Bowthruster Wiring Options-Ideas?

[C08]

I have fitted a bow thruster and I am wondering about the charging system options and drawbacks.
The thruster will operate from a dedicated starter battery in the bows. The charging will need to come from the battery compartment area where I have banks of 2 & 3 110AH leisure batteries. I do not fancy fitting heavy duty cables back to the rear of the boat, about 12Mx2 cables on the grounds of cost and the heavy cable routing. I plan to have a twin core charging wire (2.5mm/29A) with an inline 20A fuse and an isolating plug at the battery compartment end. Under way the charging isolator plug will hang over the thruster joystick so the thruster will only normally operate from the starter battery. In the event that the plug is left in the in line fuse fuse should blow and protect the charger wiring.
Battery charging when I am off the boat is wind genny and 2x80w solar panels so the starter battery should always be pretty well fully charged and ready to go. Is there any flaw in what I plan to do or anything better. The thruster battery is over specced for the smallish thruster and being only 1 foot away should not have much voltage drop in the well sized cables.

 

[VicS]

First thoughts were for a "battery to battery" charger, but might be overkill.

How about this Sterling "battery maintainer" https://sterling-power.com/collecti...roducts/battery-to-battery-charger-maintainer

 

[C08]

Thanks Vic but it probably does not need to be so complex-I just planned to put the battery in parallel with the bank of 2. All the same type of sealed LA batteries.

 

[superheat6k]

I would have thought 50mm2 cable would easily suffice for your thruster. We buy tri-rated at 3.30 / m (ex vat) so 24 m is less than £100 and is simple. - City Electrical Factors stock it, but their price is slightly higher. Whereas your method will work you are adding a battery and charger and generally making things a lot more complicated, after all you are only going to use the thruster for a few seconds each time you slip and return to your berth.

 

[VicS]

Thanks Vic but it probably does not need to be so complex-I just planned to put the battery in parallel with the bank of 2. All the same type of sealed LA batteries.

I thought perhaps a single box of tricks that could be installed and left to do the necessary without intervention was preferable to a system that required plugging in and unplugging, with a cable draped over the joystick and fuses to blow if you forgot to unplug the charging lead

Perhaps a switchable circuit breaker would fit the bill. More convenient than plugging in and unplugging a lead , would trip if you forgot to switch off and could be easily reset after tripping.

Eg http://www.12voltplanet.co.uk/waterproof-switchable-panel-mount-circuit-breakers.html
or
http://www.12voltplanet.co.uk/waterproof-switchable-surface-mounted-circuit-breakers.html

 

[Rafiki]

As I understand it you will run the bowthruster from a battery in the bows and the Q really is only about charging that battery. When I had a thruster installed last year I went through the same considerations and was intending to use a run of 25mm cable that was already in place to run the anchor windlass from the leisure batteries near the back of the boat. The boatyard installing the thruster initially agreed , but then changed their minds and said that the charging cable from the alternator and shore power needed to be 50mm in order to ensure the new forward battery was well charged ( the re-cabling also involved running the windlass from the forward battery).
Were the boatyard being unduly cautious, or just wanted to maximise their bill - who knows. What I do know is that the set up has given me no problems and the boat yard electricians would have had a fit if they thought I was trying to charge up a bowthruster battery with a 2.5mm cable.

 

[PaulRainbow]

Is there any flaw in what I plan to do or anything better.

Yes, the voltage drop over 12m or 2.5mm cable will mean that the thruster battery will never get fully charged.

 

[lw395]

Yes, the voltage drop over 12m or 2.5mm cable will mean that the thruster battery will never get fully charged.

Unless the OP is terrible at parking and uses his thruster heavily, the battery is probably at more risk of being overcharged.
Typically it will do something like 100A for a few seconds now and then. That's a few Ah a day?
If the main batteries are being held at 14.4v in bulk charging, you can do the math to see if those few Ah make it back.

Where this all can go wrong is if there is an anchor windlass. Normally people use these as sparingly as bow thrusters.
But what if your yacht is being used as a committee boat for a race week? Suddenly it's getting anchored in deeper water three times a day with not much motoring in between!
Such is the danger of making assumptions about how other people use their boats. Maybe the OP is running some sort of ferry service and will do lots of coming alongside with his thruster....

 

[PaulRainbow]

Unless the OP is terrible at parking and uses his thruster heavily, the battery is probably at more risk of being overcharged.
Typically it will do something like 100A for a few seconds now and then. That's a few Ah a day?
If the main batteries are being held at 14.4v in bulk charging, you can do the math to see if those few Ah make it back.

Where this all can go wrong is if there is an anchor windlass. Normally people use these as sparingly as bow thrusters.
But what if your yacht is being used as a committee boat for a race week? Suddenly it's getting anchored in deeper water three times a day with not much motoring in between!
Such is the danger of making assumptions about how other people use their boats. Maybe the OP is running some sort of ferry service and will do lots of coming alongside with his thruster....

More nonsense. Do the calcs for voltage drop over 12m of 2.5mm cable. Baring in mind his charging system will mostly be maintaining float voltage of around 13.4 volts, his thruster battery will not get fully charged.

 

[C08]

I thought perhaps a single box of tricks that could be installed and left to do the necessary without intervention was preferable to a system that required plugging in and unplugging, with a cable draped over the joystick and fuses to blow if you forgot to unplug the charging lead

Perhaps a switchable circuit breaker would fit the bill. More convenient than plugging in and unplugging a lead , would trip if you forgot to switch off and could be easily reset after tripping.

Eg http://www.12voltplanet.co.uk/waterproof-switchable-panel-mount-circuit-breakers.html
or
http://www.12voltplanet.co.uk/waterproof-switchable-surface-mounted-circuit-breakers.html

That is a good suggestion-I could have the break switch by the thruster control. I will try that and keep a close watch on thruster battery voltages (thanks PR) when "fully" charged.

 

[lw395]

More nonsense. Do the calcs for voltage drop over 12m of 2.5mm cable. Baring in mind his charging system will mostly be maintaining float voltage of around 13.4 volts, his thruster battery will not get fully charged.

In practice, a lot of yacht systems spend an awful lot of their time over 14V as the chargers respond to various loads during the day.
The resistance is only about 180mOhm.
From there you have to guess the hours the main bank is being charged and the exact voltages on the OPs boat.
It's a valid approach to running a thruster or windlass.
But you have to get the details right.
And it might be smart to monitor the bow battery volts.
Your calling 'nonsense' to everything that needs more than a cse grade 5 to understand is becoming tiresome.

 

[PaulRainbow]

Your calling 'nonsense' to everything that needs more than a cse grade 5 to understand is becoming tiresome.

As is the drivel you post, most of which makes no sense.

Anyone professionally fitting a windlass would laugh at the idea of running 12 metres of 2.5mm cable to charge the battery up. With just 20a coming from the engine alternator the voltage drop would literally be around 10 times the acceptable maximum.

The windgen or solar panels will not spend most of their time over 14 volts, but even if they did, with a relatively low amp output, the voltage drop is still significant, at just 5a it is triple what would be generally acceptable.

Calling this a " a valid approach to running a thruster or windlass." is pure nonsense.

 

[VicS]

As is the drivel you post, most of which makes no sense.

Anyone professionally fitting a windlass would laugh at the idea of running 12 metres of 2.5mm cable to charge the battery up. With just 20a coming from the engine alternator the voltage drop would literally be around 10 times the acceptable maximum.

The windgen or solar panels will not spend most of their time over 14 volts, but even if they did, with a relatively low amp output, the voltage drop is still significant, at just 5a it is triple what would be generally acceptable.

Calling this a " a valid approach to running a thruster or windlass." is pure nonsense.

What you are overlooking is the fact that the bow thruster battery will not be charging at 20 amps. The OP calls it a "starter battery" which presumably means something around 60 or 70Ah capacity. Although it might initially accept a highish current that will quickly fall to only a few amps.. Such a battery will have a specified bench charging rate of around 4 to 6 amps.

At this much lower current the voltage drop along the cables will be much less. Eventually as the battery charges the current will fall further and so will the voltage drop .

Having said that a few "back of envelope" calculations do suggest that 2.5mm ²/ AWG 14 cable is little on the light side. I'd suggest to the OP that he considers increasing it.


However I do feel that the OP should look again at the idea of the "Battery Maintainer" It really is a simple solution eliminating the Heath Robinson plug in/ out cable draped over the bowthruster control . it is the type of use for which it is intended .

 

[PaulRainbow]

What you are overlooking is the fact that the bow thruster battery will not be charging at 20 amps. The OP calls it a "starter battery" which presumably means something around 60 or 70Ah capacity. Although it might initially accept a highish current that will quickly fall to only a few amps.. Such a battery will have a specified bench charging rate of around 4 to 6 amps.

My thinking was, baring in mind it's connected to the engine battery the alternator would be charging when it was in use, i'd forgotten he plans to disconnect it when using the thruster. But even at 4-6 amps the voltage drop will be significant.

At this much lower current the voltage drop along the cables will be much less. Eventually as the battery charges the current will fall further and so will the voltage drop .

Having said that a few "back of envelope" calculations do suggest that 2.5mm ²/ AWG 14 cable is little on the light side. I'd suggest to the OP that he considers increasing it.

However I do feel that the OP should look again at the idea of the "Battery Maintainer" It really is a simple solution eliminating the Heath Robinson plug in/ out cable draped over the bowthruster control . it is the type of use for which it is intended .

Sterling state "This Maintainer should not be used on a battery with a sustained heavy discharge/drain as it can’t pass high currents." Probably OK most of the time, but a strange marina with a strong cross wind might put a strain on things (extended use of thruster) The cost is approaching that of fitting hefty cables, which would be the most professional approach. They would still need a breaker at the engine battery end and a fuse at the thruster end (or another breaker) but would be getting a charge whilst in use from the alternator, plus a helping hand from the engine battery on difficult days.

 

[lw395]

Personally I would look at not having a bow battery, and spending the dosh on fat cable.
Less weight in the bow and less to go wrong.
Also the alternator will contribute some current.
I appreciate that feeding the cable through the boat may not be a nice job.

I would be slightly concerned about the day in say 5 years time when the bow battery dies of old age.
The first you will know of its reduced capacity might be when you're using the thruster a lot in a crowded marina and a nasty crosswind.

 

[lw395]

What you are overlooking is the fact that the bow thruster battery will not be charging at 20 amps. The OP calls it a "starter battery" which presumably means something around 60 or 70Ah capacity. Although it might initially accept a highish current that will quickly fall to only a few amps.. Such a battery will have a specified bench charging rate of around 4 to 6 amps.

My thinking was, baring in mind it's connected to the engine battery the alternator would be charging when it was in use, i'd forgotten he plans to disconnect it when using the thruster. But even at 4-6 amps the voltage drop will be significant.
.....s.

There won't be 4 to 6 A very often.
The charge required on a typical day is very few Ah. So assuming there is either some solar power or some alternator power for a few hours, the current should be mostly under an amp, dropping to a float current of tens of milliamps.

 

[macd]

Typically it will do something like 100A for a few seconds now and then.

I hope the OP won't be rating his cables and fuses on the basis of that wild guess. Bow thruster motors are typically rated at several kw. (A simple visual comparison with a 'typical' starter motor should tell anyone that.) The OP hasn't indicated the size of his, but it's likely to use a lot more than 100A. Ours, not unusually large, has a specified fuse of 325A.

 

[Lomax]

On second thoughts, I'll stay out of the voltage drop discussion - too many strong opinions

But I will suggest looking at something like the Redarc 1220: https://www.redarc.com.au/smart-start-bcdc Also, whatever you do, always ensure you have a correctly sized (resettable) fuse installed at the supply end...

Edit: Also see http://alfatronix.com/products/view/13

 

[Lomax]

Ok, ok. It must be said. If you intend to power the bow thruster directly from a battery bank which is some 12 metres away from it, you will need to use at least 70mm2 cables. This is assuming that the bow thruster has a power output in the 1-1.5kW range, and thus a current draw of about 100A @ 12V. That would give you a 0.6V voltage drop, which is high, but ok-ish. Can the OP say how powerful the thruster is?

Edit: to put things into perspective, 24 metres of (tinned) 70mm2 cable would set you back about £250.

 

[PaulRainbow]

There won't be 4 to 6 A very often.
The charge required on a typical day is very few Ah. So assuming there is either some solar power or some alternator power for a few hours, the current should be mostly under an amp, dropping to a float current of tens of milliamps.

I give up.