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12-18-2010, 07:12 PM
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CC Member
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Join Date: Sep 2002
Cobra Make, Engine: SPF#0760
Posts: 3,409
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Not Ranked
at 80 Degrees F
A fully charged battery (100%) will show 12.68V
12.24V at 50% charge
12.06V at 25% charge
Adgust these V #s by 0.04V for every 10 degrees colder temp
At 30 degrees a fully charged battery should show 12.588V
14.6 or 14.7 is fine for the charging system...
Have the battery checked with a load tester...
Blas
__________________
Wiring Diagrams: SPF MKII, MKIII, GT40, CSX7000, CSX8000, Corvette Grand Sport, and Shelby Sebring, Bondurant & Cinema Tribute Cars.
Owner’s Manuals: SPF MKII, CSX7000, CSX8000, Sebring, Bondurant, Cinema Tribute Cars $ GT40’s..
Large, easy to read and trace schematics with part numbers, wire colors, wire gauge, fuses, and electrical upgrade information. Trouble-shooting and replacement part numbers for those roadside repair adventures.
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12-22-2010, 09:20 AM
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Join Date: Oct 2003
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Quote:
Originally Posted by Blas
at 80 Degrees F
A fully charged battery (100%) will show 12.68V
12.24V at 50% charge
12.06V at 25% charge
Adgust these V #s by 0.04V for every 10 degrees colder temp
At 30 degrees a fully charged battery should show 12.588V
14.6 or 14.7 is fine for the charging system...
Have the battery checked with a load tester...
Blas
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Blas,
I must be missing something:
Using the figures above and your formula, I get 12.48V at 30 deg F.
.04 x 5 (50 degrees colder than the 80 degree value)= .2V.
12.68V (the 80 degree full charge value) - .2V= 12.48V
How do you get 12.588V for the 30 degree value?
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Chas.
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12-22-2010, 03:54 PM
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CC Member
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Cobra Make, Engine: SPF#0760
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Opps...a typo
~0.01v per 10 degrees...approximately...
All numbers taken from a battery/charging service article…
__________________
Wiring Diagrams: SPF MKII, MKIII, GT40, CSX7000, CSX8000, Corvette Grand Sport, and Shelby Sebring, Bondurant & Cinema Tribute Cars.
Owner’s Manuals: SPF MKII, CSX7000, CSX8000, Sebring, Bondurant, Cinema Tribute Cars $ GT40’s..
Large, easy to read and trace schematics with part numbers, wire colors, wire gauge, fuses, and electrical upgrade information. Trouble-shooting and replacement part numbers for those roadside repair adventures.
SPFWiringDiagrams@Comcast.net
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12-22-2010, 05:22 PM
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Join Date: Oct 2003
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Quote:
Originally Posted by Blas
Opps...a typo
~0.01v per 10 degrees...approximately...
All numbers taken from a battery/charging service article…
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Blas, thanks for the correction-makes more sense now.
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Chas.
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12-22-2010, 03:55 PM
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Half-Ass Member
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Join Date: Jun 2005
Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
Posts: 22,025
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Quote:
Originally Posted by ERA Chas
How do you get 12.588V for the 30 degree value?
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Chas & Blas, I don't think that's right. A lower temperature will increase battery voltage. Full-charge voltage on a 12-volt battery is 0.9 volts higher at 32°F than at 70°F.
Source: https://azsolarutility.com/Battery_Information.html |
12-22-2010, 04:08 PM
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"...A lower temperature will increase battery voltage..."
Not on the planet I live on... 
__________________
Wiring Diagrams: SPF MKII, MKIII, GT40, CSX7000, CSX8000, Corvette Grand Sport, and Shelby Sebring, Bondurant & Cinema Tribute Cars.
Owner’s Manuals: SPF MKII, CSX7000, CSX8000, Sebring, Bondurant, Cinema Tribute Cars $ GT40’s..
Large, easy to read and trace schematics with part numbers, wire colors, wire gauge, fuses, and electrical upgrade information. Trouble-shooting and replacement part numbers for those roadside repair adventures.
SPFWiringDiagrams@Comcast.net
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12-22-2010, 04:12 PM
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Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
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Quote:
Originally Posted by Blas
"...A lower temperature will increase battery voltage..."
Not on the planet I live on...
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The voltage increases as the temp goes down, but the capacity decreases. Here's another chart that shows the fully charged voltage ratings for 12v batteries at various temperatures. It increases as the temperature declines. http://www.powerstream.com/SLA.htm |
12-22-2010, 04:56 PM
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Location: Jacksonville,
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Cobra Make, Engine: Kirkham #570 w Shelby FE
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Unless your running EFI or have a stereo you should have only a couple circuits not cut off by the ignition. The "keep alive" memory for a computer (EFI) or the stereo will typically be less than 1ma (1/1000A). (leaking ign. switch is possible)
As stated, a leak at the alternator or regulator, starter solenoid, lights. While monitoring the battery voltage, pull fuses and disconnect the alt big lead. You should notice a couple tenths of a volt jump when you interrupt the leaking circuit.
Most DMM's have a 200ma current scale and usually a 10A scale, start with the 10A and work your way down. (placed in series with battery cable)
The big thing about batteries is the Amp/hours rating (not the CCA rating which is marketing BS for the most part). Typical car battery is in the 85 ~ 100 A/hr range: (1 amp for 100 hrs, 10A for 10 hrs, 100A for 1 hr.... You get the idea).
You'll probably find a leak of .5~2A from what your describing.
Worst thing they ever did was move from ampmeters to voltmeters on cars. (but hey, 12ft of 10ga copper wire is darn near $5!!) 
Last edited by Ronbo; 12-22-2010 at 05:03 PM..
Reason: afterthought
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12-22-2010, 05:18 PM
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Quote:
Originally Posted by patrickt
The voltage increases as the temp goes down, but the capacity decreases. Here's another chart that shows the fully charged voltage ratings for 12v batteries at various temperatures. It increases as the temperature declines. http://www.powerstream.com/SLA.htm |
Patrick those are charging voltages, not battery idle voltages (which will drop with temp.).
Both voltage and current will drop with temp (capacity in A/hrs). Or power if you will (IxE=P) If E (voltage) went up this would negate the decrease in current (I).
I'm sure we're all aware what effect that first freezing night has on that 5yr old battery we were going to change out. |
12-22-2010, 05:23 PM
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Quote:
Originally Posted by Ronbo
Patrick those are charging voltages, not battery idle voltages (which will drop with temp.).
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That would seem to make sense, and ol' Blas is usally right, but this quote: "Full-charge voltage on a 12-volt battery is 0.9 volts higher at 32°F than at 70°F" seems to be prevalent on several battery related sites. Is it completely wrong, or is there some subtle point we're missing? BTW, I pulled it originally from here: https://azsolarutility.com/Battery_Information.html |
12-22-2010, 05:26 PM
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Quote:
Originally Posted by patrickt
The voltage increases as the temp goes down, but the capacity decreases. Here's another chart that shows the fully charged voltage ratings for 12v batteries at various temperatures. It increases as the temperature declines. http://www.powerstream.com/SLA.htm |
Copied from your link:
While charging, a lower temperature will increase battery voltage. Full-charge voltage on a 12-volt battery is 0.9 volts higher at 32°F than at 70°F. While discharging, a higher temperature will increase battery voltage.
Emphasis is mine. As Ronbo says also, those are while charging and discharging.
But thanks to all for clarifying.
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Chas.
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