problems with a 5kW thruster

Ian_Edwards

Ian_Edwards

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Hi I have problem with a Lewmar 5kW thruster.
It'll thrust in one direction, but not the other.
When I measure the voltages coming out of the controller in the cockpit I see.

12 volts on both lines when the controller is enabled and when the buttons are pressed, I see 6.3volts on the channel which doesn't work and 4.5 volts on the channel which produces thrust. The voltages are passed to some sort of relay box, which is then connected to a reversing contactor, which switches 12 volts to enable port or starboard thrust.

I've replaced the cockpit control unit, but that doesn't cure the problem.

I looks like there is probably a fault in the relay box, which is completely encapsulated.

Is there anyone out there who understands how these thrusters work and could draw me a circuit diagram (or describe it in words?) with the voltages I'd expect to seem to be a 185TT 12volt?

I've got the installation manual, but that doesn't help.

If I know how the relay box works I could probably knock one using individual relays.

The situation isn't helped by the imminent Easter weekend (difficulty of getting spare) and the position of the bow thruster, which is under the chain locker, in a very tight space with the only access being via a small waterproof hatch.
 
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If you swap the connections from the control box to the relay around, this should help you to identify if the relay box is faulty.
 
Thanks pvb, I hadn't thought of that, it was late last night when I was trying to fix it. I'll try it today.

Thinking about it the encapsulated relay box, is probably just 2 relays which connect the 12 volt supply to the contactors, so it should be easy to wire to 30 amp relays and test the configuration with an old cockpit control box I have before using it in earnest. The clever bit which prevents both sides of the DC motor being enabled at the same time, and limits the amount of time the thruster can be used (to prevent over heating), is in the cockpit control box.
 
Thanks VicS, it's a really useful document, it's not quite the same as the thruster I've got, and looks like it might be for a slightly older version. The 4.5 kW version in the document seems very similar to the one I have which is marketed as 5kW.

I wish I'd had it to hand before I started to fault find!

As pvb suggested, I reversed the wires from the relay box to the contactors, swapping the violet and white wires, and the thruster still only works in one direction, but the opposite direction.

So one half of the relay box is knackered.

I've ordered a new relay box from Aquafax today and they have it in stock, but because of the holiday weekend I won't get until Tuesday.

Thanks to both VicS and pvb for their help, I'd like to think I'd have got there on my own, eventually, but the advice was timely and very useful has no doubt speeded up the fault finding significantly.
 
Hi Simon, I'm going to have a go a fixing the relay box, I now have 2 faulty units!

The problem is that they are both completely encapsulated in a hard resin, essentially the electrical bits are built into a box, and then the box has been filled with resin.

I've been thinking about the best way to excavate the bits out of the resin so that I can identify them, I'm fairly sure it's just 2 relays, but the may be some diodes to suppress the switching spikes.

Anyone got any good ideas good ideas as to how go about it? I don't need to salvage the parts, just identify them.

A hacksaw and a big hammer come to mind.
 
Re: problems with a 5kW thruster - final outcome

Just some feedback,

The problem turned out to be corrosion in the main contactor. This was stopping the motor from receiving power when asked to thrust to port. I took the motor and contactor assembly to a electric motor rewinder in Aberdeen and they found the problem, stripped and cleaned and reassembled the contactor, so it now works perfectly. It cost £50, which I though was very reasonable. So I now have a spare thruster motor in the garage.
 
Re: problems with a 5kW thruster - final outcome

Ian_Edwards said:
Just some feedback,

The problem turned out to be corrosion in the main contactor. This was stopping the motor from receiving power when asked to thrust to port. I took the motor and contactor assembly to a electric motor rewinder in Aberdeen and they found the problem, stripped and cleaned and reassembled the contactor, so it now works perfectly. It cost £50, which I though was very reasonable. So I now have a spare thruster motor in the garage.
Click to expand...
It was more likely to be errosion rather than corrosion? High majority of bow thruster issues are contactor related and should always be the first place to look. :-)
 
Re: problems with a 5kW thruster - final outcome

No it was corrosion, the contactor had got wet, actually immersed in rain water, when the yard which did the maintenance in 2014/15 left both the anchor locker and the waterproof hatch into the bow thruster compartment open and it part filled with rain water.
What initially confused me was that it operated OK for the 2015 season, but I guess that the lack of use over the winter and the fact that it has been soaked and the rust got the better of one half of the reversing contactor, apparently it was seized solid with rust.
 
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