To Which Battery Should the Bow Thruster and Anchor Windlass Be Connected ?

[rotorman]

Hi,

I have my Bow Thruster and Anchor Windlass connected to my 700 Ah house battery bank. An electrician was on board yesterday and told me that this is wrong, they should be connected to my engine battery otherwise I seriously reduce the lifetime of my house batteries.

My bowthruster has a 3kw motor. The windlass is 1.2 kw.

Regards
Geza

[Nusailr]

Originally Posted by rotorman

Hi,

I have my Bow Thruster and Anchor Windlass connected to my 700 Ah house battery bank. An electrician was on board yesterday and told me that this is wrong, they should be connected to my engine battery otherwise I seriously reduce the lifetime of my house batteries.

My bowthruster has a 3kw motor. The windlass is 1.2 kw.

Regards
Geza

When you are using the Bow Thruster or anchoring ;usually your engine is running. Your engine battery is being charged all that time. House batteries are NOT being charged. Configuration matters.

[rotorman]

Ok, to clarify: I have 2 alternators, one for the engine and the other is for the house batteries.
I always use the engine when using the bowthruster.
However if possible I prefer to drop/raise the anchor without the engine. It just feels so good to do it silently only using the sails.

[Blue Stocking]

Originally Posted by rotorman

Ok, to clarify: I have 2 alternators, one for the engine and the other is for the house batteries.
I always use the engine when using the bowthruster.
However if possible I prefer to drop/raise the anchor without the engine. It just feels so good to do it silently only using the sails.

Same here . I love to watch that Amptech kick out 80 amps.

[btrayfors]

The electrician was all wet. There's nothing wrong with using your 700AH house battery bank for the thruster and/or the anchor windlass. Further, if your engine is running then, presumably, the house bank is being charged as well as the start battery....at least that's the setup on most cruising boats, even those with a single alternator.

I, too, like to drop and retrieve the anchor quietly and often do so without the engine running.

It's important, of course, to keep your batteries -- all of them -- as fully charged as practicable.

Bill

[Captain Bill]

Originally Posted by Nusailr

When you are using the Bow Thruster or anchoring ;usually your engine is running. Your engine battery is being charged all that time. House batteries are NOT being charged. Configuration matters.

That's an interesting configuration. My alternators charge the house batteries first. My start batteries don't get any juice until the house batteries exceed 13.2 volts and the combiner connects them together. Since my engines typically start on the first turn or two my start batteries hardly get discharged at all. My windlass runs off the house bank.

[djmarchand]

Well, I disagree with two of the assertions made in this thread.

There will be no harm in drawing 250 amps from a 700 amphour house battery bank for a few minutes to power the bowthruster. A large inverter will do this so why is it a problem to do it for a bowthruster?

House batteries ARE typically charged when the engine is running. Only if you have a simple 1,2,all separation switch and you forget to turn it to all after you start the engine will the house batteries not be charged.

In my mind use the starting battery for only one thing- starting. That is a critical enough service (in terms of current draw and simple reliability) to only depend on it do the one thing it does well- start your engine. A large house battery can easily handle bowthruster or windlass loads.

[thinwater]

I have heard of boats with a separate battery forward, for windlass and bow thruster duty. The logic is reduce cable runs and voltage drop. In that case, I can see using a starting battery, because of the large draw, relative to the battery size.

However, connected to multiple deep cycles, the point is moot.

[Jd1]

The thing that is being ignored so far is that house batteries and starting batteries are not the same. Starting batteries are optimized for high load current. House batteries are optimized for less current but much more total energy withdrawal (deep cycle).
Using the batteries for the service they were designed for will always result in optimum life.

[hellosailor]

Geza, the "engine" battery is normally an SLI (starter-lights-ignition) type which I think would be more likely to be damaged by heavy use of the bow thruster. Just kicking it a times would be similar to just using a starter, but house batteries can also tolerate typical loads like that without any problem.

How you keep each charged and how deeply you cycle them is a somewhat larger issue that should be considered as a whole.

And if your boat is long enough to require a bow thruster, that usually means there is a fairly long cable run from the alternator to the bow thruster, with a large voltage drop in it--or some very expensive cabling.

The windlass is more likely to represent a longer heavier drain on batteries--which should be directed to the house bank, or a dedicated deep cycle, because SLI batteries are very quickly destroyed by deep cycling. Typically, as little as 4-6 100% discharges can permanently destroy an SLI battery.

One alternative to all of that, is to install a dedicated battery forward for the bow thruster and windlass. Cabling issues and voltage drop become less significant, since it can use full battery power "locally". That battery would best be a deep cycle type, to support the windlass.

To get a more objective picture, you'd need to figure out the drain (both impulse and total amphours) from the windlass and thruster. Figure in the cabling issues (are they really adequate?) and voltage loss, then the size and charging patterns for your batteries.

But I suspect that switching those bow loads to the starter battery will NOT improve anything. Except replacement battery sales.

[rotorman]

Thanks so far the comments. To clarify: this is an existing setup. The house batteries are deep cycle batteries. I do have very heavy and expensive lines coming from the house bank to the bow thruster. I have been using the boat like this for 9 years now.

Yes the deep cycle batteries are not designed for high draw. I am running the engine, so some of the 250Amps is coming from the alternator. At least 50As but maybe more (the alternator is 100Amp). I don't know how much exactly.
But the rest have to come from the battery.
Is this draw damaging to the batteries? I would need to check with the supplier I guess. I

Normally I would only use the engine alternator to start the engine, but I would not mind using it for the bow thruster as well.

[dohenyboy]

my vetus bow thruster manual expressly says that deep cycle batteries are not to be used, rather that starter type batteries are appropriate.

[Dockhead]

Originally Posted by rotorman

Thanks so far the comments. To clarify: this is an existing setup. The house batteries are deep cycle batteries. I do have very heavy and expensive lines coming from the house bank to the bow thruster. I have been using the boat like this for 9 years now.

Yes the deep cycle batteries are not designed for high draw. I am running the engine, so some of the 250Amps is coming from the alternator. At least 50As but maybe more (the alternator is 100Amp). I don't know how much exactly.
But the rest have to come from the battery.
Is this draw damaging to the batteries? I would need to check with the supplier I guess. I

Normally I would only use the engine alternator to start the engine, but I would not mind using it for the bow thruster as well.

Yes, but 700 amp/hours of deep cycle batteries in good condition will be just fine with an intermittent 3kW load. How big is your start battery? I bet not more than 110 amp/hours. If you were comparing 110 amp/hours of deep cycle with 110 amp/hours of start battery, your guy might have a point. But 700 amp/hours of deep cycle will handle any type of service, including intermittent heavy loads, much better than 110 amp/hours of starter battery.

I would not worry about it at all. All the more, you seem to have been happy with it for the last 9 years. If it ain't broke . . .

[Noname]

Just as thinwater said, I have read that some install separate batteries in the bow for the windlass/thruster and avoid running the heavy AWG2 or larger cable to the equipment. All that is needed is just 8 or 10 gauge wire from the charger to keep it charged.

[Beausoleil]

Here's one option I hadn't thought of:

If your house and/or starting batteries are wet-cells, then you can get away with installing a dedicated AGM or Gel battery for the windlass up forward. The logic is that AGMs/Gels normally require lower charging voltage than standard wet-cell deep cycle batteries - typically 13.4-13.6V float vs. 13.8V. Size your "charging" cables to give a 0.2-0.4V drop, rather than < 0.1V. Then you can get away with different chemistries in the same battery bank...

Regarding deep-cycle versus starting battery recommendation for the windlass by Vetus: since AGM batteries have a lower internal resistance which allows them to be charged at higher current rates than wet cells, then logic follows that they can also output higher current. Vetus is just covering themselves. I've been using AGM batteries for our windlass and for our engine start batteries for over 4 years and they're still holding up strong.