# Lead Acid Battery - Battery Capacity Sensor for Microcontroller Input

Discussion in 'General Electronics Chat' started by Euclidjay, Dec 24, 2014.

1. ### Euclidjay Thread Starter New Member

Oct 11, 2013
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Good Day. I'm a graduating student and need a help regarding with my thesis, my final project, in college. Here's one of my problem in my project.

My project is using a Lead Acid Battery and Microcontroller (Arduino) what I want to do is when the Lead Acid Battery is going to be empty or about 10% of its battery capacity I need that to be an input in my Arduino. I've research sensors or circuits that can be input battery capacity in my arduino but can't find anything. Anyone there can help me? Please reply.

2. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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There is no single sensor that will provide this information. The true remaining battery capacity depends on many variables such as; initial charge, voltage, number of previous charge/ discharge cycles, age of the battery, temperature, rate of self-discharge, load etc. The best you can do is devise an algorithm which takes all these into account and estimates the remaining capacity. The manufacturer should be able to provide discharge curves which may be useful but these will be for a new fully-charged battery at a particular temperature and at a constant current.

3. ### Euclidjay Thread Starter New Member

Oct 11, 2013
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Thanks for your reply. Your reply make me sad because upon reading it, it just show how difficult to solve my problem but before I just want to share an idea. A while ago I've seen a 12V Lead Acid Battery Low Voltage Indicator

the concept of the indicator is

The BC557 PNP transistor controls the lighting of the LED. The BC557 transistors’ base is biased by the 10V zener diode. As long as the battery voltage stays above 11.6V, the zener keeps the base of the BC557 transistor high. When the battery becomes discharged, the zener stops conducting and the base bias goes low, and BC557 begins conducting, and the LED alerts you to the low battery voltage. You can use a variable resistor to fine tune the low voltage indication, and/or use a set resistor when you have a good value figured out.

based from what I know Lightning of the LED light can be an input to my Microcontroller (arduino). What do you think?

Oct 23, 2010
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5. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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You don't need any extra active circuitry if the micro-controller has an analogue input. Use a resistive voltage divider to scale the battery voltage to within the range of the A-D converter and measure it directly.

6. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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There is a *huge* difference between detecting a low battery condition and estimating remaining capacity or remaining discharge time.

#12 likes this.
7. ### #12 Expert

Nov 30, 2010
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Just last week, I met a car battery that was discharged. Its behavior about accepting charge from my battery charger convinced me that the battery is down to about 20% of its original capacity. This illustrates the idea that a, "remaining capacity" measurement is not obvious. You have to monitor the behavior of the battery during charge and discharge cycles to determine a guess about its capacity today.

8. ### MikeML AAC Fanatic!

Oct 2, 2009
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The concept of this circuit is no more than can be done any time with a Digital Multimeter. It is nothing but a voltmeter.
If you read the BatteryUniversity links, you will find that there is only a weak correlation between battery voltage and battery capacity.

9. ### ian field Distinguished Member

Oct 27, 2012
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You can get better resolution from the ADC by using a zener diode to drop a proportion of the voltage.

10. ### Euclidjay Thread Starter New Member

Oct 11, 2013
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Hello Guys thanks for your replies

Lead Acid Battery Capacity is solve. Since I only need to show what is the remaining capacity of my Lead acid Battery. I will just buy a 12v Lead Acid Capacity Tester from ebay.

The help I need now, is a connection to my lead acid battery and microcontroller. like the voltage reading to be ang input signal to my microcontroller. Anyone can help me?

11. ### bug13 Well-Known Member

Feb 13, 2012
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I don't think the eBay item can do what you want.

To get a simple voltage reading, you will need a voltage divider. (2 resistors in series)

12. ### Euclidjay Thread Starter New Member

Oct 11, 2013
24
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Hi Bug in my project lead acid battery capacity is different from voltage reading.
I think you are mistaken my explanation

Lead Acid Battery Capacity reading can be read thru that item which will be an output for my device

and What I need now is reading of voltage reading to be an inpout to my microcontroller and I think voltage divider can be an input to my microcontroller

Thanks bug.

Anyone suggest any other options?

13. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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I thought this had been explained earlier (several times), there is no such thing as an add-on battery capacity meter. This ebay device is really just a voltmeter that will tell you very little about the condition or capacity of the battery.

How do you propose to connect this device to the battery and micro-controller? You're the engineering student, you selected it.

Last edited: Jan 2, 2015
14. ### #12 Expert

Nov 30, 2010
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If you think that eBay battery tester can read capacity, and provide an output for your device, what kind of output do you think it will have? Current per amp-hour of capacity? A voltage per amp-hour of capacity? Do you believe the eBay battery tester is calibrated to your ADC input? If it is not, how would you correct the output?
Hint: Exactly what bug said.

bug13 likes this.
15. ### MikeML AAC Fanatic!

Oct 2, 2009
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What about there is only a weak correlation between battery voltage and battery capacity did you not understand?

Aug 2, 2010
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Jun 18, 2008
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