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-   -   Garmin Heated Pitot wiring (https://vansairforce.net/community/showthread.php?t=131112)

Jake14 10-31-2015 08:33 PM

It would be simple to isolate the controller box from the wing and run all grounds back to the panel twisted with the power cable. I'll see if I can get Dynon's opinion on the optimum method

penguin 11-01-2015 05:48 AM

There are a few basics that bear thinking about here,

- Shielded cable is used to prevent RF interference and has no influence on magnetic interference (woven iron shielding is required - heavy and not that efficient).
- Taking a ground wire back to a single point is to avoid 'ground loops' and interference on the audio system - typically from AC and high frequency switched devices (doesn't sound like a heated pitot to me).
- Local grounds are used to save weight - sounds useful when a 14 or 12g conductor is required.
- Wire gauge depends if the conductor is bundled or not and the length of the conductor (potential volts drop), use the thinnest conductor to save weight.
- Weight saving in all aspects of the build is key to achieving good overall aircraft performance (in any aircraft).

Use a single conductor of adequate thickness for the length and ground to a wing rib. Position a magnetometer far enough away from the pitot that it is not affected (AP servo same side as pitot with magnetometer in the opposite wing or rear fuselage). I believe Garmin install manual shows magnetometer under the HS fairing? Shielded cable and running a ground back to the forest of tabs is just heavy for no performance benefit.

Pete

PS my (biased) opinion is Safeair 1 produce a better pitot mast than Gretz

Jake14 11-02-2015 01:22 PM

to follow up: talked to Dynon and they said both power and ground wires should definitely both be run back to the panel (no local ground). They stated that their controller case is not grounded, (so I guess the current in the ground wire should match that in the power lead). I'll check the case ground to make sure after I get the wiring hooked up.

So I plan on twisting the black and red (14ga) wires together with the white 18ga wire and running them separately (not in a bundle) back to the panel, keeping as far as possible from the AHRS/magnetometer.

JDA_BTR 11-02-2015 05:47 PM

I guarantee you that the controller box is grounded. 0 ohms between the black ground wire and the box. It is so by design as the mosfet that controls the heater current is heat sinked to the box, and that part of the mosfet is ground.

The controller box ground as the main ground is not adequate, as you would not want to ground the whole board via the mosfet heat sink, hence the separate wire. But grounded it is nonetheless.

Jake14 11-04-2015 12:51 PM

yup, you're right, the box is grounded. Dynon is working on a recommendation

JDBoston 11-04-2015 02:31 PM

Just to close the loop on my side, I am going with running two wires back to the panel (three if you include the signal wire for the regulator) vs grounding locally.

I asked Vans and they stated that they have no current options, and that in the future there may be some sort of guidance with the avionics packages but those will be through vendors vs shipped via vans.

Garmin told me that they recommend running a ground wire back to the main panel.

Thanks for all the advice.


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