Master Relay & Starter Relay Protection Diodes

[Rob Hickman]

All aircraft must have protection diodes installed on their Master Relay, Starter Relay and any other large relay. If your aircraft does not have the protection diode on the Master Relay your electrical buss will experience a voltage spike of 500+ Volts every time you turn off the master switch. If your EFIS or Engine Monitor is wired directly to the electrical buss it will be the device that absorbs the voltage spike and will eventually fail. All users must verify that they have the protection diodes installed before powering the EFIS or Engine Monitor from the electrical buss.

Van’s Aircraft sells the protection diodes and they can be found using the following link:

http://vansaircraft.com/cgi-bin/catalog.cgi?ident=1244562062-496-216&browse=electrical&product=diodes


Surge protection diode for Master Switch
Part Number = ES DIODE MASTER
Price = $5.65

Surge protection diode for Starter/Mag Switch
Part Number = ES DIODE STARTER
Price = $5.65

[jperryfly]

You can also get the diodes from Radio Shack. I got two 3amp/200PIV diodes for $1.59. Some ring connectors and shrink tubing and you're good. The banded end goes to the battery terminal on the relay and the other end goes to the small terminal that is connected to your master switch. See the The Electrical Connection.