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LR3D Technical Manual
Rev. IR (5/13/2020)
The LR3D is an external alternator controller (regulator) designed for use with B-type, wound-
field alternators. Over-voltage (OV) protection, Low-Voltage (LV) warning output, and field-
adjustable charging voltage are integrated into the LR3D control package.
1 - Battery Temp input (optional)
2 - Over-Voltage Test input (optional)
3 - Bus Voltage Sense input
4 - Field output
Terminal 1 – This input, when used with the optional temperature probe, will enable the LR3D to
automatically adjust the alternator output voltage as the temperature of the battery terminal
changes. Because the ideal charging voltage for a battery is dependent on battery temperature,
some operators may desire a higher charging voltage during winter operations and a lower
charging voltage during summer operations. While this can be accomplished by manually
adjusting the voltage regulator, the intent of this feature is to make the adjustment occur
automatically from one season to the next. In practice, the vast majority of installations do not see
a wide enough swing in battery temperature to justify the added expense and complexity of the
temperature probe.
Terminal 2 - This input is used to verify the function of the crowbar OV protection circuit in the
LR3D. If aircraft bus voltage is momentarily applied to this terminal, the LR3D will interpret it
as an OV event and will trigger the crowbar circuit, causing the 5A Alternator Field circuit
breaker to open just as it would for an actual OV condition. This test may be performed during
the annual condition inspection of the aircraft using a jumper wire or test lead. Fixed wiring of
this feature is uncommon and not recommended.
B&C Specialty Products
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INTRODUCTION
OVERVIEW
5 - Low-Voltage Warning output
6 - Bus Field Supply input
7 - Ground input
Case Ground & Voltage Adjust (not shown)
Section A
Introduction
Page A - 1
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