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

[Jeffrey Hare]

Hi Warren,

   Putting a pair of 200Ah  6V batteries in series yields roughly 200Ah, not
400ah, since they don't add in this way.  They only add when placed in
parallel.  So regardless of whether you go with 4 golf cart batteries or 2
4Ds, you'll end up with roughly 380-400ah either way.

6V battery pairs in series have their ...

Advantages:
===========
1) Weight ~1/2 each

2) Price (maybe, see disadvantages)

Disadvantages:
==============
1) Both batteries **must** have the same number of cycles on them, be the
identical internal construction and mfgr to use in series.  AND YOU MUST
REPLACE THEM IN PAIRS or you're just tossing away money since the older
battery will fry itself.

2) The Amp Hours available in the weaker battery RULES since they're in
series.

3) Doubles the number of terminal connections. Most people rarely clean
these terminals and connectors.  If you're one of these people, 6V systems
won't be providing you extended usable AH you expect due to increased
resistance.  (and it is significant).


Now, for the AMP HOUR issue:

Remember that the usable Amp hours depends a lot on the condition of every
connection, and the rate of draw-down.  There's a lot of "smoke and mirrors"
in the Amp hour numbers, so don't be fooled there.  They can use thinner
plates and achieve better numbers at the expense of durability and cycles.


Here's a Quiz:  :)
===================

ASSUME: A 200 Amp Hour (4D 12v battery) or (pair of 6V golfs in series):

Question:  If you remove 100AH from the battery, how much do you have left?

Answer: DEPENDS ENTIRELY on how *fast* you removed that 100 Amp Hours!

If you put a 100A load on the battery, it could be completely spent in under
10 or minutes or so.  That's less than 60 amp-hours till dead battery.

Yet, if you draw the battery down with a 1 amp load, you could go way over
200 hours before it's drained, maybe even 300 hours.  That'd be 300 amp
hours.

This is why, if you want to get maximum usable amp hours out of your
batteries, PUT THEM IN PARALLEL.  It instantly cuts the draw from each
battery in half and will give you more usable amp hours out of the battery.
The ADDED BONUS here is that the slower you draw down your batteries, the
less they're damaged by discharging, so LONGER LIFE.


My recommendation is, and has been,  Put 4Ds in parallel, add the biggest
Automotive starting battery you like (900cca or better), go sailing and let
the next owner deal with changing the house batteries..  :)

-Jeff


-----Original Message-----
From: Warren Updike [mailto:wupdike at hotmail.com] 
Sent: Sunday, June 25, 2006 9:51 PM
To: Catalina 320 Mail List
Subject: Re: [C320-list] Are 6V Batteries Superior To 12V Batteries

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