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

[donradcliffe]

+1 on Dockehead's comments. I thought this myth had been busted long ago. I remember a previous thread where I looked up the cranking rating of some deep cycle batteries, and it was equivalent or greater than starting batteries of the same size. Vetus is all wet, as is the OP's electrician.

[Dockhead]

Concerning separate battery banks for bow thrusters:

My boat was actually designed and built with a separate battery bank for windlass, thruster, and (4x) electric winches. This bank consisted of 4x 110AH semi-deep cycle batteries. Then there was the regular domestic bank of another 4x 110AH batteries.

I always hesitate to modify anything on my boat, because she is so much better engineered than anything I could think up myself. But after much thought, and with a lot of wise input from CF'ers, I decided that this was not a good arrangement.

I combined the two banks to make 8x 110AH batteries, for 440AH at 24v.

It works much better. I get double the battery life at anchor. And the thruster and windlass work better because they have double the battery power behind them. Win-win.

I think separate battery banks for thrusters and windlasses is just wrong, UNLESS your thruster is just so far away physically from your domestic batteries that it is impractical to buy cables thick enough to prevent a voltage drop (here, by the way, 24 volts works wonders, compared to 12v).

If you're going to add batteries, add them to your domestic bank. You can, by the way, install a couple batteries in the bow, but just wire them up together with the other batteries so they charge and discharge together. That way you will be using the total battery capacity on board more efficiently. [note added in the cold light of morning: I should not have said "just wire them up". It's not so simple, as another member has correctly pointed out. Read on.]


By the way, my earlier point was not at all that deep cycle batteries are just as good as starting batteries for use with heavy intermittent loads. They are not just as good. But two deep cycle batteries will be just as good for this purpose as one starting battery. And four or six deep cycle batteries will be a lot better. That was my point.

[Dockhead]

An experienced electrical engineer recently started a thread on combining battery banks: http://www.cruisersforum.com/forums/...nks-70865.html

which is relevant to this discussion. He points out that there are a number of dangers in doing this. Worth reading for anyone considering hooking up a couple of bow thruster batteries to the main house bank.

Indeed I should have mentioned, that you should never combine battery banks with different types of batteries (never!), or different ages or conditions of batteries.

AND, you should take great care to make sure that the charging voltage will be the same. If you wire it so that the charging voltage is much lower to part of the bank, that part will never get charged properly and the batteries will slowly die, and then drag down the rest of the bank.

When I combined battery banks on my boat, I consulted with an exerienced marine electrician, who advised me to connect the two banks with a heavy welding wire, to make sure that the heavy intermittent load from the bow thruster (10kW!) would be shared among all the batteries, and would not be concentrated in part of the bank. That's what I did, and it works very well.

Some people think that you should never combine battery banks in different parts of the boat, because of the potential for uneven loading and/or uneven charging. I think this is a minority view, but anyone considering combining battery banks should probably carefully consider the arguments before going ahead.

So -- I probably made it sound too simple -- my bad, and thanks to Flying Cloud for pointing it out. He was too polite to post about it in this thread.

[noelex 77]

I would not change your set up.
There are some cultural differences. Most American boats have their windless / bow thruster powered from the house bank, but European boats are usually the other way around.
Both systems have pros and cons and usually both work well.

[hellosailor]

I wouldn't call Vetus all wet, just bear in mind they are only talking about a THRUSTER not a windlass. The thruster is a perfect "high impulse short duration" load, tailored to an SLI battery. Deep cycle would have no advantage there.

It also wouldn't have any drawback, as long as it was sized adequately to provide the impulse power. I spoke to a couple of battery company engineers (at two out of the three largest in the US) on that point, and they all said very frankly the answer is more in the specific numbers, than the "label" use alone.

When something has been working well for nine years...that's probably an OK way to do it.

[rotorman]

The technicial also recommended to put a condensator between the negative and positive terminals. What do you think about this?

[markpierce]

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.

Question: when are your house batteries ever charged? What you're saying is nonsense to me.

[evm1024]

No Thruster for me but I do have a windlass forward. There is a dedicated starter type battery to power the windlass located forward. I run #8 wire from a breaker connected to the charging bus in the engine room forward to an echo charge regulator that charges the windlass battery. This isolated the loads and allows the windlass battery to charge but not over charge.

I also have a breaker installed that will bypass the echo charge when turned on. The object here is to supply enough current to the windlass (through the #8 wire) to run a nearly unloaded windlass (e.g. lift chain in 20' of water) . should the windlass battery fail. This also can allow the application of more charging current than the echo charge can supply. The breaker will trip when the load on the windlass becomes too great. (or excessive charging current).

Lastly, the windlass battery is a last chance to start the engine should the house and start banks be run flat....

Regards, Ethan

[Roy M]

I prefer using the start bank for my heavy draw applications because, if connected to the house bank, the sudden voltage drop can cause the electronics, on the house bank, to reboot. Plus, the high draw is usually only needed while I operate the engine.

On my circuit breaker panel, my house breakers are white and the high demand loads are red, and draw from the start bank. It reminds me that it might be best to start the engine before energizing the high pressure saltwater washdown pump.

[David M]

On one boat I was on, the bow thruster was connected to the house batteries. Eventually the drain from the house battery bank would cause electronics to kick offline as the house battery voltage dropped, and this of course was with the engines alternator running.

On the other hand connecting the bow thruster to the engines start batteries could drop the engine start battery to a low enough voltage to where the engine dies, because modern diesels that have computer controls require a battery to operate.

There is no perfect solution. Either way, you have to be careful how much you use the thruster and how much battery capacity the thruster has.

[hellosailor]

"The technicial also recommended to put a condensator between the negative and positive terminals."
If that translates into putting a condensor, better known in the US as a capacitor, between the termainls, find out if the tech also irons his socks. Sounds a bit anal compulsive to me.
A condensor would be installed to prevent or remedy electrical noise problems, as it would clamp some surges produced by the motors and prevent spikes or RFI from getting back into the rest of the system.
It would serve no other purpose, and the batteries located at the far end of the cables would probably clamp spikes just as well. In practical terms? If you haven't had problems...it is a $2-5 part that requires five minutes to install. It could fail--they eventually do in 20 years anyhow--but I'd suspect he's just looking for a way to bill out another half hour in labor for something really not necessary.
This is identical to the aftermarket "noise filters" sold for car stereos and alternators. Sometimes they are needed, most of the time, they are not.

[conachair]

Originally Posted by Seaduction

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.

I think you need to be a bit careful there, when the windlass/thruster is running there will be a hefty voltage drop at bow battery, if you have a big alternator then it's possible it could be trying to shove a load of amps down a cable not designed to take it.

[centralyachts]

What a can of worms! I tell you guys, there's more 'smoke and mirrors' around batteries than anything else on a boat. And there are more pros and cons as to whether you run a thruster off the house, cranking or completely separate bank than a forum can reasonably discuss. It depends on so many variables, including what your expectations are from a thruster...
I have a 50' / 35 ton long keel boat. I have a large 24v thruster running off the MAIN bank of AGM batteries. Note: it is not a house, or cranking bank, but a bloody big bank of batteries (BBBofB). I have a separate dual 12v bank for cranking my genset, and this can be pressed into service in the unlikely event that I run the 24v MAIN bank so low I can't start my Gardner diesel.
But my expectations of the bow thruster are low. It's an 'extra hand' to position the boat when arriving at the slip. I don't try to spin the boat on its own axis under thruster. Most times I don't even need it. But when I do - BOY am I glad I've got it.
It gives my MAIN bank a bit of a workout, but for no more than 20-40 seconds each docking, while my wife runs around with the lines. It uses no more than a handful of Ah which are easily replaced in a few minutes of engine fast idle while we are tying up.
If my boat was 12v I'd simply connect all the batteries together, and really enjoy some grunt.
In short, simply because a battery is 'deep cycle' (i.e. it has rope handles) don't think it won't produce serious current. It will. And to say it could be damaged by a short, heavy discharge is plain wrong. You do need to make sure however that ALL the charge is replaced at some point...

[Bill S]

I have a thruster and windlass on the house bank and have the problem mentioned about rebooting the electronics. Also, the electronics (lots, big load) don't like voltage variations, and often glitch when the freezer goes on. I could not move all the sources of interference to the starting battery. I have thought about having two house banks, one for the electronics and one for everything else, but this is difficult and complex. I looked into UPS type devices. Newmar has some devices, but nothing that works on a sailboat. Their UPS must always be connected to a running engine. I found online a product called Sto-p, but they have been unresponsive about answering questions, which makes me leary. How have others solved this problem?

[hellosailor]

Bill, your reboots could be from two causes, each needs a different solution. If they are rebooting because other "stuff" is drawing too much power and lowering the system voltage, you need to beef up the supply so the voltage does not drop, or move the stuff to an isolated or additional battery to maintain voltage supply. if the displays go blank before the reboot--that's the problem. Could be cables that are too thin, batteries inadequate, corroded wiring...a lot of things contribute to low voltage. A DC voltage booster that converts 10-14 volts to a constant 14.4 volts (or something similar), to power your electronics, is another way to isolate them from voltage drops. Better of course to prevent the drops in the first place if you can, i.e. check all the wiring for problems first.


The other possibility is that the windlass and thruster are putting power spikes into the system. That's outright dangerous, because spikes can and will blow out electronics. You prevent that by putting spike protection/supression on the motors as well as on the bus(es) that feed the electronics.

First you have to figure out which problem you have, or whether you have both. Displays blanking or blinking, would be voltage drop. Spikes are harder to confirm, unless you have something fast reading on board, like an oscilloscope or a very good multimeter.