battery specific-gravity = AmpHour capacity?

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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?

 

[Sam Wormley]

does specific-gravity of a conventional lead-acid cell, linearly
measure its AmpHour capacity?

What happen is you double the battery's volume?

If not, what exactly does it indicate with respect to the battery
user's needs?

Try: http://www.universalsolutions.com/techdocs/RTCPAUFVP.pdf
http://www.faqs.org/docs/electric/DC/DC_11.html

 

[NSM]

| 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

 

[budgie]

| 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.

 

[electroninja]

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!

 

[Sbharris[atsign]ix.netcom.com]

And you're talking about the specific gravity of just the liquid
electrolyte, of course, not the entire cell.

 

[R. F. Burns]

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.

 

[budgie]

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.

 

[Borek]

Battery terminal voltage is also an indication of specific gravity and
SOC.

AFAIR - no. But internal resistance of battery - yes.

Best,
Borek