New battery shelf and battery bank upgrade

[Jim Walsh]

Orion now has a three battery system. Orion has always had a two battery bank. Since I have owned her this has consisted of a flooded group 27 starting battery and a flooded group 31 house battery. Since I decided to add refrigeration I thought it prudent to go to a two battery house bank along with a dedicated starter battery.
The best place to add a battery shelf was determined to be in the starboard cockpit locker all the way aft. This was essentially an unused space and the addition of a battery box would not adversely effect the items currently stored there. When my icebox was loaded with 70 pounds of ice I sat on an even keel. With the addition of refrigeration I had a slight list to port. The addition of this battery will cure that.
The new battery shelf was constructed of 3/4” exterior ply (with considerable assistance from a skilled carpenter, thanks Steve) fastened with stainless screws and thickened epoxy, then coated throughout with epoxy. I used a 2 1/2” hole saw to make a vent hole on the low side to ensure any condensation which might form on the hull would not build up in a sealed space. This shelf took a lot of trial and error until it fitted snug against the hull because of the compound curvature of the hull in this area. Once I had it fitted I drew the outline of the shelf on the hull and used 40 grit sanding disks to get the area down to bare fiberglass to ensure a proper bond when it was glassed to the hull.
Since I wanted to be certain that this shelf would never come adrift I had a pro do the fiberglass work. One has to know one’s limitations. I’ll get in there with some fresh bilge paint once winter is over.

[Jim Walsh]

My original intention was to just add a third flooded battery but then I started doing some research, mostly because my batteries were from 2016, and I decided to go with AGM batteries. I found that East Penn makes AGM batteries which they market themselves and they provide AGM’s for several retailers who just put their labels on the East Penn product. Defender had the best price and I was going to wait for their spring sale knowing there would be some discount given. Luckily West Marine had a 20% off sale a couple weeks ago, same East Penn battery as sold by Defender with a different label, so I took advantage of it. I purchased three group 31 AGM’s.
All of my battery cables were original 1984 vintage 4 AWG. I discussed replacing them with my mechanic and he advised going up to 1 AWG. I deferred to the pro and every existing original cable was replaced, and the new cables for the new battery were also fitted.
Orion deserves all this attention, she takes very good care of me and I am honored to return the favor.

[jbenagh]

Nicely done! Fridge will be nice in St George's!

[John Stone]

Excellent Jim. I have just the one AGM and I’ve been happy with it so far. I bet you will be too.

[Keith]

Hi Jim,

Great minds think alike! I'm in the process of modifying my two battery compartment to three. On MOONDANCE the battery compartment in under the bridge deck on the starboard side. You can see in the pics that I'm cutting out the old somewhat rotted plywood and replacing with new. The third battery had to move up a bit due to the curvature of the hull but I offset the higher center of gravity by lowering the other two about an 1 1/2". I tabbed mounting blocks to the hull so that the entire new assembly can be easily screwed in instead of the permanent stapled structure that the factory had. It is all painted now and just has to be screwed together in place. I bought two AGM group 24 batteries in 2013 so they will be on their eight year and still holding up well. At that time I upgraded the cables to 1 AWG, shortened them significantly from what the factory had and added 250 amp fuses very close to the batteries. I also just purchased the third battery at the West Marine 20% off sale as well. The new battery will be the starter and the two old batteries will be the house bank. I will send the final install pics in a few weeks after it warms up a bit and stops snowing.

Keith

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[Jim Walsh]

Nice work. I have a Blue Seas terminal stud fuse block on each battery. After reading Maine Sails article a few years ago I added them. Can’t be too safe with the stuff of which I possess only a rudimentary knowledge. I know only enough about electricity to pay it all due respect.

[Keith]

Thanks Jim,

I just noticed that you have slotted the plywood to run the battery hold down straps through. That is a great idea instead of the screwed down plastic battery hold downs. Looks like I have to cut six new slots in the bottom boards.

Keith

[Jim Walsh]

Thanks Jim,

I just noticed that you have slotted the plywood to run the battery hold down straps through. That is a great idea instead of the screwed down plastic battery hold downs. Looks like I have to cut six new slots in the bottom boards.

Keith

Thanks. Those slots are cut into the cleats, made of decking hardwood, which are screwed and epoxied to the top of the plywood box. Steve Laume came up with this useful feature.

[Walter Hobbs]

Wow Keith, AWG 1

I'm partially rewiring my CD 27 and going from AWG 6 battery cables, to AWG 4. Thought that would be an improvement. Also able to shorten cables, one was 14 feet when 10 will be fine. I guess the fatter and shorter the cable the better. Guess I could have gone to fatter cable.

[Keith]

Hi Walter,

If you do the calculations I think that you will find that 1 AWG is the correct size. My calculation and Jim's mechanic came to the same conclusion. You should also look at adding a fuse either on top of the positive battery terminal like Jim did or as close to the battery as I did. The fuse protects the cable from melting and burning your boat up if there is a short.

Keith

[Steve Laume]

Those Blue Seas terminal fuse holders are great. They protect the entire cable and eliminate one connection. I have always been a bit unsure of how big a fuse should be installed. 250 Amps seems like a big fuse. That may be correct for the wire size. A smaller fuse will never hurt anything but may blow out before it needs to. A fuse that is too big could be a problem. If my memory is correct I am running a 125 amp unit and have never had it blow. I know it would depend on the cable size and I don't remember what mine are.

As far as wire size is concerned, doesn't it depend on what the max draw will be, along with the length of the run? I doubt that Walter's CD-27 will ever be able to draw enough current to overwhelm that number 4 wire. If he were running refrigeration and radar while transmitting on SSB then I am sure he would need bigger wire but he might also want a bigger boat to go along with it.

The wire can't be too big but it can be bigger than it needs to be, Steve.

[Keith]

Hi Steve,

It was 9 years ago that I did the AWG and fuse calculations but I believe the the peak draw comes from the starter and yes the length is part of the AWG equation.

Keith

[Steve Laume]

The starter is always listed as the big draw unless there is a windlass involved. Refrigeration could draw a good bit for a short time much like a microwave but I don't think most of us have those. SSB transmission seems to use a lot of power. Water makers are also a big draw but once again not on my boat. I might have a water pump cycle while I am starting the engine with the LED lights on and the chart plotter with Nav instruments going. So what would be a good amperage figure to use if you are sizing battery cables? I am asking, not only because I am too lazy to figure it out but I really don't know what size my battery cables should be.

I have a pretty simple boat in the grand scheme of things, Steve.

[Keith]

Hi Steve and all,

Here is the article that I used for my cable and fuse size. I got it off of this site years ago. https://www.pbase.com/mainecruising/battery_fusing

I hope the link works if not just cut and paste.

In summary:

8 ft cable run should be 2 AWG, 10' - 1 AWG, 14' 1/0 AWG etc....

8 - 35 HP aux diesel should have a 250 amp fuse minimum

Keith

[Steve Laume]

Okay, I am wrong again. I don't think my memory is serving me well on the fuse size. I know I was debating the proper size and looking at two different sizes when I installed them and bought spares. It may have been a choice between 225 and 250 but now I can't remember at all. I might have to look at up grading my wire size as well.

Maine sail's explanations and documentations are always excellent.

Thanks for bringing this to our attention, Steve.