Va-1A Installed In The Alternator Lead - Electronics International VA-1A Operating And Installation Instructions

Operating Instructions
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 electri-
cal equipment useless. To help you avoid this situation the VA-1A has a "Discharge" Warning
Light which acts as an early warning, alerting you as soon as the battery goes into a discharging
condition. The amount of discharging current can be displayed in the "Amps" position. Discharg-
ing current will be displayed as a minus number. If this situation occurs, turn off any unnecessary
electrical equipment. The lower you can get the discharging current, the longer the battery will
last.
The VA-1A will display trend information when your battery is in a discharging condition. As you
watch the battery discharging 0.1 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 ap-
proaches 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.
Two common methods of installing the VA-1A or VA-1A-XX in the electrical system of your aircraft
are in the battery lead and in the alternator lead. Following are the operating characteristics of the

VA-1A installed in the alternator lead.

1. Master On, Engine Off
The following describes the operating characteristics of the VA-1A installed in the alternator lead
with the master switch on and the engine off.
With the Mode Switch in the "Amps" position the VA-1A will display 000 (+/- a few counts). Since
the battery is supplying all of the electrical load and the alternator is off (not turning), there is no
current being supplied from the alternator and the "Discharge" warning light will be on.
With the mode select switch in the "Volts" position, the VA-1A will display the bus voltage to 0.1
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
The following describes the operating characteristics of the VA-1A installed in the alternator lead
with the master switch on and the engine on.
VA-1A Installed in the Alternator Lead
VA-1A Installed in the Battery Lead
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