Detecting non-rechargable battery health, in-line

[jayachar88]

I have a miniature datalogger running which is powered by either a small non-rechargable Lithium battery (CR2013) or a set of 3x 1.2V Alkaline AAA cells. A bi-color LED is made to blink green when it is in operation and healthy.

I just need that LED to glow red (& possibly a piezo buzzer start buzzing) when the CR2013 battery is nearing exhaustion and needs to be changed. Can someone help me figure out the circuit that can monitor the health of non-rechargable batteries -- note 2 different chemistries (but in 2 different type of circuits). This monitoring needs to happen in parallel, i.e. while the the battery is powering the data-logger circuit as well.

I am looking at all possible options, especially ones that are economical, i.e. these are not mission-critical dataloggers.

~Jay

 

[mister_rf]

Read here:
https://www.edaboard.com/threads/119926/
You may use some low voltage standard CMOS Voltage detector ICs, see some examples:
**broken link removed**
**broken link removed**
Power Management ICs - Supervisory IC product family, voltage detector, battery monitoring - austriamicrosystems

 

[luben111]

you should measure the voltage of the batteries through ADC every 10-30s. You can use oversampling to increase the ADC resolution from 10 bits to 12 or 14 bits. So if the voltage is under some threshold you change the LED color. Also you need some algorithms to detect which kind of battery you have so you change the thresholds according to the type of the battery

 

[jayachar88]

@luben11, thanks a lot. The MCU I am using currently for the datalogger (prototype) doesn't have ADC (for cost reasons). I could swap for a MCU w/ADC but that bumps us my cost by about $3-$4 (in small quantities)... something which hurts it's economic potential. However, I'll definitely give this some serious consideration.

As for detecting battery type, I am absolutely okay to throw in a dip-switch for that, as the battery types are 2 different products, but only from battery standpoint, rest all is same from electronics standpoint.

Not familiar with ADC oversampling, so will need to check that out. However, I am wondering if 10-bits would really be insufficient ? I'll probably have to think this thru a bit more, but I was thinking of something like:-

Standard Alkaline 3-cell battery --
Healthy: 4.5V
Needs-replacement: 3.6V or less
that's a significant 20% drop, and a 10-bit ADC should be able to help me determine this.

Another approach that might be possible, could be using the Comparator (the low end MCU has Comparator, no ADC). At least for Alkaline batteries, I guess the terminal voltage drop is a sufficient indicator, but is it so for Lithium batteries ? I see some really complex ways in which some Battery-Management SoC's do "Battery Guage" maintenence... although I guess much of it is for highend consumer-grade devices.