Received Isolation Diodes

Six of my devices will be connected to an essential bus in addition to the VP-X.  This provides an alternate power path for the most critical flight instruments and eliminates several single points of failure in the electrical system:

  • Master switch
  • VP-X
  • Master contactor
  • Various wiring downstream of the master contactor

The essential bus pulls power directly from the battery bus through a high current switch and into another fuse box.  Since there are two power paths for each device, I need to use a diode in each supply line to prevent back feeding power through either the VP-X or the essential bus fuse box.  A common cathode schottky barrier diode pair in a TO-247 case would be perfect from a power standpoint, but there are two problems with those devices.  The first is that the case is electrically connected to the cathode, so it must be insulated from the heatsink with a mica washer.  The second problem is that the TO-247 leads need to be installed in a circuit board and the connections must be soldered.  Instead, I chose these schottky barrier diode pairs in an ISOTOP package.  These will be perfect for the job.  The case is electrically isolated from the diodes, so I can mount these directly to the subpanel to ack as a heatsink.  They’re also rated at 40A continuous (per diode), so I won’t be anywhere near the thermal capacity of the diodes.  The only downside to these devices is that the cathodes must be connected externally, but that’s a minor issue.

The six devices that will be connected to the essential bus are:

  • Left SkyView Screen
  • Audio Panel
  • GTN Main Power
  • GTN COM Power
  • SkyView Autopilot Servos
  • TruTrak Gemini

Here are the diode packs I’m using.  I found them at mouser.com for about $25 each (I need 6).

I also installed a WDG3 adel clamp below the ARINC-429 converted box to support the wires and keep them from rubbing the subpanel.

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