[C320-list] Are 6V Batteries Superior To 12V Batteries

[Jeffrey Hare]

Steve, 

I completely agree with you on your last point (only for those on extended
cruises in more primitive foreign waters):

  "you can mix and match your remaining batteries 
   to get adequate power if things are going south
   on you."

That's really the only meaingful advantage I see...

That said, I don't believe this statement is really true: 
 
  "If one cell shorts out in a pair of 6 volt
   batteries, only one of the two batteries 
   needs to be replaced for only [small]$."

...unless the shorted cell dies immediately after installation (in which
case, a quality battery should have a warrantee to cover that).  

If you lose a cell in a 6V battery mid-life, you still **must** replace both
6V batteries in the series pair.  You cannot mix a new 6V battery in series
with an older 6V battery with many cycles on it (if you expect either to
live very long).  A new and an older battery simply do not recharge in
compatible ways.

It would still provide 12V and work for a while, but since the name of the
game is Amp Hours & battery life, you've really lost big in those
departments.   Mixing new & old limits the capacity, prevents properly
charging the series pair, and radically shortens the life of both (meaning
buy replacements way sooner.)  

PLUS you must have the ability to separately charge and equalize each of the
6V batteries from time to time in order for them to live as long as a 12v
battery.  (MEANING access to a 6V battery charger with equalization
capability!)

The key premise for going with 6V batts was getting more Amp hours
per-dollar-spent over time, so if you don't get what you're paying for, are
you really saving money or do you just feel like your saving money?

You can get decent 4D batteries for $120 and up, and if you put them in
parallel, you'll have a simple reliable system with lots of power available.

===================================================================
Here is an excerpt from Ample Power's over 6V vs. 12v batts:
===================================================================
"... a (12V) 100 Ah battery can be placed in parallel with a 200 Ah unit to
obtain a total of 300 Ah. Charging proceeds as expected, with each battery
receiving its share of the charge current, and each reaching a full charge
at the same time. On discharge, each battery supplies current according to
its relative capacity, and both batteries maintain the same percent depth of
discharge.

Contrast this with two 6 Volt units. With series connected units, each
battery must be of equal *capacity*. [...] Despite close manufacturing
tolerances, each supposedly identical battery has different capacity. When
the specific gravity is different in each, capacity is further affected.
Deep discharges of series cells can cause the weaker cell to be reverse
charged. A weak cell in a series string can cause other cells to be
overcharged. [...]  For best results, 6 Volt batteries should be
periodically charged individually and should definitely be equalized
individually..."

In other words, if you want the promise of the rated amp hours, long life
and economy, it's a lot more work and attention to details most of us don't
want to deal with, all that for only few more Amp Hours at best.

Stick with 12V batts and go sailing.  :)

-Jeff

-----Original Message-----
From: Steve Magennis [mailto:magenns at yahoo.com] 
Sent: Monday, June 26, 2006 8:44 AM
To: C320-List
Subject: Re: [C320-list] Are 6V Batteries Superior To 12V Batteries

One additional item that most people are dancing around:

If one cell shorts out on a 12V battery, the battery is shot and needs
to be replaced for $$.  If one cell shorts out in a pair of 6 volt
batteries, only one of the two batteries needs to be replaced for only
$.  In addition, you can mix and match your remaining batteries to get
adequate power if things are going south on you.

Steve
Alchemist #909

--- Warren Updike <wupdike at hotmail.com> wrote:

> I can't disagree with much that's been said.  However, I've not see
> the arguement on price and capacity.  I don't know why it is but I
> understand golf cart batteries have about 200 AH capacity.  Also,
> golf cart batteries can be found at Sam's Club, BJ's, and I presume
> CostCo for quite a bit less than equivalent 12V 4D from the likes of
> BoatUS.  Price of about $60 seems to ring a bell.
> 
> A number of people have replaced two 4Ds with four golf cart
> batteries.  Total amp hour capacity goes from about 270 to 400+ AH 
> for less money.  Unless there is a kickker, that sounds like a good
> deal.  Compare the dimensions of the golf carts vs 4Ds.  I understand
> they are a bit taller, but otherwise fit in the same horizontal
> space.
> 
> I chartered a 52' Tarten in BVI and the captain said he has 12 6V
> golf cart batteries on board because they are much less expensive to
> buy, weigh less (easier to install/remove,) and have more reserve
> capacity than equivalent marine deep-cycle batteries.
> 
> Warren & Pattie Updike
> C320, #62, 1994, "Warr De Mar"
> Frog Mortar Creek, Middle River
> Chesapeake Bay
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com