While we are on the subject of 6 volt vs 12 volt batteries, I thought I would
offer the following bit of fluff.
I am going to start off by saying something now that will not only surprise
you, but will cause you to doubt my sanity - Every MG TA, TB, TC, TD, TF, A,
B, and C has, and came from the factory with, ONE, repeat, ONE, 12 Volt
battery. It is also possible that your MG came from the factory with two 6
volt batteries. Obviously, now, I am going to have to explain myself.
When you return from the store with two 6 volt batteries under your arm, and
install them in your car, the instant you make the last connection, you have,
BY DEFINITION, a single 12 volt battery. Your single 12 volt battery just
happens to be in two boxes instead of one. Further explaination is in order.
Take a close look at the outside of one of your batteries. You will note
slight vertical depressions, equally spaced, on the front and back of the
case. These depressions are from the divider walls inside the battery, which
divide it into three cells. Each of these three cell produce 2 volts. They
are interconnected internally to the battery in series to produce 6 or 12
volts. On older batteries, the connectors were visible on the outside of the
case, but they are hard to spot on newer ones. By DEFINITION, a battery is
one or more cells, wired in series, parallel, or a combition of both, to
produce either more voltage or current than a single cell is capable of. On
the shelf, each box is a 6 volt battery, consisting of three 2 volt cells in
series. When you connect them, they become one 12 volt battery, with six 2
volt cells in series, in two containers.
Now, let's do a thought experiment. Imagine placing the two 6 volt battery
boxes side by side so that they touch each other. Next, connect the adjacent
terminals of the two batteries together, negative to positive. Since these
batteries are touching, we don't need two end walls where they touch. Let's
remove one of them, and glue the two cases together. Now that the two cases
are glued solid to one another, we can put the jumper connection inside the
case, just like the others. Now, stand back and look at what you have. It
looks a lot like one 12 volt battery, doesn't it.
The whole point of this exercise is to show that there is no inherent
difference between using two 6 volt batteries vs one 12 volt. However, all
other things being equal, a larger battery will have more storage capacity
than a smaller one. If we replace our two 6 volts with one 12 volt of the
same size as one 6 volt, and the batteries are of identical design, we have
obviously reduced our capacity. Refering to the above experiment, the
physical size is now half that of before. (I don't think it is safe to say
we have reduced capacity by 1/2, though. There are other parameters at play
here).
The flaw in the logic above is this - things are seldom, if ever, equal! A
good design 12 volt battery will provide more cranking power than two poorly
designed 6 volt batteries, even if each 6 volt is the same size as the one 12
volt. And vice-versa. It is very easy to buy a 12 volt battery that will fit
in the space allowed and provide ample cranking capacity for the intended
purpose. The fact that two sixes might provide more is of no concern if you
don't need the extra capacity. There is a lot to be said for having only one
battery to care for.
Don't be taken in by the claim that two 200 amphour 6 volt batteries will
have a 400 amphour rating. As you can see from the above experiment, the same
200 amps flows through both boxes. Battery 1 will use up its 200 amphours at
exactly the same time as battery 2. Which is exactly the same time a single
12 volt, 200 amphour rated, battery would have used up its 200 amphours. When
you decide on batteries for your MG, go by the ratings for a single battery,
whether you are using one 12 volt, or two 6 volt batteries. For our MGs, it
is simply a matter of choice. There is no compelling reason for either
option.
Personally, I have a 12 volt battery in my '74, and I have a storage bin in
the other space. For me, the choice was one of convenience.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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