Easy boat electrics question!

[Cardo]

For a change.

Anyhoo, we have a lovely bow thruster on our boat that works very well, thankfully.

However, this is wired up direct to the domestic battery isolator. So, when the domestic batteries are on, the bow thruster has power. Whilst the joystick has a "child safe" mechanism on it to avoid accidental activation, I would rather a proper way to isolate the bow thruster power without turning off the domestic batteries.
Yes, there is a fuse, but it's a faff to get to and I'd rather a more elegant method.
So, I figure a dedicated isolator for the bow thruster should do the trick?

But which one should I get? The fuse is rated at 300A (wowzers!) so needs to be able to cope with that.

 

[MASH]

The joystick is almost certainly only a low current relay switching circuit so it would be easy to fit a switch or even a key switch in the 12v supply to isolate it.

However the thruster itself should (more like must) have some sort of load protection, esp if it is rated as high as 300A. Does it not have one already?
If not there are plenty of windlass isolating switches/circuit breakers available that would do the job.

 

[Cardo]

Plenty of windlass isolating switches/circuit breakers available.

Well, yes, but there seem to be quite a few different types.
Also, should I get something that is also a breaker? My anchor windlass has one of these http://www.marinesuperstore.com/item/2591/ecs-heavy-duty-breaker-100-amp but they only do them up to 150 amp from there.

 

[sailinglegend420]

Wire the new isolator directly to the batteries not via the domestic battery isolator. This almost certainly cannot handle the bowthruster current, and may already have had its contacts burnt. Check the back of the domestic battery isolator to see if the lugs are still at right angles and the case has not started to melt. This is a very common installation error!!!!!

 

[Cardo]

Wire the new isolator directly to the batteries not via the domestic battery isolator. This almost certainly cannot handle the bowthruster current, and may already have had its contacts burnt. Check the back of the domestic battery isolator to see if the lugs are still at right angles and the case has not started to melt. This is a very common installation error!!!!!

The domestic isolator looks fine, but good point anyway. I shall do this, once I have an appropriate isolator!

http://www.force4.co.uk/5800/Sterling-Heavy-Duty-Battery-Isolation-Switch.html
This one is rated at 200A continuous. Not entirely sure how much current the bow thruster actually pulls through, but it's generally not a continuous draw. Would this be suitable?

 

[MASH]

You most certainly need overload protection but as you have a fuse it is covered already. The advantage of a circuit breaker is that if the overload was transient you can reset a cb, but if the fuse pops you have to replace it with the spare which is fine as long as a) it accessible, b) you've actually got one C) you can find it!
Where is the fuse - up fwd or near the battery. It isn't protecting you from damage to potentially vulnerable wiring if it isn't close to the battery.

Wiring it direct sounds very sensible, the domestic battery isolator may well not like that sort of current.

It might be an idea to check the thruster's manual/tech specs to see what amperage it needs to be covered to, people often don't fit the correct fuses and its all to easy to assume that "they must have known".

 

[noelex]

Wire the new isolator directly to the batteries not via the domestic battery isolator. This almost certainly cannot handle the bowthruster current, and may already have had its contacts burnt. Check the back of the domestic battery isolator to see if the lugs are still at right angles and the case has not started to melt. This is a very common installation error!!!!!

The bow thruster needs an isolator. Many battery switches will handle more than 300A continuous.

 

[sailinglegend420]

......Many battery switches will handle more than 300A continuous.

Yes - some will handle 300 amps - but I saw two main domestic battery isolators just last season burnt out by the bowthruster current. Makes sense to wire a bowthruster isolator, and a windlass, and an electric winch direct to the service batteries, via their own isolators.

 

[duncan99210]

The best solution is to isolate the low power circuit - ie the controller. That only needs a standard switch rather than any beefy heavy duty switch. My anchor winch has a permanent supply to the relay box and the control circuits are the ones that are switched at the distribution panel. Also easy to get a locking switch if you'd like to be doubly sure of not activating the thruster by mistake.