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Old 10-09-2013, 21:16   #1
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analog meters vs compass

Hi:

Sometimes one gets so focused one one thing, one forgets what every 10 year old knows ... keep magnets away from the compass.

For the sandpiper 565 I made two really nice hinged panels with a battery switch, 6 switches and fuse holders each side, a volt meter, and a 1 mA meter installed for future usage as a battery current meter when I made or otherwise sourced a suitable shunt. I had all the nice parts in stock because I was buying for the Ontario 32, so proper marine wire, heat shrink ring terminals, the whole nine yards. It was beautiful.

Then one day in the driveway with the boat pointing pretty much north, I noticed the compass said east! It dawned on me what was likely the problem. I did some quick research and realized that much error wasn't going to be compensated away.

I now have two large holes, and a few smaller holes that are now assigned to be a very custom grandson photograph mounting system.

I'd still like a voltmeter some day, but I'll have to mount it elsewhere, and I am not sure where the elsewhere will be on an 18 foot boat.

After I dug the meters out, I performed some tests. The meter began swinging the compass at about 18 inches of separation. I originally had the two meters mounted at about 10 inches of separation.

I now quote Mr. Simpson: "D'oh"

Cheers

Boulter
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Old 11-09-2013, 08:00   #2
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Re: analog meters vs compass

Hmm... are these moving iron meters or moving coil meters?

I would not expect the average moving coil meter to have that much effect on a compass. If they are moving iron, try a moving coil and see how it goes!
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Old 11-09-2013, 08:12   #3
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Re: analog meters vs compass

Electrical equipment of various types affect the sensitive compass movement. I had to relocated a compass after installing a chart plotter because of the magnetic interference.
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Old 11-09-2013, 08:28   #4
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Re: analog meters vs compass

G'Day Boulter,

There are a few possibilities for alleviation of your problem. As Geoff says, some analog meters have much less external mag field than others. Or you could use digital meters, or finally you could search out some Mu-metal or other high permeability thin sheet metal and construct a shield around the existing meters. Here's a link to one supplier of such materials:Magnetic Field Shielding Materials - EMF Safety Superstore.

Good luck

Jim

Hmmm... doesn't look like the link happened... try googling Mu-metal and you will get several sources.
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Old 11-09-2013, 09:07   #5
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Wiring usually has way more impact on a compass than devices. Always check the wires before suspecting the device itself. Wires anywhere near a compass should have + & - twisted together to minimize stray magnetic fields. I would bet at least one beer that when a chart plotter or amp meter affects a compass it's the wiring that's really at fault.
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Old 11-09-2013, 09:21   #6
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Re: analog meters vs compass

Quote:
Originally Posted by transmitterdan View Post
Wiring usually has way more impact on a compass than devices. Always check the wires before suspecting the device itself. Wires anywhere near a compass should have + & - twisted together to minimize stray magnetic fields. I would bet at least one beer that when a chart plotter or amp meter affects a compass it's the wiring that's really at fault.
The implication of the OP was (boat on trailer in driveway) that there was no current flow involved, and hence the wiring (or current flow within it) is not the source of the deviation noted.

Cheers,

Jim
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Old 11-09-2013, 20:05   #7
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Re: analog meters vs compass

Quote:
Originally Posted by Jim Cate View Post
There are a few possibilities for alleviation of your problem.
Thanks for the ideas Jim.

Boulter
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Old 18-09-2013, 09:37   #8
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Re: analog meters vs compass

Quote:
Originally Posted by Jim Cate View Post
Or you could use digital meters,
Here's one

M451 Digital Voltmeter | Davtron Inc

I haven't tried it.

Good luck
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