Rate Charge Lead Acid Battery 12V, 7.2Ah for charge 24/7

[DianWardiana]

Hi,

The battery datasheet is:
12 V, 7.2 Ah
Cycle use : 14.5V - 14.9V (25°C)
(Initial current : less than 2.88A)
Standby Use : 13.6V -13.8V

I'm planning to charge this battery for 24/7. So what the ideal current and voltage to charge this battery?

Regards,
Ian

 

[BradtheRad]

There should be a small trickle charge rate which feeds the battery sufficient Amperes to counteract its tendency to self-discharge. This charge rate might be a few uA to a few mA.
By experimenting over a period of days, you can find a charge rate which maintains the battery at a volt level between 12.6 and 12.8 V. The aim is to avoid causing electrolyte to evaporate.

Will you discharge the battery on a regular basis? Then consider increasing the charge rate, so that it gradually returns to spec standby voltage during the idle time.

 

[DianWardiana]

Hi,

Yes, i will discharge the battery on a regular basis.
If i charge the battery with 13.8V and 0.4 Amp is it safe?

Regards,
Ian

 

[KlausST]

Hi,

13.8V is a bit high for my taste. But it may work .... as long as the temperature is close to the specified 25°C.
Due to missing voltage cycling the lifetime of the battery may be reduced.
Also 0.4A constant current is far too high...see the recommendation for "uA or a few mA".

You may see a lot of "battery charging" threads here. And to all one can/should add the recommendation to read "battery charging" basics. A good source is: https://batteryuniversity.com
Go through the existing battery charging threads.

Klaus

 

[BradtheRad]

Yes, i will discharge the battery on a regular basis.
If i charge the battery with 13.8V and 0.4 Amp is it safe?

Here is a sample calculation. Each day suppose you draw 2.88A (your stated initial current) for 30 minutes. That makes 1.44 Amp-hours (equals 2.88 * 0.5).
Therefore you need to replace that amount every 24 hours. This means you can do this by feeding it 60 mA continually. (equals 1.44 / 24) That is a simple charging method.

 

[c_mitra]

Nominal battery voltage is 12V; for Pb acid cells, max voltage fully charged is 14.4V- you should never charge beyond this voltage (we use that as the cutoff value).

Fully down voltage is 10.8V; if discharged below this value, the battery will be damaged irreversibly. You should never allow the voltage to fall below 11.4V.

Under regular use, the battery should not be allowed to go beyond 12-13.2V (you should see this voltage with a meter during normal use.

All batteries has some leakage current- self-discharge- which is always talking place (including charging and discharging periods). The leakage depends on the total battery capacity and construction (and perhaps age).

For 7.2AH capacity, I would guess (hazard!) a leakage current of about 10-20mA. Some batteryman say that leakage is less under a nominal load (say 50mA for a battery of 7AH capacity). So your charging current should be more than 20mA (unless the voltage goes above 14V). Plus you add the loss during normal working (load discharge).

If you charge at constant voltage of 13.8V, the current will be around 100mA (will decrease slowly to 10-20mA over time) if the battery is partly discharged. You should limit current to 100mA (approx) and the voltage to 13.8V. Battery chemistry will take care of the rest. If it is a sealed maintenance free battery (most 7AH capacity batteries are gel type) you should not allow 400mA under normal charging.