Battery Charge Remaining (Fuel Gauge) for Various Replaceable AAA

[mudandsnow]

Hello,

I am working on a product that runs off 1 AAA battery. There is no charger in it and the user will be replacing the battery anywhere between every use and every 10 uses.

My goal is to give an accurate indication of how much charge is remaining or at least steps of 25%. I worry that might not be feasible since users can insert any type of AAA at any charge level.

I've looked at various fuel gauge ICs but I'm not sure if they can handle a battery being inserted when half charged.

Am I asking for too much or does this sound possible?

Thanks.

 

[itsmoked]

Nope a 'fuel gauging' circuit can not work in this application. The normal solution is a direct battery voltage measurement. On a product like this you would measure the voltage under load and go to a pre-created, via experiment, look-up table to provide the 'remaining' indicator/display with the appropriate battery remaining value.

Alkali batteries have a dependable voltage drop with SOC. (State Of Charge)

You the designer have to understand what that means under your product's loading on the battery.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mudandsnow]

Thanks for the reply. I am measuring battery voltage under load (Vbat_loaded) of about 500mW. That works with barely acceptable accuracy for low SOC but with mid or high SOC there is too much difference between the different battery chemistries to determine SOC based on Vbat_loaded without knowing the battery chemistry.

Is there any way to determine battery chemistry through measurements?

 

[Comcokid]

You need a battery monitor IC.
Go to Digikey.com I suggest them because they have a good search engine and accurate data base.
Select: Product Index > Integrated Circuits (ICs) > PMIC - Battery Management
There are almost 4,000 parts in this category.
Check the 'In Stock' box. No use looking for devices that aren't popular.
Under 'Part Status' select 'Active'. No use looking for obsolete parts.
Under 'Battery Chemistry' select 'Multi-Chemistry' This will get you ICs that among other things at least support alkaline cells. Also, I didn't see a direct selection for 'Alkaline' or 'carbon zinc'.

Begin looking at data sheets. This will help you better understand what features are available, which vendors may be making devices more like what you need, and help you understand the features.

 

[mudandsnow]

Thanks Comcokid. Digikey is my preferred vendor also. 'Fuel gauge' means battery management IC that does SOC measurement.

Have you seen any ICs or methods to measure SOC for unknown AAA chemistry that can be inserted at any SOC?

 

[3DDave]

You can guess the chemistry from the open circuit voltage. What you can't guess is the Equivalent Series Resistance, which will depend on the construction of the cell. Without the base ESR you won't know how much voltage drop is from electrolyte exhaustion and how much from basic construction.

The problem with estimates of percent consumption is that it doesn't tell anything useful about how long a cell will last.