Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 27-07-2015, 06:32   #16
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Alternator interferes with electronic compass

I have some experimenting to do.

As far as moving the compass, it is already 20' away from the offending alternator. The only high current wires near it come from the alternator 5' away that does not cause any issue.

I thought of another experiment to help pinpoint things - if I recalibrate the compass while it is being effected by the offending alternator, the calibration settings will tell me the magnitude of the magnetic field compensated for and which direction it is from the compass mount. However, it will be a week before I can do that one. In the meantime, I will proceed with some of the other experiments.

Mark
__________________

__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 27-07-2015, 06:53   #17
Registered User
 
jeremiason's Avatar

Join Date: Oct 2010
Location: Punta Gorda, Florida
Boat: Sea Ray 270
Posts: 1,427
Images: 2
Send a message via ICQ to jeremiason Send a message via Yahoo to jeremiason Send a message via Skype™ to jeremiason
Re: Alternator interferes with electronic compass

Quote:
Originally Posted by colemj View Post
I have some experimenting to do.

As far as moving the compass, it is already 20' away from the offending alternator. The only high current wires near it come from the alternator 5' away that does not cause any issue.

I thought of another experiment to help pinpoint things - if I recalibrate the compass while it is being effected by the offending alternator, the calibration settings will tell me the magnitude of the magnetic field compensated for and which direction it is from the compass mount. However, it will be a week before I can do that one. In the meantime, I will proceed with some of the other experiments.

Mark
Mark:

Two things... One did the fluxgate ever work correctly and if it did, what did you change since it started being influenced???

An easy troubleshooting method would be to put a temporary long wire on the compass and move it away from all wires and anything electric... Including the secondary alternator.

Then see if it works... If it doesn't your Fluxgate compass is probably bad, if it does you know you have to move the compass because it is being influenced by something.


Good luck!
__________________

__________________
Tom Jeremiason
Punta Gorda, Florida

jeremiason is offline   Reply With Quote
Old 27-07-2015, 07:31   #18
Registered User
 
Dsanduril's Avatar

Join Date: Aug 2011
Location: South Pacific
Boat: Outremer 50S
Posts: 1,451
Re: Alternator interferes with electronic compass

Where is the engine's ignition/instrument panel in relation to the compass? The field current for the alternator is usually controlled by the key switch, and usually passes through the system mono-polar (no associated ground return). On our boat when this happened the battery cables and main alternator cable were just fine, it was the alternator field current, flowing in a wiring harness near the compass, that was causing the problems.

[Edit] an easy test would be to remove the field wire from the input to the regulator, and then source it from some other location. That way you could run the alternator at power without field current in the normal harness[/edit]
__________________
Dsanduril is offline   Reply With Quote
Old 27-07-2015, 07:33   #19
Registered User

Join Date: May 2010
Location: Elsewhere on the Water
Posts: 571
Re: Alternator interferes with electronic compass

Quote:
Originally Posted by jeremiason View Post
I had a similar problem when I had my C-36...


The fluxgate compass was not located near the alternator, but then I realized that the Battery cables were.


When the batteries were discharged the alternator was kicking out about 75 or 80 amps of charging power it would crate a electronic field around the cables and throw the fluxgate compass off. This only occurred when the batteries were discharged and the alternator was in high output.


I moved the fluxgate compass and had no further problems.
Was the compass near the battery cables? How did moving the compass resolve the issue? Were all DC wires creating sufficient magnetic interference to cause trouble, or only high current conductors?
__________________
St. Elsewhere is offline   Reply With Quote
Old 27-07-2015, 08:20   #20
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Alternator interferes with electronic compass

I just did a test with a HH electronic compass next to the main compass. It also changes its bearing when the alternator is running. So that suggests a true magnetic field is present.

However, I don't know what would be causing this. The only wires that run close by are from the alternator that does not cause any problem.

I have a difficult time believing that the alternator is projecting a strong magnetic field 20' out. It is not possible to move the compass any further away.

I will dig through the conduits and related areas to determine if there is in fact a current-carrying cable related to that alternator. Even if there is, I don't understand why the much closer alternator and its cables are not causing any problem. It can't be just that the other alternator is larger because the problem occurs even when the output is only 10A or so.

The field current is supplied by the voltage regulator mounted near the alternator. The engine panels are at the helm.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 27-07-2015, 08:22   #21
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Re: Alternator interferes with electronic compass

Quote:
Originally Posted by Steve Bean View Post
Re twisted wires: I'm referring to a recommendation I heard years ago to twist the positive and negative wires of a DC circuit around each other to avoid interference with a compass. Does anybody here know if this is valid, or an old wives' tale? Might be easy to construct a test.
It's true, twisting wires in a DC circuit eliminates any magnetic field.

It is more likely that a DC wire which goes from the alternator, near the compass and to a battery is causing the magnetic interference.

If you cannot find a solution you can always go back to the old days where you had a Standard compass and a Steering compass. The Standard compass was put in a place away from stray DC caused magnetic fields affecting deviation. The Standard compass was put in a place where much of the deviation could be zeroed out with magnets. For what could not be zeroed out, a deviation card was created. The steering compass was put at the helm. When you were on the heading that you wanted, you "marked" where that heading was on the steering compass. When you had a large course change (greater than 15 degrees or so) you had to do this procedure again. It did not matter the accuracy of the steering compass this way, as long as the error remained constant, which it did as long as you had no large course changes.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 27-07-2015, 09:49   #22
Registered User

Join Date: Oct 2011
Location: Sequim, WA
Boat: Pacific Seacraft Dana 24
Posts: 165
Re: Alternator interferes with electronic compass

Twisting cable does help nullify induced fields/signals that's why Ethernet cables are rated at twists per foot.
It may be you've lost shielding ground connection on the cable, which bleeds off inductive field. Likewise if cable shield is connected on both ends then the current loop is actually causing a problem rather than preventing it.
__________________
Xthewater is offline   Reply With Quote
Old 27-07-2015, 10:14   #23
Senior Cruiser
 
Rockyscience's Avatar

Cruisers Forum Supporter

Join Date: Jul 2015
Location: IN./TX.
Boat: Custom Roberts 65' Ketch (Sold it)
Posts: 73
Re: Alternator interferes with electronic compass

I think it is magnetic, high current loads can generate large mag. fields.
The easy test is a faraday cage around the fluxgate compass or find a metal box to completely surround it with a hole just big enough to see the readout, if that stops the problem you can have a nice one fitted to it later.
Rocky
__________________
Rockyscience is offline   Reply With Quote
Old 27-07-2015, 10:18   #24
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Alternator interferes with electronic compass

The test with the HH compass does suggest there is a magnetic field interference. While putting the compass in a faraday cage may solve the interference problem, it would defeat the purpose of having a compass at all.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 27-07-2015, 10:38   #25
Registered User
 
Terra Nova's Avatar

Join Date: Apr 2007
Location: Marina del Rey, California
Boat: Freya 39 cutter- Terra Nova
Posts: 3,651
Re: Alternator interferes with electronic compass

Quote:
Originally Posted by Terra Nova View Post
You might try isolating from that alternator output the 12-volt source which powers your autopilot compass.
This.
__________________
1st rule of yachting: When a collision is unavoidable, aim for something cheap.
"whatever spare parts you bring, you'll never need"--goboatingnow
"Id rather drown than have computers take over my life."--d design
Terra Nova is offline   Reply With Quote
Old 27-07-2015, 13:47   #26
Registered User

Join Date: Jul 2015
Location: Ft. Lauderdale, FL
Boat: various over the years
Posts: 53
Re: Alternator interferes with electronic compass

Another experiment: Swap the alternators and regulators between engines and see if the problem moves with the swap.

If so, then replace or rebuild the alternator / regulator pair that is causing the
problem.

If swapping alternators does not move the problem, then investigate the wiring closely. Look for a bad ground somewhere in the 12 v. charging and distribution system in the side causing the problem.
__________________
ex-12m-guy is offline   Reply With Quote
Old 27-07-2015, 15:24   #27
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Alternator interferes with electronic compass

I just powered up the compass (the entire N2K bus actually) from a stand alone battery that was connected to nothing else. The problem still exists.

So it has nothing to do with the power source, and appears to be a magnetic interference. From 20' away.

I will try to move the compass away from it, as well as see what cables could be running near it that I am unaware of.

I'm approaching these experiments by how easy and how much time they take instead of being more methodical because we have several things going on right now.

I will save swapping the alternators to later down on the list because that is much more work. I will investigate the wiring on the problem alternator.

I doubt the compass is bad because it works just fine as long as the alternator on that one engine is not running.

There isn't a need for a "standard/steering compass" because this only happens when we are motoring on that engine, and even when the compass is off from the actual heading, the AP either uses a relative heading or nav data, so the course steered is fine, and we can always choose to use the other engine if it is a problem for some reason and we need to motor.

I appreciate the suggestions and troubleshooting help.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 27-07-2015, 18:45   #28
Registered User
 
Wind River's Avatar

Join Date: Oct 2012
Location: San Diego
Boat: Hudson Force 50 Center Cockpit
Posts: 221
Re: Alternator interferes with electronic compass

Quote:
Originally Posted by jeremiason View Post
I had a similar problem when I had my C-36...


I changed the stock alternator to a high output one.


The fluxgate compass was fine when we left the dock, but if we discharged the batteries, say at anchor, the electronic chart heading would be off as much as 90 degrees.


The fluxgate compass was not located near the alternator, but then I realized that the Battery cables were.


When the batteries were discharged the alternator was kicking out about 75 or 80 amps of charging power it would crate a electronic field around the cables and throw the fluxgate compass off. This only occurred when the batteries were discharged and the alternator was in high output.


I moved the fluxgate compass and had no further problems.
I just installed the Airmar H2183 heading sensor . I noticed a similar problem while I had my boat plugged in to dock power last weekend. While the battery charger was putting out 80 amps or so I noticed my heading, compared to the dock shown on my chart plotter, was off by about 45 degrees. Once the batteries were reaching full charge and the current they were accepting was less than about 10 amps, the heading seemed to be more accurate.

I did try moving the sensor as far away from the charger as the current cable would allow (while there was a heavy charge current) and the discrepancy was far less.

Just to be clear though, I have not done any type of calibration on this sensor yet.

I'm sure this does not help you at all, but it is just another case of interference from a high amperage charging source messing with a heading sensor.
__________________
Wind River is offline   Reply With Quote
Old 04-08-2015, 09:58   #29
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Alternator interferes with electronic compass

Well, that was unexpected.

Problem solved. Short story is a ground loop caused by a vestigial second ground wire running near the compass.

Long story: Outside the engine rooms are power terminal posts that connect to the alternator and run to the house batteries. These exist because the wiring runs in a catamaran are long and complicated, and the posts simplify things a bit.

Also connected to these posts (I will focus on the negative post here) in each engine room are a few other wires, such as the ground to the VSR combiners and a cross-over ground to allow starting the engines from the house battery if a start battery dies.

So, when I connected the new alternator, I connected the negative wire to the negative terminal post with the intent that it would then go directly to the house batteries (which it does).

HOWEVER, although I knew there were also negative cables attached to this post and crossing over to the other hull, what I didn't realize was that one of them was a vestigial wire from the factory that not only crossed to the other hull, but CONTINUED STRAIGHT TO THE HOUSE BANK!

Going through a conduit right by the compass, of course.

I don't know why this wire was originally run this way - it is possible the PO ran it for some reason, or reconfigured it - but the result was that there were now two paths from the alternator negative back to the house, and one of those paths ran by the compass without a corresponding positive wire.

So there was a ground loop next to the compass.

Disconnecting that wire solved the problem.

Thanks for all the help and advice.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 04-08-2015, 19:21   #30
Registered User
 
Snowpetrel's Avatar

Join Date: Jul 2012
Location: Hobart
Boat: Alloy Peterson 40
Posts: 3,071
Re: Alternator interferes with electronic compass

Thanks for the update. Interesting Thread, and a great bit of troubleshooting. A good reminder to keep an eye on your compass error!

Sent from my HTC_0PCV2 using Cruisers Sailing Forum mobile app
__________________

__________________
My Ramblings
Snowpetrel is offline   Reply With Quote
Reply

Tags
alternator, compass

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Garmin Handheld devices - GPS vs. Electronic Compass OldFrog75 Marine Electronics 32 22-06-2015 18:23
Garmin Handheld devices - GPS vs. Electronic Compass OldFrog75 Navigation 0 17-06-2015 08:18
S hemisphere compass to N hemisphere compass blewett_john General Sailing Forum 7 07-11-2013 07:49
NMEA Electronic Compass George64 Marine Electronics 6 13-06-2012 09:39
Compass Deviatrion-Compass Card Paul Bradbury General Sailing Forum 6 05-02-2006 15:34



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 05:04.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.