Death By Bowthruster??

[Questor]

Hi Chaps

Last week during my trip to France, the boat behaved perfectly, with the exception of the bowthruster, which decided to become intermittent and died while mooring up in St. Vaast. Fortunately, "Johnny Flybridge", electronics extraordinaire and total nutter (now totally bald due to shaving accident in Cherbourg!!), was on hand and offered to "have a look".

We discovered that the switch at the helm was working, as the relay could be clearly heard down below.

When we delved further into the bilges and exposed the unit, John took the solenoid / relay unit off and decided all that was needed was to clean the contacts, which he did, and even managed to put it all back together again, and hey presto, it worked.

However, these contacts are about a centimetre square each, and the cables feeding the unit are as thick as my thumbs, and when activated, there is one hell of a "crack" with the associated spark, as contact is made

Surely, given the position of the bowthruster, low down in the bilges, the electrics ought to be properly sealed, just incase any explosive gasses may be lurking around, as they sometimes do.

So just remember, unless yours is different, & I bet it isn't, next time you "hit that switch", it could be the last thing you do.

Ho Hummm

R


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[kimhollamby]

Not a QL by chance?

Just had to rebuild the relay on Calm Voyager's QL600. I was told by one dealer that my diagnosis of bad relay was wrong as they never go wrong and that I should look at battery or connections (had already done that) so went ahead and stripped it down anyway (not easy thanks to silly wiring arrangement).

All relay contacts badly burnt. So filed down as much as possible to good metal, reassemble and it works again, after a fashion.

Knowing it wouldn't however work forever ordered a new one two weeks ago; should be in 24 hours later. In fact still waiting and there are 13 units of that part number on back order apparently. Strange that...given the fact that they don't go wrong!

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[Questor]

Re: Not a QL by chance?

I'm not sure of the type, however, this was the same problem - contacts badly pitted. An emery board took them back to looking like new.

So, they do go wrong, and it always happens when you need them. Strange that, isn't it?

R

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[andyball]

Re: Not a QL by chance?

Do they have a capacitor across the contacts...or an inductor to reduce the initial surge?

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[claudio]

There are surge suppression kits available to minimise contact arcing. If the contacts ar arcing badly when contact is made it is because the contacts are bad. Arc is usually generated when the contacts are seperated (break). This is because of the back emf (technical term) from the bow thruster motor.


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[claudio]

Further to my last email, if you connect a 'varistor' across the motor coil, it will clamp the back e.m.f. and suppress the spark.
Unsuppressed circuits cause huge back e.m.f voltages (thousands of volts) these will damage your sensitive instrumentation, GPS, VHF, Navtex e.t.c.

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