Bow thruster issue on a Moody

[mariadz]

Hi,

On our Easter weekend sail, we noticed on our return that there was a huge pull from the batteries. We traced this to the bow thruster which needed replacing

Any thoughts welcome.

https://mariadz.com/2019/05/20/diagnosing-the-30a-drain/

 

[RichardS]

30 amps earthing through the sea water to .... somewhere? That sounds highly unlikely.

I understand that you disconnected the negative feed to the bowthruster and the drain continued but there is something not right here.

If it really was a 30A short, then you have not got to the bottom of it, or it wasn't 30A.

Richard

 

[Graham376]

30 amps earthing through the sea water to .... somewhere? That sounds highly unlikely.

I understand that you disconnected the negative feed to the bowthruster and the drain continued but there is something not right here.

If it really was a 30A short, then you have not got to the bottom of it, or it wasn't 30A.

Richard

+1

You can drop the ends of both cables into water and no way would that induce a 30A battery drain. Sounds like you have either a cable fault or battery problem.

 

[mariadz]

Thanks for the advice. We'll keep an eye on it but all the evidence at the moment shows that the problem is fixed. Wiring has been checked too but as you can tell from the picture there were a number of melted wires.

We have two battery monitors working in different ways and batteries were new two years ago and have hardly been used,

 

[Kinsale373]

Its unlikely to have been caused by corroded wires. This would normally result in Higher resistance and lower current and poor or zero performance of the thruster.
A breakdown in the Power line insulation to the Thruster motor and resulting short to ground would normally result in short circuit and a lot more than 30A. and maybe sparks!

It sounds to me like a short in the contacts on the reversing relay. These handle big current. A 12 V 3 Kw thruster draws 250A and contacts can wear.
The gaps between contacts in the relay are tight enough and if you get some metal debris or a build up of conductive sludge lodging between the + Ve supply to the Motor and the -ve of the relay coil then you have a path back to the battery and current will flow. I'd suspect the reversing relay on the old unit.

Kinsale 373

Kinsale 373

 

[pvb]

It sounds to me like a short in the contacts on the reversing relay. These handle big current. A 12 V 3 Kw thruster draws 250A and contacts can wear.
The gaps between contacts in the relay are tight enough and if you get some metal debris or a build up of conductive sludge lodging between the + Ve supply to the Motor and the -ve of the relay coil then you have a path back to the battery and current will flow. I'd suspect the reversing relay on the old unit.

Really?