bow thruster motor spontaneous start

moreyak

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An incident of spontaneous starting of the bow thruster electric motor occured while moored at marina almost causing a fire. Heating up of the motor caused melting of battery cables and damage to the motor but did not fused out.
12V bow thruster with touch panel control on deck was factory installed on new sail boat delivered less than a year ago.
What are the possible faults/malfunction that might have led to spontaneous starting of the electric motor? Should such a case be covered under manufacturer's guarantee?
 

bythor

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First of all the thruster must be disconnected from the batteries immediately, and you should get a competent marine electrician on board to see where the problem is, why it ocurred and why the fuse didn't trip if the cables melted - the very purpose of the fuse (if fitted) is to protect the cables.
Then I would worry about warranty, but this will depend on the outcome of the sparky's report.
 

misterg

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Hello - Since there haven't been many replies, I'll chip in my non expert view (I know a little bit about industrial electrics, but not boaty ones):

Bow thruster(BT) motor will be controlled by a pair(?) of high current relays or contactors in the heavy, high current cabling leading from the battery isolator to the BT. These in turn will be controlled by a low current signal from the push buttons.

Possibilities:

1) As already suggested, the push buttons are faulty / wet and sent an erroneous signal to the contactors.

2) Fault in the low current wiring which caused one of the contactors to activate

3) Probably not in this case, but the internal contacts of the contactors can weld together - BT would have activated as soon as isolator was turned on

4) Mechanical activation of contactor - depending on the design, it may be possible to close the contactors by mechanical means, rather than the electrical signal (e.g. by something bashing, or leaning on them).

5) Shorting of contactor terminals / wiring by stray bits of metal - if they are fitted in the anchor locker, it could be the anchor or chain which does this.

6) Shorting/grounding of motor terminals / wiring (comments as above)

You say that the heat from the motor melted the cables - I wouldn't have thought that this should have happened - how long was the motor running for, and how did you stop it? Are you sure the cables didn't rub through and short out somewhere, causing the motor to operate in the process?

Fuse should be sized to protect the wiring, not necessarily the motor which I assume is rated for intermittent use.

There, someone who knows about these things should chip in now.

Andy
 

boatmike

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No problem with that answer at all and no need to be modest.
Firstly the cables from the battery to the thruster needs to be pretty chunky. Even with the motor running continuously they should not get hot.
I would agree that the switching circuit has probably shorted causing the motor to run in the first place but the only consequence of this should be that the boat goes around in circles till the battery goes flat! If the main power cables have got hot this has nothing to do with the switching circuit. The power cables are to damn little enough! The fuse fitted is probably of a quite high rating and correct for the proper cables but if the fuse didn't blow before the cables fried, the cables are too small.
The common reason for this is that the batteries are a long way from the bow thruster. You need to calculate the size of cable relative to its length and it is often a surprise just how big they need to be! Betcha the resistence is too high because they are long cables. Seen it sooo... often!!!
 

halcyon

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But he's tied up in a marina !!
First it's installation, wires should not catch fire, thus wrong fuse for cable and/or load.
What is the control system ? is it mounted at the helm ?
Could be touch pad fault, could be a fault elsewere thats melted a control wire to the bow thruster relay resulting in a short, and running the bow thruster.
Only way is to search the boat for the actual fault, but yes there's an installtion fault.

Brian
 

moreyak

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Thanks all for comments and suggestions.
Just to clarify the circumstances, the boat was tied up in the marina. I came back to the boat and smelled cable burning and saw a lot of smoke. The BT motor was still running. I disconnected the battery (batteries are within 2 ft of the BT motor). Electrician checking it suggested moisture/damp entering the touch panel control (but did not explain how).
 

Sailfree

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Don't get wrapped up trying to investigate it. Make sure boat is safe and go straight back to supplier/installer as not fit for purpose under sale of goods act.
 

boatmike

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Which one of us has a sense of humour deficit??? I know he was tied up in a Marina otherwise he would have suffered the same fate as the ooslum bird.....
And of course sodding wires should not catch fire but if the motor was running and not shorted out and the fuse had not blown it is painfully obvious that the circuitry is too light for the load. Of course the fuse should be sized for the circuitry but if the fuse is (as I suspect) the one suggested by the supplier of the bow thruster the wirings too light innit?
 

halcyon

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A leaking touch pad could give it you, a blob of water bridging two tracks is the same as you pressing a button. We had a similar problem with a joy stick control we did, we had a leak around the joy stick seal when thay were pressure washing the boats. sealed box fills with water causing a short across two tracks, and random operation.
But it does not matter what size cable they used, it should be fused to the cable, not the bow thruster load.
So you have a faulty installation, and possibly a faulty touch pad unit, but make sure they prove the unit is faulty, and you do not have some other problem.

Brian
 

halcyon

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[ QUOTE ]
but the only consequence of this should be that the boat goes around in circles till the battery goes flat!


[/ QUOTE ]

Sorry boatmike, I was just reading your reply, have I miss read it.

Brian
 

bythor

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As I said earlier:
'First of all the thruster must be disconnected from the batteries immediately, and you should get a competent marine electrician on board to see where the problem is, why it ocurred and why the fuse didn't trip if the cables melted - the very purpose of the fuse (if fitted) is to protect the cables.
Then I would worry about warranty, but this will depend on the outcome of the sparky's report.'
 

halcyon

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The chap says he has already done what you suggest, so don't panic.

The BT motor was still running. I disconnected the battery (batteries are within 2 ft of the BT motor). Electrician checking it suggested moisture/damp entering the touch panel control (but did not explain how).

Brian
 

roger

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Just to be pedantic - if the copper of the cable melted then molten copper could well have dripped through the boat bottom. Much more likely is that the insulation melted, burned or smoked. A third possibility is an arc or hot spot at a cable joint. Clearly though a poor installation and design.
 
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