Sponsored By:

Subject: Re: [M]: OT: 12vdc to 18vdc converter and other stuff
From: Bill Arnett
Reply To: mapug@shore.net
Date: Wed Nov 27 01:38:21 1996

At 8:18 PM -0800 11/26/96, William Sommerwerck wrote:
>Chris_Vedeler@egghead.com wrote:
>
>> Most deep cycle batteries are rated for amp/hours. I have one in my
>> truck that is 500 amp/hours (I believe).
>
>As a fussbudget EE/tech writer/pain in the neck, may I get very, VERY
>picky for a moment?

Quite justified in this case, IMHO. There is a lot of misunderstanding in
this area which should have been trivial.

>Batteries are rated in amp-hours, NOT amp/hours...
>The reason I get SO UPSET about such things, is that it indicates that
>people are not paying attention to detail, and are using terms or
>concepts that they don't fully understand.

Worse, much worse, is the fact that most car batteries are rated in
"cold-cranking amps", a term with little meaning except that the numbers
tend to be large and hence impressive to unsophisticated buyers.
"Cold-cranking amps" have nothing at all to do with amp-hours. If the
battery you're considering doesn't have an amp-hour rating you can get
close by just comparing its volume or mass to an ordinary car battery
(which runs about 50 amp-hours). Or better yet, buy from a retailer honest
enough to use real units.

(I've always assumed that "cold-cranking amps" is that max current the
battery will deliver to a short-circuit for a few seconds at sub-zero
temperatures. Is that right? But being fortunate/clever enough to live
closer to the equator than the pole, I really don't care.)

---
Bill Arnett              billa@znet.com           http://www.seds.org/billa/

  "I know that I am mortal and the creature of a day; but when I search
   out the massed wheeling circles of the stars, my feet no longer touch
   the earth, but, side by side with Zeus himself, I take my fill of
   ambrosia, the food of the gods." -- Claudius Ptolemaeus (Ptolemy)