Electronics International VA-1A Volts/Amps Internal or External Shunts
From Electronics International, Inc.
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VA-1A vs VA-1A-XX
In order to accurately monitor amps in an aircraft, a voltammeter must have a shunt through which aircraft current flows. This shunt is built into the VA-1A, meaning you do not have to purchase a shunt with the VA-1A. The VA-1A-XX (where “XX ” is the value of the shunt), on the other hand, must be connected to an external shunt. Be sure to specify what your shunt value is when ordering. If you aren’t certain, download “Determining Your Shunt Value” for steps on how to locate what shunt you have installed on your aircraft.
The VA-1A is a Primary Replacement, FAA STC’d instrument.
Size (H x W x D)
2.5″ x 2.5″ x 2.5,” with a 2.25″ Bezel
Instrument – 9 oz.
S-50 Shunt – 3 oz.
S-300 Shunt – 12 oz.
7.0 to 40 Volts, 2/10 Amp
Viewable in direct sunlight, with dimmable 12 and 24 volt backlight control lines.
1% of reading +/- one count
VA-1A and VA-1A-XX (60 Amps and below for “XX”) resolve amperage to .1 amps. VA-1A-XX (above 60 for “XX”) resolve to 1 amps. All units resolve voltage to .1 volts.
Contains an internal shunt for measuring current to 100 amps and voltage to 40 volts.
This unit must be matched to the aircraft’s external shunt. The shunt value is determined by how many amps must pass through the external shunt in order to achieve a 50mV drop across the shunt leads (i.e., 100 amp, 50mV external shunt would be matched to a VA-1A-100, a 70 amp, 50mV external shunt would be matched to a VA-1A-70, etc…).
Not only do the VA-1A and VA-1A-XX provide pilots with precision voltage (to .1 volts) and Amps (to .1 Amps), but it keeps a watchful eye on the electrical system. Both systems have a “Discharge” light for low voltage situations, as well as a “High Voltage” warning light for over-voltage situations.
The systems also come complete with an external warning line that can be attached to a warning device, such as an Electronics International AL-1 Warning Light, AV-17 Voice Annunciator or ATG-1 Tone Generator, or myriad other warning devices.
Discharge Warning Light
For a 12 volt system, the light will be on when bus voltage falls below 12.8 volts (+/- .2 volts). For a 24 volt system, the light will be on when the bus voltage falls below 25.6 volts (+/- .4 volts). The voltage signal is picked up on the red power lead to the instrument.
High Volts Light
For a 12 volt system, the light will be on when the bus voltage exceeds 15.4 volts (+/- .3 volts). For a 24 volt system, the light will be on when the bus voltage exceeds 30.8 volts (+/- .6 volts). The voltage signal is picked up on the red power lead to the instrument.
External Warning Line
Both the VA-1A and VA-1A-XX have an external warning line that activates during a “High Volts” or “Discharge ” scenario. The line is normally open, but when activated, it pulls to ground. You can hook the external warning line to any Electronics International warning device, such as an Al-1 warning light, AP-7 Annunciator Panel, ATG-1 Tone Generator or the AV-17 Voice Annunciator.
12/24 Volt Switch
A selector switch is located on the back of each VA instrument, which allows the instrument to be configured for either a 12 volt system or 24 volt system.
(VA-1A or VA-1A-XX) Instrument
Installation and Operating Instructions.
100 Amp, 100 mV.
Order the S-50 for a VA-1A-50 if you don’t already have a shunt
300 Amp, 50 mV
Order for a VA-1A-300 if you don’t already have a shunt
The VA-1A and the VA-1A-XX both have shunts. By measuring the voltage drop across a shunt, the VA-1A and VA-1A-XX can determine how much amperage is being loaded on the aircraft’s battery or alternater/generator.
The VA-1A has an internal shunt, and the VA-1A-XX requires an external shunt. For the VA-1A-XX, the “XX” equals the value of the shunt. To determine the value of your aircraft’s shunt, visit the Downloads section of the VA-1A and download the sheet entitled “Shunt Value.” The VA-1A-XX can be custom built to match your aircraft’s existing shunt.
Most people who are replacing their existing Voltammeter will replace it with a similar type (internal or external). Internally shunted systems generally have large lugs at the back of the instrument (this is part of the internal shunt), while externally shunted instruments have small wires that leave the back of the instrument.
Used with the VA-1A-50.
For amperage loads up to 100 Amps.
Used with the VA-1A-300.
For amperage loads up to 300 Amps
The RSVA-3 allows pilots to switch between three shunts for a twin engine application. The switch will select between Left Alternator (or Gen), Right Alternator (or Gen), and Battery shunts. This allows the pilot of a twin engine aircraft to monitor all loads on the aircraft system with only one instrument.
Shunts are not included in the RSVA-3 price and must be purchased separately.