Bizzare Problem: Autopilot Only Works when Shore Power Is Plugged In

[sgtPluck]

I have a very strange problem with the auto pilot on my boat: It only works if the shore power cable is plugged in (not very useful as you can imagine.)

If that is not plugged in, then when I flip the pilot switch on on the elecrical panel nothing happens, the LCD doesn't turn on and the wheel mounted motor doesn't do anything.

If I plug in the shore power cable and flip the pilot switch on - the LCD beeps and powers up, and the motor activates for a few seconds on the pedestal. i.e. it seems to be working fine.

In addition, it doesn't matter if there is any power coming through the AC power input. I switched the fuse off on the dock, and the autopilot still works. (Mind you I haven't tried pulling the dock end of the cable out and seeing if it still works.)

I have no idea what is going on here, or why my DC autopilot should have any connection to my AC circuit.

Does anyone have suggestions of what to test to see if I can troubleshoot this strange issue?


Thanks.

p.s. this did work at some point. When I did my sea trial before purchase the auto pilot was working.

[sabray]

what is your battery voltage after not being plugged in ie when the auto pilot doesn't work

[amytom]

could it be hardwired to your charger by mistake?

[Fishspearit]

Originally Posted by sabray

what is your battery voltage after not being plugged in ie when the auto pilot doesn't work

I was thinking the same thing, sounds like a dead battery. Shore power charging the battery to turn on the autopilot.

[James S]

In my short life so far...most of these type of mysteries are related to ground or neutral.....did it work before?

[s/v 'Faith']

Bad DC ground.

I suspect it works with shore power plugged in because the battery charger is bridging across the ground...which probably should not be happening anyway. Start at the battery terminals and work your way back to the bus the autopilot is tied to.

Make sure to clean / lube the connections. Take it down even if it looks ok from the outside.

Good luck.

[sgtPluck]

Thx for the feedback...

The battery is fully charged, and it works even if the shore power is turned off (but plugged in), so it would indeed seem to be related to grounding/neutral.

It did work before, but then I had a windlass installed and am wondering if in the process of that install something went awry.

I don't really know what 'bridging across the ground' means with regard to the battery charger (I have to study my copy of 'Sailboat Electronics Simplified' by Don Casey, I'm a complete novice at electronics.)

I'm guessing if the core problem is grounding, that means that the problem is that the pilot needs to be grounded, and is only grounded when that cable is plugged in?

[Chief Engineer]

AC/DC grounding?????

Sounds like a bad battery

or unit is not grounded properly

who installed your windlass?

Always think of what the situation was before it stopped working....what did you/they do that may have changed things. (another lesson from my
Port Engineer/mentor)

[sgtPluck]

The batteries should be fine as far as I know. They are brand new (May) and according to the monitor are fully charged and putting out good voltage.

Since I last saw the autopilot working the boat was repowered and a windlass was installed. I've emailed the guy who did both for me to see if he has any ideas.

I can see how it would appear to be a grounding issue, but shouldn't the auto pilot function even if it wasn't grounded? (Which I assume means connected to the a grounding bus?)

I'm pretty confused, but I guess I'll just follow the wires and see if anything looks out of the ordinary!

Thanks.

[David M]

Break out the multimeter and trace back to where the autopilots pos and neg wires connect to your DC system. Turn your shore power off and back on as you described. Does the voltage level remain acceptable? Turn off your charger(s) with the shore power still plugged in. Does your autopilot work at all? Keep tracing back until you come across what is causing the difference between working and not working.

[sgtPluck]

Thx,
Will try that.
I neglected to mention that the AC switch is off on the electric panel. So the different scenarios I have discovered are:

1) Shore power plugged in but shore power breaker switched to off at the dock, and AC circuit switched to off on the electrical panel - Autopilot works
2) Same scenario as above, except unplug the boat-end of shore power cable - Autopilot doesn't work

The charger was not on in any situation - there was no AC power coming to the boat.

I will try with the multimeter and see what is happening with the voltage in both of those situations.

[amytom]

If you're somehow grounding the autopilot through the shorepower cable I would also check your zincs and look for corrosion. This might seem odd but also check the ground at your engine block and alternator(s).

Remember that the wire can be physically hooked up but with enough corrosion at the right place you could not have a solid flow of electrons. You could even measure 0 ohms resistance on the ground but when you turn the circuit on the resistance goes up and the apparent voltage supplied to the AP will go down.

[Fishman_Tx]

I think s/v Faith got it...
Yup sounds like a "high joint" but I suspect it's not just the autopilot if it's grounded to the boat system ground. Check the boat main ground bus, it shouldn't be depending on a shore (apparant)ground. Do you ground thru a thruhull? Engine block? What else may be on that "leg" that requires an actual ground (not just neg DC) to function? Does it work properly? Check the boat side ground system and I bet you find a hi-res open(high joint) or WAO (wide @$$ open) to whatever your boat uses for ground when under way......
If you just had a repower, check the gnd tie to the engine block or if it used to be there, is it now?

[sgtPluck]

Originally Posted by Fishman_Tx

Check the boat side ground system and I bet you find a hi-res open(high joint) or WAO (wide @$$ open) to whatever your boat uses for ground when under way.....

I'm a novice here, and am not really sure what I'm looking for. What would a "high joint" look like?

Thanks for the tips. I will be going out to the boat after work today with this page printed out

[Fishman_Tx]

Originally Posted by sgtPluck

I'm a novice here, and am not really sure what I'm looking for. What would a "high joint" look like?

Thanks for the tips. I will be going out to the boat after work today with this page printed out

Hee hee, that's the one hidden in the masthead as opposed to the one hidden in the bilge (low joint?). <===>~~ A joke from my "hippie" days...

Just kidding! A high-joint is slang for "high-resistance open", some continuity/conductivity but not much. Can intermittently be working or not. Mostly due to corrosion or can be due to a bad crimp, solder connection, or dirty connection point (paint under the connector @ the engine block?).