Re: A54 bow thruster directly to battery or through main switches?

James Alton


   No problem at all, thanks for taking the time to help answer my question about the service disconnect switch on your A54. As you correctly point out my bow thruster is a 12V model so the amp draw at the same power is 2X.  I believe my bow thruster motor is only about 4.2KW so the amp draw should be similar to yours.  I am bringing a Fluke clamp meter to my boat this winter to see if I can better pin down the draw.  I sent an email to the manufacturer of the switch to see if they felt that it would work in my application.  I want to be sure that the switch would open in an emergency if there were a short in the bow thruster circuit.  I like the wide separation of the contacts of this switch which makes me think that this switch might work in such an emergency so long as the contacts did not weld together!  


SV Sueno
Maramu #220

I believe that this is the original engine service disconnect switch for my Maramu so 32 years old.  This is how the contacts looked before I cleaned them up.   If you look carefully at the center of the left hand portion of the switch, there is  a hole/bearing that the shaft inserts into a hole.  This is where  the Phenolic had cracks.  This caused the shaft to not center correctly so the contacts probably were not mating perfectly.  This could explain the reason that "exercising" the switch can sometimes restore function. The problem in my case was apparently this mechanical issue in the switch rather than being corrosion or burning of the contact surfaces which has been the case on almost every other switch failure I have investigated.  To open the switch, I just had to carefully open the tabs that were pressed in on each side.  


On Feb 8, 2020, at 8:36 AM, Arno Luijten <arno.luijten@...> wrote:

Hi James,

Sorry to hijack your question directed to Bill. The picture is actually from our boat.
The brand of the switch is the same as yours. However on an 54 we run a 24 volt system so most loads are producing only half the amps compared to a 12 volt system. Not so for the bowthruster, it uses about 8 kW, something like 350-400 amps @ 24v. The main switches can handle that easy as the actual switching never occurs at high amperage.
Thanks for the tip on the mechanical issues you found with the switch. Mine have been suffering from a voltage loss as well occasionally. Until now I was able to resolve this by exercising the switch a few times. 

Arno Luijten
SV Luna?

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