Compass Location

Hi Guys
This last weekend I notice when the master switch is activated the compass swings 10 deg. and when the landing lights are turn on the compass swings another 20 deg. Short of re-locating the compass is there a remedy for this?

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compass on the left side over the main power bus.

you could try the ACS demagnetized box or similar-- it's a piece of sheetmetal that you bend or wrap around areas to prevent compass swing.

I thought you wrap it around the compass but that didn't work for me. they say you locate it where it helps the most. ( my problem was I mounted a huge stereo speaker behind the panel and the 40oz magnet was throwing everthing off.) removing the speaker helped the most.



about $15.00 for a piece of sheet metal. I'm not sure whether it demagnetizes of makes everything a little bit more positive.

sorry can't find it in ASC.

Sounds like you have at least identified which wires are causing the trouble. You could try some shielded wiring or rerouting the wiring to move it away from the compass, but that may not be an option, in either case.
I had a similar problem and ended up switching the compass with another instrument, which worked ok.
In your case, maybe move it over and up one. The other two gauges would be in a horizontal rather than vertical row and the compass farther away from the wiring.
Good luck.

BUT, then it would be closer to the tach. (a rotating magnet). Might be worth a try.
Mel...DAR

What did you switch?

sf3543 said:

I had a similar problem and ended up switching the compass with another instrument, which worked ok.

Click to expand...

Curious what you switched. Did you just replace the compass with another type of compass, or do you mean you swapped the compass' location with another instrument you already had?

Curious what worked for you. I have a wiring-induced compass interference thing going on in my panel, too. My Dynon with its remote EDC works perfectly, but the Precision vertical card compass in my panel is basically worthless.

)_( Dan
RV-7 N714D (622 hours)
http://www.rvproject.com

Compass Interferance

Hi Dan

I explained my compass deviation problem to the electronic engineer at work. He advised me to wrap all the power wires with aluminum tape and ground one end of the tape. He is confident that any magnetic field generated by power in the wires will be shielded by the tape. I will post photos and the results later this week.

Aluminum tape?

Aluminum tape will confine any RF that might be on the wires, but I don't believe that it will confine magnetic field which is likely your problem.

Magnetic field is produced by moving electrons. When you turn on a heavy draw current like the landing light it draws a lot of electrons which produces a large magnetic field which swings your compass.

The magnetic field effect decreases as 1/(r^2) which means that if you double the distance between the wire and the compass you will decrease the field strength by a factor of 4X.

Move the wires of move the compass or both.

Duane Wilson

Compass problem

I have the same problem, apparently all the Van's guages have a little magnet in them to swing the needles. So, I picked the instrument that should move the least when powered up (the Voltmeter) and put may compass next to that. I plan to calibrate my compass with power on and I should have a constant disturbance next to my compass instead of a variable one (like a tach or mp or fuel guage).

While we are on the subject

I have the Van's MP guage and I have noticed that when I key the mic, the MP guage reacts either up or down depending on which frequency I am transmitting on! Has anyone else seen this/have a solution? I called Van's and they confirmed that their airplanes do the same thing, they said they just ignore it.

Dayton Murdock said:

Hi Dan

I explained my compass deviation problem to the electronic engineer at work. He advised me to wrap all the power wires with aluminum tape and ground one end of the tape. He is confident that any magnetic field generated by power in the wires will be shielded by the tape. I will post photos and the results later this week.

Click to expand...

Dayton,
Your problem is caused by the magnetic field created when current flows through a conductor and aluminum tape won't shield that.
If moving the compass is your least favorite recourse, you need to look closely at the spatial relationship of the high current wires and your compass.
If you can cleverly pair two wires with equal current going in opposite directions, the fields will cancel.
Perhaps you can change the harness to have the wires be perpendicular to their present orientation wherever they are close to the compass.
There will exist a wiring orientation where the net magnetic field created by current flow will be close to zero at the compass.
Think out of the box a little and perhaps add a useless loop of wire behind the panel that does nothing but reorient the field such that the compass deflection is minimized when your big loads are energized.

-Mike

In my situation, I moved the compass around by switching with other instruments of the same size. I had to move things around 2 or 3 times to get it far enough away from the magnetic interference but I got it into an acceptable range.
If you can't get it corrected to your satisfaction, you may want to look at a remote sensing compass. (I believe there is a reg that says you can't have more than + or - 10 degrees error, but you'd have to check on that.)
Also, make sure you swing the compass while everything is turned on, as if you were in flight.