USB charger at the helm

[2953]

Small project, but to check first.  I would like to install USB charger at the helm as I use an iPad as repeater for chartplotter at nav station.  I propose directly wired to house battery (fused), tinned wire, etc.  Q: should I be concerned about potential interference with the compass?

[Don Reaves]

When you install the charger, twist the power wires together. This will help eliminate radiated interference from the power supply that would affect the compass.

I have installed several USB chargers on my boat, and they create various amounts of RF interference. While this probably won't affect the compass, it might affect your handheld VHF, if you use one. I would test any proposed charger by temporarily wiring it up and plugging in a device to charge. See whether you can pick it up interference on a radio. An AM radio is best for this test.

[2953]

Thanks for the reply.

[tsenator]

Jan 30, 2024 11:46:37 GMT 2953 said:

Small project, but to check first.  I would like to install USB charger at the helm as I use an iPad as repeater for chartplotter at nav station.  I propose directly wired to house battery (fused), tinned wire, etc.  Q: should I be concerned about potential interference with the compass?

I’ve never worried about it affecting the compass, but if you are concerned you can tell how much it might affect the compass by connecting a large load in the charger and turn it on and off and seeing if the compass moves.  The more correct through the 12v wires for the test the better. 

[seattledale]

I agree with twisting the power wires of the charger feed wires in the vicinity of the compass.  Current passing through a conductor (wire) will create a magnetic field around the wire.  The polarity of the magnetic field will be of one polarity when the current is passing "left to right", and of the opposite polarity when passing "right to left".  The positive wire has current in one direction and the negative wire has current in the opposite direction.  By twisting the positive and negative wires together the magnetic fields will cancel each other out.  Generally two or three twists per inch should work fine for cancellation, although I'd probably try not to have the twisted wires laying right across the compass.  The USB charger could also create a bit of RF interference due to the switching power supply and regulator inherent in USB devices.  But unless you are using a fancy electronic compass I doubt it would be of much consequence. 

As the other posters suggest, best test is to power it up while watching the compass.  If it doesn't move then you're good to go.

[moonshadow]

Also I suggest testing to make sure it doesn’t interfere with your GPS antenna reception. These receive really weak signals and amplify whatever the see quite a bit. I learned the hard way.