Electronic – How to attain a topping charge for a lead-acid battery

batteriesbattery-charginglead-acidlithium ion

Charging a lead-acid battery involves three stages: CC, CV, and Float. I have a charge controller which charges my battery at CC to the float voltage. I would like to add a device that would charge it via CV to full charge. (See Lead Acid Battery Charger Design Factors for description of stages.)

For example, I could attach something that would charge it, keeping it at 14.6V until the current goes down to .1A, and turn off. When this device would turn off, the charge controller would kick in, and keep it at 13.7V Float stage.

However, I cannot find a device that would do that:

1) Charge controllers that have a "Absorbtion" 14.6V stage typically have it timed,
    say for 10 minutes, and then turn off regardless of the current.
2) Charge controllers that I can program to rise to 14.6V indefinitely, have no way
    to tell me when their current goes low enough (other than through an LCD display).
2a) I can attach a timer to turn off such a controller after giving it enough time to
    reach .1A current; however, since my system if powered by solar panels, it might
    not reach .1A within that time frame on a cloudy day.
3) I can use a CC / CV power module to output 14.6V; however, that will not measure
    the voltage of the battery, nor determine when the battery is fully charged.
4) I have bought several commercial chargers, such as ElProg Pulsar, capable of doing
    such a charging; however, all of them require at least pushing a START button to
    initiate the charge.

I have consulted with my dad, who's an electrician; however, all options have gave are either very power-consuming (e.g. involving PLC), or are not available at 12V.

I am open to buying a commercial product that would do this, if it is too complicated to make by myself. Please give some advice.

Best Answer

Generally speaking, the topping charge is done by keeping the battery voltage at the equalize voltage until the current drops to some fraction of the charge current.

I've built several simple lesd-acid chargers over the years but mine are two-state chargers - the charger drops out of equalization mode when the charger drops out of constant current mode.

It would be easy to add a circuit that keeps the charge voltage at the equalize voltage until the current drops to perhaps 10% of the constant current value. You do need that threshold to be higher than any current that your circuit consumes.

I'll have a look at my most recent charger version and see how easy it is to do

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