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battery specific-gravity = AmpHour capacity?
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? |
wrote in message oups.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 |
On Tue, 11 Jan 2005 00:35:58 GMT, "NSM" wrote:
wrote in message roups.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. |
Check out "Energy Primer Solar, Water, Wind, and Biofuels" by Richard
Merrill and Thomas Gage- Dell Publishing--accompaning and discussion on page 125. Graph shows both charge and discharge cycles with respect to amp hours, volts per cell, specific gravity, and amp hours returned over time. It appears that the specific gravity during discharge is linear with respect to amp hours discharged, but not linear with reguard to volts per cell. During charging, specific gravity of the cells over the charge time is not linear in respect to amp hours returned or volts per cell. It's a mindfull---good luck! |
And you're talking about the specific gravity of just the liquid
electrolyte, of course, not the entire cell. |
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 groups.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. R.F. |
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. |
On 16 Jan 2005 02:08:07 -0600, R. F. Burns R.F. wrote:
Battery terminal voltage is also an indication of specific gravity and SOC. AFAIR - no. But internal resistance of battery - yes. Best, Borek |
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