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Bob UK
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Posted From: 94.197.122.73
Posted on Sunday, 14 December, 2014 - 07:22 am:   Edit PostDelete PostView Post/Check IP

The voltages below are for any flooded wet cell lead acid battery. Both deep cycle and starter batteries.

100% charge 1.265sg and 12.70v

75% 1.225sg and 12.40v

50% 1.190sg and 12.20v

25% 1.155sg. and 12.00v

0% 1.120sg. and 11.90v

Tolerance is +|- O.05v
temp 20c.
the above voltages are open circuit after equalization charge/discharge.

Float voltage is the amount needed at the battery terminals applied by a charger to offset self discharge.( often mistakenly called trickle) . 2.32v per cell plus or minus 0.05v.


Gas off voltage is 2.40v plus or minus 0.05v.

Notice that these figures are precise and apply to a motorbike battery and a submarine battery. They are like a constant.

My jeep has a volt meter which goes from 9 to 19v. Half way is 14 my needle stays just over 14v, 14.3 at a guess. This is just under gas off.
Anymore and the battery will gas. To maintain the battery at float charge the volts need to be 13.92v. There's barely 1/2 a volt in it.

To measure battery accurately a analogue voltmeter is no good.

I have made no mention of amps because amps are effected by the size of the battery and ate not constants. A float charge on a bike battery is probably 2amps but a submarine will be 100s.

Battery charging is a 3 step process.
1 bulk charge to 70% at 15% of amp hour rating. Here I take a bit of a liberty and go 30% for the first hour to burst any sulphate scabs on the plates.

2 once the open voltage is at 12.40v bring terminal voltage with charger connected to 14.20 volts.

3. 12.5v open circuit at the battery. Charge at 14v.

Note every time the battery voltage is checked the battery must be disconnected and a load applied for 15 secs, then open circuit check voltage. Car batteries, use headlamps. If the battery is not lloaded then the surface charge will make the volts higher and give misleading figures. Note how tight these figures are.

Unfortunately most battery chargers don't do the above unless they are monitored.

When bulk charging do not allow the terminal voltage to exceed 14.4v.

(Message approved by david_gore)

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