Battery Replacment advice

[chucklesR]

Sorry, no snidness intended - not in my character or intent.

ABYC standards don't specify, but I will however point out that such switches are intended for single bank installations, not for multiple banks.

Not one manufacture would save a penny by installing two single switches instead of one both - because Murphy's law will come into effect and absolutely ruin your day; 700 miles out at sea, or .7 miles from the dock on a day sail.

[Valiente]

Originally Posted by btrayfors

6. The use of a single large battery bank for house plus a separate starting battery is the current preferred method, for several very good reasons.

7. You don't need to have them on a 1-Both-2-Off switch. A better arrangement for many installations is a simple ON-OFF for each bank (i.e., for the house bank and the starter battery).

8. Charging sources on a moderate or large-sized cruising vessel should all be wired directly to the house bank (not the starting battery). Use a battery combiner or, better, an EchoCharge device for keeping the starting battery topped off.

I singled these out as worthy of further comment. I am separating my current house bank (two 6v flooded SeaVolts) and my starter (a 12 V 1100 CCA on a Xantrex echocharger) into four 12 V 8Ds (probably AGMs) and the current 12 V starter. The reason is because I want the house batteries as close to the charger as possible (under the saloon stairs and out of the engine bay) in order to make both the battery cabling and the charge cables as short as possible. I plan on having the alternator output switchable to either the house bank-echo charger-start battery, or directly to the start battery. I anticipate that the alternator will feed the start battery primarily, as I plan to keep the house bank charged off shore power, and while cruising, via wind power, several 130 W solar panels and if necessary, a small genset.

When underway, I can opt to shunt alternator output to the house bank. The ideal is to avoid otherwise unnecessary engine hours simply for charging purposes. I would rather purchase (and have the space to stow in a low, cool, easily accessed spot) what some might consider excess house battery capacity in order to have a "cushion" for cloudy, hot, windless days at anchor when the fridge is eating amps, but also to "store" amps on the sunny, windy days in transit.

It sounds complex, but really I am saving in copper wire and terminals (except for the alternator to house bank wires, which will be about four feet) and simply adding a few selector switches, which will also aid in battery monitoring for state of charge, amp usage, temperature, etc.

My trim will improve by having weight slightly forward (nearly under the mast) and my battery health will be better served by keeping the batteries cooler...I will literally be able to open a step like a lid to blow a fan on them (or just let ambient air at them) while bulk charging, and access is ideal.

My experience with "best case battery system design" has been one of simple (on my old boat with just two car batteries that did both house/start functions) to complicated (charger/inverters, MPPTs, multiple charge sources, etc.) to simple again...as I grasp the implications and benefits of what I've learned, I am understanding how it is easy to make overly complicated decisions that only keep copper smelters happy!

[christyleigh]

Originally Posted by camaraderie

The MAJOR differences are that 6V T105 type is more easily moved as it is essentially 1/2 the size and weight of an 8D of similar 12volt amp hour capacity.

Cam - Ya.. as I just edited into my post after a head clearing walk, I was 'tunnel visioning' into 4D's as the 8D's are so damn heavy - especially when replacing them by yourself as I did the last 2 pairs

[camaraderie]

Stan...I did the four on mine and had to carry out the old ones too. I was not the same for a week! If you can imagine installing under a queen berth...with my head propping up the mattress and trying to lift and wrestle the 160lb. beastie into the battery box !! OOOOF!!

[poopdeckpappy]

As always, very good stuff posted here, someone mentioned a book a few posts back and I must concur.

As Cam said, 12 or 6 doesn't really matter as long as you do it right and keep it in good shape.

Also I think it's Lifeline that just came out with a 6v 300ah batt

[btrayfors]

Valiente,

I think I understand most of what you said, and it sounds pretty good in general.

However, I do not understand your reasoning, "When underway, I can opt to shunt alternator output to the house bank. The ideal is to avoid otherwise unnecessary engine hours simply for charging purposes." ?????

First, I don't see any reason to have a selector switch to shunt the alternator to either the starting battery OR the house bank, especially when you already have an EchoCharge device on the house bank which will put up to 15A charge into the start battery whenever it senses a charge voltage on the house bank (from alternator, solar panels, generator, etc.).

Remember that a start battery uses VERY VERY LITTLE total energy. Typically, they will use 150A to 250A for a few seconds to start the engine. Even a 250A draw for a slow-starting diesel, say 15 seconds, amounts to 1.04 amp hours....that's right, one amp hour. It won't take a 100A alternator very long to replace that one amp hour after starting the engine :-)

Say, a minute or two at worst. Now, what's that hefty 100A alternator gonna do now? Twiddle its rotor, I guess, wishing it could find something in need of a good charge like, maybe, the house battery bank :-)

Nah, just connect the alternator output to the house bank, connect your EchoCharge, and forget it. The starting battery will be kept fully charged and your alternator and house bank batteries will be happy!

Bill

PS...and don't throw any battery switches off while the engine is running!

B.

[christyleigh]

Originally Posted by btrayfors

Nah, just connect the alternator output to the house bank, connect your EchoCharge, and forget it. The starting battery will be kept fully charged and your alternator and house bank batteries will be happy!

The only other thing besides the above I've done to my last 2 boats is wire in a permanent positive 'jumper' cable with an on/off (I call it my Fail-Over) switch to connect the 2 separate banks if needed - hopefully never - for whatever.

[thekeip]

I've pretty much concluded that good system design comes in many flavors and one who is well read on the subject can't really go wrong. Most battery systems are fundamentally identical.
One thought that prevails though, is the notion that 6V golf cart batteries are somehow inferior to straight vanilla 12V units...they aren't....just the opposite, in my opinion.
Further, the fairly monsterous 8D's are, by design, diesel starting batteries...not deep cycle.
When these two notions are included in the equation the result may very well be the same but with many more interesting possibilities

Howard Keiper

[Maine Sail]

Just for grins I wanted to post this comparison.

One flooded 8D battery weighs about 135-145lbs., depending on the manufacturer, and produces between 210 & 225 amp hours using the industry standard 20 hour rating.

Two 6V T105 style or even Sam's Club 6V batteries weigh about 62 lbs each or 124 lbs for two and will deliver between 210 & 225 amp hours using the industry standard 20 hour rating. They will also have thicker plates than a standard 8D deep cycle and should theoretically last substantially longer.

So for the same amount of amp hours one 8D weighs on average slightly MORE than two 6V batteries yet it will break your back getting it on and off the boat!

The clincher is this though one 8D deep cycle battery is on average 21" Long by 11" wide by 10" inches tall for the for it's 225 amp hours of capacity.

So in a foot print of roughly 21 inches long (same length as ONE 8D) by 14 inches wide (only three inches wider than ONE 8D) and 10/3/8 high (only 3/8 of an inch taller than ONE 8D) you can fit FOUR Trojan T105's giving you DOUBLE the capacity at 450 amp hours in a a foot print only 3" X 21" bigger.

One 8D Deep Cycle = 225 AH at 21"L X 11"W X 10"T & weighs 135lbs.

Two 8D Deep Cycle = 450 AH at 21"L X 22"W X 10"T & weighs 270lbs.

Two T105 6V = 225 AH at 21"L X 7"W X 10 3/8"T & weighs 124lbs.

Four T105 6V = 450 AH at 21"L X 14"W X 10 3/8"T & weighs 248lbs.

To achieve an ah rating similar to the 6V's 450ah rating in smaller individual 12v deep cycle flooded batteries you could use four group 31 Trojan's (model SCS225) @ 225 amp hours each. Both the foot print and weight are slightly larger though.

Four Trojan Group 31 12V = 450 AH at 28"L X 13.5"W X 10"T & weigh 264lbs.

They do have thinner plates though and theoretically won't las as long as a comparable 6V.

That being said the Trojan SCS225 is an anomaly in group 31 12v batteries. Most group 31 12v batteries produce about 110 amp hours at the 20 hour rating not 225..




P.S. All measurements were rounded to the nearest..

[artbyjody]

A good FAQ site on batteries in general:

http://www.windsun.com/Batteries/Battery_FAQ.htm

and this:

http://marine-electronics.net/techar..._faq/b_faq.htm