A new house bank

I had mentioned in a previous post our 'ailing house bank'.  While it was accepting and holding a charge just fine, its capacity was down substantially. The house bank on a cruising boat is very important, because when you're not hooked up to shore power it's the house bank that powers everything on the boat.


 I was curious about the age of the batteries.  I had found a cryptic "10-6" written under one of the fill caps.  I theorized that that meant "October 2006".

I then pored through the previous owner's maintenance logs, and I finally found when these batteries had been installed.  It looks like they were installed in April 2005, and, having an 18 month warranty, this would make the "10-6" I saw written on the bottom of the fill cap the end of the warranty period.

For a lead-acid deep cycle battery, 8 years is a pretty phenomenal lifespan.  Normally batteries like this are expected to last 4 to 5 years, but the lifespan of a properly maintained deep cycle battery is more a function of the number of discharge cycles and how deep the discharge cycles have been.

So, this meant that I had one more project to take care of; the replacement of the batteries in our house bank.  Just a little warning.  This will be a long post and a little technical.  Proceed at your own yawn risk...

The batteries in our house bank are Trojan T-105 6 volt golf cart batteries.  This is a commonly used battery in this application, as they provide a good discharge cycle lifespan, good capacity (measured in 'amp-hours' or Ah) and all at a reasonable price.  The T-105 is a fairly atypical deep cycle lead-acid or flooded battery. 

I won't go any further into deep cycle battery theory here.  If you want to know more there is a lot of info to be found on the Internet.  One site I highly recommend is the "Northern Arizona Wind & Sun" site.  Their battery FAQ pretty much covers everything you would want to know about deep cycle batteries and their application.

Our house bank consists of six T-105s, hooked up in a series/parallel configuration, as illustrated in the image below.

6 volt batteries configured as a 12 volt house bank

The way this works is that two 6 volt batteries are hooked in series to increase their voltage to 12 volts.  Then, multiple battery pairs are hooked in parallel to increase their Ah capacity.

The Trojan T-105s are rated for 225 Ah, so this configuration gives us 3x 225 Ah for a total house bank capacity of 675 Ah.  This is the total capacity, but not the usable capacity, as you never want to discharge your deep-cycle batteries deeper than 50%.  Therefore, this house bank has a total capacity of 675 Ah, and a usable capacity of  337.5 Ah.

We have an Ah budget (ie, the amount of power we use) of roughly 100 Ah per day, so this means that, on average, we could run from just our house bank for three days before having to recharge.  One way to extend this even further without having to plug in, or run a generator or main engine for charging, is to have solar and/or wind power as an alternative power source.  Yet another of my future projects that I have on the books is a solar charging system for M/V September Dream.  Not sure when we'll be able to get to that, but I'm hoping for sooner rather than later.  We'll see...

So, enough about the amp-hours, time for the nitty-gritty of swapping these bad boys out.

First off, a bit of a safety warning.  If you are in the least bit nervous about working around electrical systems, or aren't sure about the correct safety procedures, my recommendation is to hire someone competent to do this for you.  I spent the first ten years of my military career working on high power radar systems, with enough voltage and current floating around that making a mistake would mean you'd have a very bad day.  I have a very healthy respect for high voltages and currents, and while a 6 volt deep cycle battery isn't much of a risk from a high voltage point of view, the current that these things can deliver in a short situation will do a very effective job of vaporizing anything metallic in their current path, be that a wristwatch, ring, neck chain, or whatever.  This blog post isn't meant to be a tutorial or a how to, it's just a 'what I did' record.  I'm not responsible for what risk level or mistakes that others make.  (Hopefully that's enough of a disclaimer...)

So, here's the patient that I'm operating on today.

Our 'ailing' house bank

First thing is the prep.  I always like to take lots of pictures and make diagrams of whatever I'm taking apart.  It's nice to put something back together and to not have any parts left over. :-)

Make drawings/diagrams before taking something apart

Safety first, so before doing anything, protective equipment is gathered.

PPE and spill neutralization

Eye protection, safety gloves, and in the case of working with lead-acid batteries, a box of baking soda for neutralizing any acid spill.

I know that these are neither electrical gloves, or acid resistant gloves. They are just so that any residual electrolyte on the batteries doesn't come into contact with bare skin.

The next thing I did was to turn off all power on the boat, both power sources and devices that are using power.  After that I isolated the battery bank so that I could turn everything back on without it affecting my work on the house bank.

House bank isolated from the rest of the boat circuits

After that I removed all of the interconnection cables on the batteries.  As you can tell from the next picture, I like to lay stuff out neatly when I'm doing a disassembly.  It makes it a lot easier when you're putting things back together.

Cables laid out in the same position they were attached

Now came the time for the physical work; removing the batteries from the battery box and hauling them to the car.

I didn't have a lifter for these batteries, so I improvised using my favourite material for situations like this; para cord.

Para-cord lifter

Para-cord lifter does the trick

The house bank battery box, empty

Next the fun of carrying these off of the boat, up the dock and putting them into the car.

Old batteries being taken for 'a drive'...

 I used Total Battery as my source for replacement T-105s.  They have a pretty impressive warehouse in the back of their store, with floor to ceiling shelves full of various types of batteries.  It felt a little like a candy store... :-)

a 'Boat Unit' worth of new batteries

So, after spending a cool 'Boat Unit' [1] I had a car full of shiny new batteries.  Back to the boat, and then reverse the process and hauled them all back onto the boat.  I broke down while at Total Battery and picked up a lifter for the batteries, so no need for the para-cord.

I placed all of the batteries back into the house bank box, being sure to get the batteries in the correct orientation.

The new batteries in place

Before hooking all the cables back up I gave each connection a good cleaning with a brass brush.  Then, it was time to carefully rewire the house bank, using my pictures and diagram as a reference.  Once the wiring was done, but before I hooked the bank up to the boat I did a quick voltage check to make sure everything was wired correctly, and then I turned everything off on the boat before reconnecting the house bank.

The new house bank all hooked up

After the connections were complete it was time to turn everything back on.  The house bank is now back up and running, and will hopefully provide us many years of problem free power.

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[1] - "Boat Unit" - By common boater definition, the word "Boat" is actually an acronym, and stands for "Break Out Another Thousand".  As stuff on a boat usually costs more than the non-marine variety, most boaters count money spent in 'boat units' (also know as 'boat dollars') in a futile attempt to lessen the sense of just how much money we all spend.  So, when a boater spends $2500 for engine work he'll usually say "I just had some engine work done that cost me 2 and a half boat dollars"... :-)