Wiring Size to Forward High Load Battery ?

[SvenG]

I've capitulated and admit that a manual windlass is not the ideal solution for our all-chain road and beefy anchor when anticipating frequent anchoring.

Once I admitted defeat I also admitted that we'd most likely want to have a dedicated forward battery to power the windlass (and salt water wash-down ?).

Assume the windlass draws 80 Amps and will use about 5 minutes of that current for a full retrieval, that's under 7 Ah. So let's say I put in a 100 Ah gel to handle the load.

Would that setup let me essentially trickle charge the windlass battery between windlass uses ? Would there be enough of a temporary voltage drop at the battery to try to pull enough current through the "trickle-charge" wires to cause a problem ? Specifically, would the "trickle-charge" wires have to be so beefy that I might as well just run direct wires from the house bank to the windlass ?

Thanks,



-Sven

[David M]

Don't worry about it too much. The anchor battery will not draw more current from the house batteries than what the wires can handle causing the wires to heat up above what is safe. What will happen is as the current increases so will the resistance which will put a limit on the amount of current that can flow through the wire. There will not be a large enough potential difference between the two batteries for there to be a concern. This does not mean you should run 18 gauge wire though. Depending on the run, I think in your situation something like 8-10 AWG would work good enough.

Of course, the larger the gauge of wire you install between your house bank and your anchor windlass battery, the quicker your windlass battery will recharge.

How long is your run? For an 80 amp load, it may not be worth it to have the battery at all. The battery may end up costing more than the larger gauge wire and the amount of time you have to put into the project including creating a place to mount the battery. You also have to consider the future cost of changing out this battery roughly every five years.

[cal40john]

What do you mean trickle charge? Do you have a device that puts out limited current?

Determine max current from your source, determine whether you want 3% or 10% max drop, look at table for wire size. Check ampacity table to make sure that the wire isn't too small for the current.

Tables and description here:

BoatUS BoatTECH Guides: Choosing Cables & Terminals for Marine Service

[SvenG]

Originally Posted by David M

Don't worry about it.

<snip>

Of course, the larger the gauge of wire you install between your house bank and your anchor windlass battery, the quicker your windlass battery will recharge.

That's kind of what I expected and hoped someone credible would say.

Appreciate the quick answer.

Yes, I am open to conflicting opinions but think David probably gave the needed answer.




-Sven

[David M]

You were too quick Sven. I added more to my original post.

What is the run from the source to the load and back? I'm thinking you may not need a battery because the battery may end up costing you more than the cost of larger gauge wire. It all depends on the run.

[DeepFrz]

Just make sure that you fuse the wires at both ends, close to the batteries.

[cal40john]

If you go with the battery in the bow route. I assume you're not going to hardwire the windlass battery to your house bank permanently. Though you probably intend to cross connect the banks and have the engine running while raising anchor, say you have a problem or an accident that discharges the windlass battery half way. A flooded cell 100 AH battery will accept around 30 amps with a charge voltage of 14.4 volts at half charge according to the graph in Calder's book. A 60' round trip with #8 wire is a 10% drop in voltage, and the ampacity is 80 amps. So David's wire size works out fine for that. An AGM probably has a higher acceptance rate, or a higher charge voltage means more current also, so you could have a larger voltage drop.

How did you determine that you were only trickle charging the battery?

An Echo Charger would limit you to 15 amps.

[svHyLyte]

Sven--

I went through the same deliberations when we finally added an electric windlass to our boat in 2006. After extnesive research and not a little help from a number of experts on this site (at the time) we ended up running cables from our house bank to the windlass and are glad we did. A part of our experience is detailed at http://www.cruisersforum.com/forums/...bles-3456.html . Photos of our resulting installation and the wiring appear on the second page of that thread beginning at about post #22-#23.

FWIW...

PS: The 39B is a very handsome yacht. Good for you!

[SvenG]

Originally Posted by svHyLyte

A part of our experience is detailed at http://www.cruisersforum.com/forums/...bles-3456.html . Photos of our resulting installation and the wiring appear on the second page of that thread beginning at about post #22-#23.

Nice description. Also a good example of why this forum is so useful !

PS: The 39B is a very handsome yacht. Good for you!

We were very lucky to get her. Lew (the PO, who is sometimes here) did a beautiful job replacing the headliner and she appears to have been mostly daysailed the first 30 years.

You have a younger beauty of your own and it looks like you are treating her right too.

Back to the topic, we'll have to consider your solution too. Long high-amp runs scare me but low current small wires can also burn up your boat.

Thanks to all for the inputs so far.



-Sven

[pacific_voyager]

I want to chime in here that IMHO a forward windlass battery is a very bad idea. Much more effective are heavy gauge wires from the main bank. Here is the reasoning:

1. The charging regime for the forward battery will require that it be disconnected from the main bank except when being charged (i.e. voltage over 13.8V). YOU CANNOT WIRE THE FORWARD BATTERY IN PARALLEL WITH THE MAIN BANK AT ALL TIMES or you will ruin both batteries.

2. With a forward battery, the main engine cannot be used to provide additional, backup, or emergency power to the windlass. This is a safety issue. You need that windlass to run.

3. To properly charge the forward battery you won't be "trickle" charging. You will need fairly heavy gauge wires in any event -- why not save the effort of an additional battery.

An anchor battery sounds like a good idea at first; but it isn't. Keeping It Simple is running large cables.

[CDunc]

OK here is another solution to the issue, I assume you have some type of inverter for AC power, run a lead from the AC source to a battery charger forward next to your windlass battery, the size of the AC wire will be minimal saving weight and cost.