Autopilot affected by starting generator?

[Capt. Rodbone]

When underway and my bride driving when I go below and start the generator she says the auto polite alters course every time. First thought was “how”, since Autopilot is DC, but then realized once I flip the breaker the generator is producing power to the DC system.

Do any or you experience the same?

 

[Gdavid]

I've never experienced that, but it could be a drop in DC voltage while the starter is engaged if it is on the same battery bank as the electronics or it could be an induced magnetic field caused by high current interfering with your autopilot's compass. Either would be pretty easy to fix.

 

[DavidM]

Does it only happen momentarily when the engine starts.if so, it may cause a short term voltage drop that may affect the autopilot, but maybe something else:

The fluxgate compass used in most autopilots is sensitive to small magnetic fields caused by current flowing in a nearby DC conductor. Find your fluxgate and look for any DC conductors nearby like engine starting circuits. AC conductors shouldn’t affect fluxgates significantly.

David

 

[Bmarler]

My autopilot compass is mounted too close to the wiring for the lights in the head. Every time someone turns on the lights I go 10 degrees to port.
I’m going to remount the compass sometime.

 

[sunchaser]

On occasion starting our microwave affects the AP.. This occurs with genset off but an obvious short term high power draw through the inverter. So when microwave turned on the helms persons gets alerted.

The install off our ACR seems to have reduced this “non issue” happening and likely a DC to DC would do the same for us. Boat electrics are weird

 

[tiltrider1]

If it’s a temporary course change then it’s a low voltage drop. You can either ignore it or move the autopilot’s power source do a different battery bank.

If it is a permanent course change then you can either ignore it and alter course by 10 degrees or relocate the fluxgate compass away from the generator’s magnetic field.

 

[tiltrider1]

Speaking of strange autopilot behaviors.

Boat A, autopilot worked perfectly except when boat crossed a Bayliner 4585 wake, then it went crazy. Discovered FC was located close to a magnet but only the Bayliner wakes were steep enough to cause the issue.

Boat B, autopilot worked perfectly except when “American Woman” was played on the stereo. Turned out any heavy base song with lots of volume created the problem but customer only cranked up “American Woman”

Boat C, autopilot worked perfectly most the time but would do random 360’s at random times. We never coUld duplicate the issue but did experience. Changed the FC and issue went away.

Boat D, autopilot worked perfectly most of the time but would occasionally take 90 degree turns. Discovered that we could duplicate this by turning the refrigerator on and off. Relocated the FC and problem was solved.

 

[Gdavid]

Reminds me of Cousin Eddie, "Every time Catherine revved up the microwave, I'd piss my pants and forget who I was for about half an hour or so."

 

[Circumnavigator]

Back before Fintry had a satellite compass, when we were crossing the Ted Williams Tunnel in Boston Harbor, the boat would go 20 degrees to the right. There's a lot of steel in the tunnel, even though it's 40-50 feet down.


The same thing happened going through bridges. Since Fintry is fairly hard to hand steer and the current through bridges is often gnarly, that was a principal reason for the satellite compass. The other major advantage is that COG stays stable even if the boat is rolling.


Jim

 

[Hippocampus]

Distance and ferrites are your friends


Had trouble when I transmitted on the SSB stuff would screw up.

 

[diver dave]

Distance and ferrites are your friends


Had trouble when I transmitted on the SSB stuff would screw up.

True for much EMC, but ferrites won't absorb 0MHz fields.

My SSB turns on the AIS system; until I added mix 31 ferrite to the AIS power cable.

 

[TowLou]

Could have your battery wires close to the compass altering the magnetic field around it. Ever see a wire jump up from current flowing through it?

 

[BobMc]

When underway and my bride driving when I go below and start the generator she says the auto polite alters course every time. First thought was “how”, since Autopilot is DC, but then realized once I flip the breaker the generator is producing power to the DC system.

Do any or you experience the same?

Had similar experience on Sanderling. Every time the fresh water was turned on (and the water pump operated) the auto pilot would deviate from the heading it was on; this was the result of a lot of head-scratching over a number of months trying to pinpoint the culprit. The fluxgate compass was mounted too close to the water pump (about 2.5 feet away) and there was no way to move either. I built a Farraday cage using 1/2 inch heavy wire screening around the water pump and grounded it to the boat's ground. That eliminated the problem.

Better solution came a few years later when we installed a new autopilot system (Simrad) with a Precision-9 solid-state compass.

 

[High Wire]

You don’t necessarily need to move the compass to deal with strong magnetic influence of DC electric currents. If you twist the positive and negative leads into an easy spiral, the magnetic effects will cancel each other.