Electronics International VA-1A - Manual (Page 7)

B. Turn on the piece of electrical equipment you wish to check.
C. If this piece of electrical equipment is working properly, you will see an increase 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
the amps 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 select switch in the “Volts” position, the VA-1A will display the bus voltage to .1 volts. With
all electrical equipment off and a fully charged battery the bus voltage will be around 12.1 to 12.5 volts
(double these levels for a 24-volt system). Each battery has its own operating voltage when charged. As the
battery gets near the end of its life, this voltage will start to drop. A discharged battery will also run at a
lower voltage. Don’t confuse a good discharged battery with an old battery.
2. Master On, Engine On: 2. Master On, Engine On: 2. Master On, Engine On: 2. Master On, Engine On: 2. Master On, Engine On:
The following describes the operating characteristics of the VA-1A installed in the battery lead with the
master switch on and the engine on.
With the Mode Switch in the “Amps” position, the VA-1A will display the charging current to the battery.
When the engine is first started, the current will jump up to 20 amps or more and will quickly decrease as the
battery takes a charge. Within a few minutes, the charging current will have dropped to 6 amps or lower and
will continue to drop for the next hour until it settles to 1.0 amps or lower.
With the VA-1A installed in the battery lead, load current cannot be monitored during flight. The Alternator
(or generator) is supplying all of the electrical load and charging the battery. Only the battery charging
current can be monitored for this installation.
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.
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Operating Instructions Operating Instructions Operating Instructions Operating Instructions Operating Instructions VA-1A Installed in the Battery Lead VA-1A Installed in the Battery Lead VA-1A Installed in the Battery Lead VA-1A Installed in the Battery Lead VA-1A Installed in the Battery Lead