On 16 Jan 2005 02:08:07 -0600, R. F. Burns R.F. wrote:
On Tue, 11 Jan 2005 10:22:51 +0800, budgie wrote:
On Tue, 11 Jan 2005 00:35:58 GMT, "NSM" wrote:
wrote in message
egroups.com...
| does specific-gravity of a conventional lead-acid cell, linearly
| measure its AmpHour capacity?
|
| If not, what exactly does it indicate with respect to the battery
| user's needs?
It's proportional to % of charge. I doubt it is linear. See
http://www.buchanan1.net/lead_acid.shtml
It is close enough to linear that some battery manufacturers provide
coefficients and/or graphs of SOC vs SG and temp.
It does of course require "calibration" to accomodate the actual acid/water
proportions at fill and any loss/replacement.
Battery terminal voltage is also an indication of specific gravity and
SOC.
Apart from being temperature-dependent, terminal voltage is very dependent on
recent charge/discharge history. Unless a known regime is implemented before
measurement, OCV can be very misleading as a SOC indicator.