Overvoltage Protection Relay Driver (Rev G-TH)
author: Eric
2 layer board of 1.71 x 1.63 inches (43.4 x 41.4 mm)
Uploaded:
May 08, 2025
Shared:
May 17, 2025
Total Price:
$13.90
Description: This board is as adaptation of the “OVM-14 Mk III Overvoltage Protection Module” designed by Robert L. Nuckolls III, as posted to the AeroElectric-List forum. The board provides overvoltage protection for the charging system in an Experimental category aircraft. It’s a relay driver instead of a crowbar; it opens relay(s) to interrupt the alternator field supply or the AC feed from a permanent magnet stator. It adds several features that are absent in the original version:
- EFIS alarm output. Sends a 10V (3mA limited) signal to an EFIS alarm input to notify the pilot that the module has tripped.
- Flashing OVP TRIP indicator LED output. 1.5Hz (20mA limited) output to flash an indicator LED on the instrument panel.
- PUSH ISOLATE switch. Allows pilot control of a permanent magnet stator feed (as in a Rotax 9-Series engine installation) and pilot reset of the module in the event of a nuisance trip.
The nominal trip voltages are 16.0V in normal mode and 13.7V in maintenance test mode (both values subject to 1% resistor tolerance). The design is tested and working; see performance on the last two pages of the documentation PDF.
This project is intended for use in Experimental category aircraft only. Do NOT install it in a CAR Part 3 or FAR Part 23 certificated aircraft without FAA Field Approval.
BOM: Cost is ~$13 for the components to populate this board, plus builder’s choice of PUSH ISOLATE switch and indicator LED. Click for a Digi-Key saved list with required and suggested parts.
Download: Click here for a .ZIP archive containing full documentation in PDF format, DipTrace v5.1.0.3 CAD files and RS-274X Gerber files.
Description: This board is as adaptation of the “OVM-14 Mk III Overvoltage Protection Module” designed by Robert L. Nuckolls III, as posted to the AeroElectric-List forum. The board provides overvoltage protection for the charging system in an Experimental category aircraft. It’s a relay driver instead of a crowbar; it opens relay(s) to interrupt the alternator field supply or the AC feed from a permanent magnet stator. It adds several features that are absent in the original version:
- EFIS alarm output. Sends a 10V (3mA limited) signal to an EFIS alarm input to notify the pilot that the module has tripped.
- Flashing OVP TRIP indicator LED output. 1.5Hz (20mA limited) output to flash an indicator LED on the instrument panel.
- PUSH ISOLATE switch. Allows pilot control of a permanent magnet stator feed (as in a Rotax 9-Series engine installation) and pilot reset of the module in the event of a nuisance trip.
The nominal trip voltages are 16.0V in normal mode and 13.7V in maintenance test mode (both values subject to 1% resistor tolerance). The design is tested and working; see performance on the last two pages of the documentation PDF.
This project is intended for use in Experimental category aircraft only. Do NOT install it in a CAR Part 3 or FAR Part 23 certificated aircraft without FAA Field Approval.
BOM: Cost is ~$13 for the components to populate this board, plus builder’s choice of PUSH ISOLATE switch and indicator LED. Click for a Digi-Key saved list with required and suggested parts.
Download: Click here for a .ZIP archive containing full documentation in PDF format, DipTrace v5.1.0.3 CAD files and RS-274X Gerber files.
