Date: Mon, 19 Feb 2001 18:11:11 -0500
From: "Pres Waterman" <[EMAIL PROTECTED]>
Subject: Re: 50CT & 70CT batteries
If the load draws 1200mA you will get slightly
> >less than an hour off a 1200maH battery but maybe well over 2H from a
> >2400maH battery because the outflow is a lower proportion of its
capacity.
> >
> >This is borne out in practice with my wife's L50 and also my old L50J.
The
> >standard battery was under an hour. The extended battery with twice the
> >rated capacity was over 3 hours, so 2x battery gives 3.5x gain! Something
> >for nothing, almost.
>
> I get the jist of this... but I'm not clear on the details. Logically if
> the larger capacity battery is twice the maH rating, it should only last
> twice as long. But somehow because of the chemistry and electronics, the
> smaller battery ends up lasting less than its rtated capacity, and the
> larger one longer, huh?
For the same drain, yes, a larger capacity battery will be more betterer
because the load is a smaller percentage of the capacity.
Let's look at it this way...
Say a car took 1200 AMPS to start. Well, a 120 AH battery should crank it
for 1/10 of an hour, or 6 minutes. How many milliseconds would a 1.2 AH
battery crank it? 1/100 of an hour? Nope. Zero would be the answer. The load
is such a large fraction of the capacity it is overwhelmed.
How long would a 1200 AH battery ( they do exist, and they are big ) last on
a 1.2 A load? I dare say a long time. Because the drain is flea-size
compared to the ability.
Scaling it down a little bit, the smaller battery drains quicker on a more
closely matched load than the SAME load on a bigger capacity. The AMP-hour
rating neglects to specify the RATE at which it is drawn, and leaves the
user to assume it is linear. Not true. A 1.2AH cell may be rated at 1/10
output, or 120mA for 10H. But 2.4A drawn would be considerable less than
1/2Hour because the energy zooms out quicker and tires the poor little thing
down.
Note in all this we did not measure the Libretto's current drain, only
noting that it is the same on each battery. So that variable cancels out.
But I suspect it is about 1.5A or less. I think some have measured it
lately.
Thanks
Pres Waterman W2PW
c/o Patchogue Motors, Inc.
Long Island Ford and Kia dealer
GO BILLS!
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