Battery charger

Pim Driessen · Oct 29, 2020

Dear Forum Members,
To supply my microphone amplifier with voltage I bought a battery of 12 volt 1.3 Ah, Nedis Lead Battery BALA1300 12 Volt.
Finding a charger for this is not that easy, because this battery must be charged with 300 mA.
Most battery chargers that can be found on the web start at 600 mA with charging, which does not seem good for the life of my battery.
Now I wondered if it is not possible to make a charger with an LM317 that has a charging current of 300 mA, but which also stops charging when the battery is full.
Does one of the Forum members have an idea to solve this problem?
Greeting,
Pim

crutschow · Oct 29, 2020

You can readily adjust the charge current of an LM317 to 300mA but, to determine when the battery is full, you need to monitor the current and shut off the charging when it drops to a low level.
That requires more complicated circuitry or a microprocessor to monitor the charge.

The best solution would likely be to purchase a smart charger with a 600mA limit which automatically drops to a trickle-charge when the battery is full, and add a series current limit circuit for 300mA to its output.

A simple two-transistor current-limit circuit is shown below.
It limits the battery current (green trace) to 300mA.
As the battery voltage rises (horizontal axis), the current drops and, at some low current, the smart battery charger should drop to a lower voltage trickle-charge.

Pim Driessen · Oct 30, 2020

Dear Crutschow,
Thanks for the advice, I'll be working on that.
Greeting,
Pim

gophert · Oct 30, 2020

A good 600mA charger will be fine with a lead acid battery (1.3Ah). As long as the charger has voltage control it will adjust as needed. Here is some advice from battery university...

**broken link removed**

Argument about Fast-charging
Manufacturers recommend a charge C-rate of 0.3C, but lead acid can be charged at a higher rate up to 80% state-of-charge (SoC) without creating oxygen and water depletion. Oxygen is only generated when the battery is overcharged. The 3-stage CCCV charger prevents this from happening by limiting the charge voltage to 2.40V/cell (14.40V with 6 cells) and then lowering to a float charge about 2.30V/cell (13.8V with 6 cells) at full-charge. These are voltages below the gassing stage.

Test show that a heathy lead acid battery can be charged at up to 1.5C as long as the current is moderated towards a full charge when the battery reaches about 2.3V/cell (14.0V with 6 cells). Charge acceptance is highest when SoC is low and diminishes as the battery fills. Battery state-of-health and temperature also play an important role when fast-charging. Make certain that the battery does not “boil” or heat up during charge. Put an eye on the battery when charging above the manufacturer’s recommended C-rate.

Pim Driessen · Oct 30, 2020

Dear Gophert,
Thanks for the information.
Greeting,
Pim

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