Bowthruster battery also engine starter battery?

A

All_at_Sea

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Is this a sensible solution, just run the bowthruster off the engine start one. It will always be being charged when the engine is on which is when will use both the bowthruster and anchor winch - or am I missing something? So long as I re charge the battery by running the engine for a bit after use?
 
Yes that is a sensible solution it just requires fairly stout wiring from engine battery to anchor winch and thruster. ie nearly the length of the boat and heavy enough to not drop too much voltage under load. Winch and thruster can share the wiring however. ol'will
 
It is all about your battery capacity - (Amph) and how much voltage drop you'll get at the terminals near the thruster. You must check your bow thruster specification and see what the rated current is - then apply at least 15% more (that's when protection fuse will kick in and stop the over current). A typical 12V marine battery may be like 100Ah - that's when all the cells function so you assume at least 90% of that - i.e. 90Ah at nominal voltage (12V) which all seems to be fine. BUT If your voltage drops then more current is being sucked out of the battery.

under load condition if you run say 10m 12V cable (low loss) the best you'll get is just above 11V near the terminals in the bow. so that's when the current will increase and not just that by increasing the current the cable will get warmer and more voltage drop will occur to the point that the Thruster's motor won't get the torque and potentially the fuse will pop out...

In most installations you'll see a small motorbike battery near the Thruster to avoid the voltage drop which is also installed parallel to your other 12V battery systems.

remember on average a Thruster needs like 200A or more instantaneous current. (not Ah)
 
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vandy said:
It is all about your battery capacity - (Amph) and how much voltage drop you'll get at the terminals near the thruster. You must check your bow thruster specification and see what the rated current is - then apply at least 15% more (that's when protection fuse will kick in and stop the over current). A typical 12V marine battery may be like 100Ah - that's when all the cells function so you assume at least 90% of that - i.e. 90Ah at nominal voltage (12V) which all seems to be fine. BUT If your voltage drops then more current is being sucked out of the battery.

under load condition if you run say 10m 12V cable (low loss) the best you'll get is just above 11V near the terminals in the bow. so that's when the current will increase and not just that by increasing the current the cable will get warmer and more voltage drop will occur to the point that the Thruster's motor won't get the torque and potentially the fuse will pop out...

In most installations you'll see a small motorbike battery near the Thruster to avoid the voltage drop which is also installed parallel to your other 12V battery systems.

remember on average a Thruster needs like 200A or more instantaneous current. (not Ah)
Click to expand...

Oh dear, not much in there that isn't wrong.
 
All_at_Sea said:
Is this a sensible solution, just run the bowthruster off the engine start one. It will always be being charged when the engine is on which is when will use both the bowthruster and anchor winch - or am I missing something? So long as I re charge the battery by running the engine for a bit after use?
Click to expand...

Yes, that's perfectly OK. You need to use heavy cable, the size of which will be governed by the cable lengths and the current draw of the bow thruster. You then fit an appropriately sized thermal breaker at or very close to the connection to the battery, rated for the bow thruster. If you fit an isolator switch forward, you can connect the cable to that, then take of two outputs. One to the bow thruster and the other to the windlass, but you need to fit another thermal breaker in the windlass positive, close to the isolator. You'll obviously need to connect the negative to a substantial terminal post, taking two negative off for the thruster and windlass. The cables for the windlass can be smaller than those for the thruster.
 
PaulRainbow said:
Yes, that's perfectly OK. You need to use heavy cable, the size of which will be governed by the cable lengths and the current draw of the bow thruster. You then fit an appropriately sized thermal breaker at or very close to the connection to the battery, rated for the bow thruster. If you fit an isolator switch forward, you can connect the cable to that, then take of two outputs. One to the bow thruster and the other to the windlass, but you need to fit another thermal breaker in the windlass positive, close to the isolator. You'll obviously need to connect the negative to a substantial terminal post, taking two negative off for the thruster and windlass. The cables for the windlass can be smaller than those for the thruster.
Click to expand...

Do this installation and it will be an immediate fail if I do the survey for many reasons...to start with the position of thermal breaker!
 
All_at_Sea said:
Is this a sensible solution, just run the bowthruster off the engine start one. It will always be being charged when the engine is on which is when will use both the bowthruster and anchor winch - or am I missing something? So long as I re charge the battery by running the engine for a bit after use?
Click to expand...

One school of thought is that the engine start battery should have absolutely no other role.
This used to be enshrined in the offshore racing regulations, I'm not sure about the current version.

ISTM that the engine will equally charge the house bank when its running and will put the charge back into a bigger bank more quickly.

Practically, if the wiring run is easier to the engine battery, there is a case for doing that.
 
inception said:
Do this installation and it will be an immediate fail if I do the survey for many reasons...to start with the position of thermal breaker!
Click to expand...
Where do you believe the breaker should be, other than close to the power source?
 
vandy said:
Really? Clearly you haven’t done your homework well before you came to the this industry...or is it why so many boats catch fire as they’ve done “bodge job” on wiring...
Click to expand...

I really don't have time to correct the many errors in your post. Your "small motorbike battery" did make me laugh particularly loud though. How does that stop the voltage drop from something that draws 200a (according to your own figures) ?
 
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All_at_Sea said:
Is this a sensible solution, just run the bowthruster off the engine start one. It will always be being charged when the engine is on which is when will use both the bowthruster and anchor winch - or am I missing something? So long as I re charge the battery by running the engine for a bit after use?
Click to expand...

As lw395 has suggested, it would be better to wire it to the domestic bank.
 
All_at_Sea said:
Is this a sensible solution, just run the bowthruster off the engine start one. It will always be being charged when the engine is on which is when will use both the bowthruster and anchor winch - or am I missing something? So long as I re charge the battery by running the engine for a bit after use?
Click to expand...
How big is the boat?
 
Dependent upon your charging system, it might be better off your engine battery. When I fitted a BEP VSR the recommendation was to run such heavy loads from start battery rather than house. Either way, although a local battery is better overall subject to a suitable charging system, running from the start or house batteries is quite common in my experience but usually requires heavy gauge feed cables.
 
inception said:
Do this installation and it will be an immediate fail if I do the survey for many reasons...to start with the position of thermal breaker!
Click to expand...

Your profile says that you're a marine engineer, so i'm interested to hear what this "survey" is that you're going to do and how it can "fail". Usual boat survey isn't pass or fail, inland BSS inapplicable, so i wonder what you're referring to.

Perhaps you could also explain why you think my suggestion to be wrong, in particular, where do you think the thermal breakers should be situated ?
 
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