Charging 4th Battery

[mrplastic]

Hi all,

I will shortly be running the cables to my new bowthruster. The question I have regards charging via the engine. The battery ( a 100ah gel) is about a foot from the thruster motor and I'll be running a couple of 16mm cables around 8 metres in length to the battery for charging.

The current set up is 1 engine battery, 1 domestic battery and another for the windlass. The latter two are wired in parallel and charged together with the engine battery via a split diode relay.

Can I remove the existing 2 battery split diode and simply replace it with a 3 battery unit and run my charging cable from there or is more complicated than that?

As always, useful advice is much appreciated!

 

[bobgosling]

Have you looked at Sterling's "Battery to Battery" charger which is designed for this very problem. I think you will have problems with voltage drop over a diode + long cable unless you are using an intelligent charge controller.

 

[mrplastic]

Well that's a first class reply! I've just checked out their website and they have installation diagrams showing precisely the system I currently have and how to modify it!

I will order one today! Please accept 5 gold stars and my thanks!

Cheers

 

[andy_wilson]

A windlass presents all the same problems as a bow thruster, so where is the windlass battery, and how is it charged?

Surely a smart solution would be to spec. the battery for the bigger of the two loads, and have one battery up front to feed both motors. Saves time (installation), money, and probably the biggest concern would be reducing weight right at the pointy end. Sounds like you already have cables running to the front. You could consider two charging scenarios.

1. These items are considered domestic loads and are split charged from the domestic battery.

2. These items are always (or largely itended to be) used when the engine is on, and therefore are split charged from the engine starting bank.
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There, managed to avoid asking why you feel you needed a bow thruster on a Beneteau 311 Oceanis.

Oops, just did!

 

[mrplastic]

The windlass battery is just in front of the engine so your wrong in your assumption of it's location.

Why do I want a bowthruster on a 311....Have you tried manouvouring one in a busy Marina...........thought not otherwise you wouldn't have made the point would you?

It has twin rudders so no propwash and it also has a healthy kick to port....you stop this boat in a crowded marina and it's very difficult if not impossible to move it around purposely and with any accuracy.

And anyway why not? Boating to me is about enjoyment and relaxation, I don't enjoy the stress of difficult berthing at the end of a relaxing day.....I'm sure you'd feel differently if you were in the adjacent berth.........

And yes, I'm sure there are sailing purists out there who would ask you why you have an engine?

 

[andy_wilson]

Wrong assumption?

"so where is the windlass battery, and how is it charged?"

I actually assumed it was not at the front given your description of the cables you have running up the front, but I didn't let my correct assumption get in the way of clarifying!

If it was mine, and a fresh intallation I would have one battery for both puposes, at the front with split charging from the engine side via smaller, fused cabling. This is what I would consider an optimum installation.

You already have heavy cabling, and are highly unlikely to use both bow thruster and windlass together (which you could prevent if you wish via a suitably designed changeover switch).

A good solution (no assumptions, will the existing battery spec. be good enough for either windlass or thruster?), would be to terminate existing heavy cables with a split to two relays with contacts suitable for the respective loads, each to supply thruster / windlass. Activate relays from the helm with a 3 position Thruster / Off / Windlass switch.

You could use the existing split charge system 'as is' for this battery, but if not already arranged as such, split from the engine battery charging makes most sense, for reasons previously given.

Finally however, it sounds as though you are already about to fit a battery forward anyway. If so, I would still look for one battery to cover both duties up front. You could leave the existing split charger and cables to feed the for'ard battery. With separate cables from the battery to each motor, no need for complex changeover switches and relays beyond the standard controls.

The now unused windlass battery aft could then be paralleled to the domestic bank to increase capacity, which is never a bad thing IMHO.

Battery to battery chargers are great for this purpose, but I wonder if you need to sink another couple of hundred quid (by the time it is fitted, cabled and terminated etc.) into this project? Then again, why not!

BTW, you assumed right, I have never had to get a 311 Oceanis with twin rudders and a port hand kick, in or out of a tight berth. I have had the dubious pleasure of 'shifting' just about every other kind of craft, large, small, sail, power, deep underwater, big windage, single, twin, shaft, outdrive, with / without bow thrusters, wind or current from any direction blah blah blah.

On occasions one gets it completely wrong. Sometimes you see what might go wrong and you have an escape plan which may be little more than a well placed crew member with a loose fender. Sometimes the berthing can change from impossibly difficult if you go straight in NOW, to easy if you pick up a mooring, have a brew and pack away, then slide in smoothly when the tide has turned in 2 hours, ready to step straight ashore and pack the car.

Just a question of approach, and attitude. And we are both entitled to our own.

Hope my comments on your electics are of some help.