DC drain by Auto Pilot

[Brutus C Paw]

While they were replacing my 5 water input hoses they unplugged the line that feeds the battery charger. When I went to move the boat the batteries were totally drained and fuses in charger blown. The mechanic's thought is that the auto pilot seems to be drawing DC power all the time as it tries to adjust. Question is it normal for the auto pilot to be live on the battery charger line or should it be on the other line? The boat is 2007 38 Sundancer bought new, so this how it came new.

 

[fwebster]

No, the AP should always be wired thru a switch on the dash where the operator can take it off line quickly. Unless someone has been changing your wiring, I cannot imagine Sea Ray wiring an autopilot hot all the time. There may be 12v at some AP components all the time but when the AP switch is off, no current should flow to the pump, etc. That means if the AP is draining your batteries, you have a short somewhere.

Looking at this another way, when the battery switches are off, you should only have power flowing to the bilge pumps. But, even with a stuck float switch and a bilge pump running all the time, the battery charger should put out enough amps to power it and still maintain the battery charge since it has about a 60A capacity.

Besides, autopilots only move the rudder. If the AP was left on and a heading set, the AP would move the rudder to try to correct the heading. Then the hydraulic system moves the rudder until it stops in a fully deflected position where it can go no further. The AP will fault and turn itself off, but not blow a fuse somewhere ahead of the AP. When you power up the boat the next time, the rudder will still be fully deflected so you can easily see if the AP was left set and on.

I'm thinking your mechanic accidentally shorted the connection on the firewall and blew some fuses, and you got the SODDI response……..some other dude did it.

 

[Brutus C Paw]

When the solenoids are off, all is off. What happened is the battery charger line was unplugged and they left the breakers on. The auto pilot is what they think was drawing power on the DC side. I draw about 4 amps DC when everything is off but solenoids on. The dash switch for the auto pilot is off, but mechanic says the autopilot is still trying to adjust.