can be checked from the pilot’s seat. It would be worth-
while to write down the load current for the entire system and for each piece of equipment. This would give
you something to compare to when you wish to check for proper operation at a later date. You may also
check the entire electrical system with one check by turning all the electrical equipment on and comparing
this reading with your normal reading taken at an earlier date. If an improper reading is noted, the VA-1A
may then be used to diagnose which piece of equipment has malfunctioned by checking each piece of
equipment separately.

With the mode selector switch in the “Volts” position the VA-1A will display the bus voltage to .1 volts.
With the engine running the alternator is capable of raising the bus voltage to a dangerously high level. It is
the voltage regulator's job to limit the bus voltage between 13.5 and 14.8 volts (double these levels for a
24-volt system). Look for this level on the VA-1A. A low voltage reading will cause the battery to charge
very slowly. A high reading can damage the battery and most of your electrical equipment. If the aircraft
bus voltage goes to a dangerously high level (15.3 volts or higher) a bright red “High Volts” light on the VA-
1A will warn you of this condition. If this happens turn the field to the alternator off to eliminate the over
voltage condition.

Another common electrical problem is a discharging condition. If this condition goes unnoticed (which it
normally does) you will end up with a dead battery in flight rendering all of your electrical equipment
useless. To help you avoid this situation the VA-1A has a “Discharge” Warning Light which acts as an early
warning to alert you as soon as the battery goes into a discharging condition. If this situation occurs, turn off
any unnecessary electrical equipment. The lower you can get the discharging current, the longer the battery
will last. With the VA-1A installed in the alternator lead, discharging current cannot be monitored.

The VA-1A will display trend information when your battery is in a discharging condition. As you watch the
battery discharging .1 volts at a time, it becomes relatively easy to judge the remaining time you have before
the battery reaches a seriously low condition. As the battery voltage approaches 11 volts (22 volts for a 24-
volt system), the aircraft’s electrical equipment will start to malfunction. The exact voltage at which each
piece of equipment will start to malfunction depends on the design of that equipment. The VA-1A will work
accurately from 40 to 7 volts--far below where most electrical equipment starts to fail.

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