Battery capacity indicator

[user119]

Hi all,

I am looking for a battery capacity indicator for my Li ion battery pack. There are many battery capacity indicators available but unfortunately they are too big for my project. What I am looking for is a small capacity indicator that just displays the capacity in percentage that are found on cordless hair trimmers. Please refer to the image below.

TIA.

 

[BradtheRad]

It sounds as though you want to know the state of charge in the battery, correct? An Ampere-Hour meter is the instrument for that.

It keeps track of current going to or from the battery pack. The parameters it measures are: 1) how many Amperes in which direction, and 2) for how much time.

You can try measuring battery voltage and that gives you a rough idea moment-to-moment. However it doesn't do the same job as an Amp-hour meter.
It's possible to construct your own Amp-hour meter although it takes work and know-how and the right components.

 

[c_mitra]

Hi all,

I am looking for a battery capacity indicator for my Li ion battery pack. There are many battery capacity indicators available but unfortunately they are too big for my project. What I am looking for is a small capacity indicator that just displays the capacity in percentage that are found on cordless hair trimmers.

Battery capacity depend on several factors; age is one important one.

The capacity also depends on the rate of charging and discharging. If you discharge a battery fast, you recover less charge because some energy is lost in the battery.

Batteries are also subject to self-discharge but that is usually small and often ignored.

If your load is constant, you use a total charge calculator to get the per cent battery capacity left. They may be at most 5% accurate (because of aging and self-discharge)

You need a microprocessor controlled charge and discharge unit to that you get meaningful numbers on the display.

Simple voltage level based four level indicator modules are available for various cells (including Li-ion). For a battery pack, it can be messy.

 

[mtwieg]

The short answer is there isn't a simple way to add such a function.

At minimum, you will need:
1. A fuel gauge/coulomb counter chip (which must interface to the battery charge circuit so that it is reset when a charge cycle is complete)
2. A microcontroller to read the fuel gauge
3. The display itself, which is controlled by the microcontroller.