Lead acid car battery question ?

Im using a 12v lead acid car battery to power a 10 amp motor how low should i let the terminal voltage under this sized load go before disconnecting the load and recharging without the battery suffering permanent loss of performance ?

a car battery is generally classed as discharged below 12v, a deep cycle battery can take a bit more punishment

These are general voltage ranges for six-cell lead-acid batteries:

Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)

Open-circuit at full discharge: 11.8 V to 12.0 V

Loaded at full discharge: 10.5 V.

Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells

1.All voltages are at 20 °C (68 °F), and must be adjusted -0.022V/°C for temperature changes.

2.Float voltage recommendations vary, according to the manufacturer's recommendation.

3.Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)

Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)

Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.

Gassing threshold: 14.4 V
After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.

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The above information was taken from here.

It is important to note the first portion where they mention:

Open-circuit at full discharge: 11.8 V to 12.0 V

Loaded at full discharge: 10.5 V.

Full discharge under load is about 10.5 volts. Let the voltage drop below that and you destroy your battery. Open circuit will show about 11.8 to 12.0 volts when the battery needs recharged. A fully charged lead acid battery should read about 12.6 volts.


Ron

If i let the terminal voltage across the battery drop down say 10.8 (for safety) volts under load will that be good for a couple 100 cycles ?

At 11v under load what discharge depth is that for the battery ?

tron87 said:

If i let the terminal voltage across the battery drop down say 10.8 (for safety) volts under load will that be good for a couple 100 cycles ?

At 11v under load what discharge depth is that for the battery ?

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A standard automobile flooded lead-acid battery is NOT A STORAGE battery; it is a STARTING battery. Discharging a starting battery below 50% just once will greatly reduce its capacity. A Deep-Cycle Storage battery will take repeated charge-discharge cycles; an automotive starting battery will not!

The reason is the way the plates are constructed. They are sintered, which means the lead plates are porous (sometimes called spongy lead). If you repeatedly discharge below ~75% of its rated capacity (15aH out of an 80Ah battery), the lead that deposits back onto the plates is no longer spongy, meaning you have reduced the surface area of the plates, and this causes the capacity and the cranking Amps to be greatly reduced.

Think about this. You do the D.S. thing and leave your headlights on for 24 Hours. You come back and find the battery dead. You jump it or charge it, and drive the car for a few months, but then about the time the weather gets cold you're buying a new battery, even if the battery was relatively new. Just one deep-discharge is sufficient to alter the makeup of the battery such that its capacity is reduced by 70% or more.

Car batteries are simply not designed to be discharged; EVER!!! If you dont believe me, Google it.