12 Volt Battery Monitor Circuit with LM3914
12 Volt Battery Monitor Circuit With LM3914
Accurately monitor battery voltage with LM3914 LED bar graph driver
storage | electric circuit | educationIn our article
Make a Simple Battery Status Monitor we showed how a few components could be put together to make a very basic
battery voltage monitor to give a visual indication of the charge state of a
12V lead acid battery.
Here we will show you how to make a more advanced
battery monitor using 10 LEDs (or an LED bargraph display) and the
LM3914 dot/bar display driver (pictured above) to show the battery voltage very accurately.
12V Battery Monitor Circuit
Above is shown the schematic for our
12 Volt battery monitor. The values of the resistors are R1 = 56K, R2 = 120K + 47K, R3 = 3K9 to give us an
11.89V to 12.65V voltage range - i.e. the first red LED (D1) will light up at a voltage of 11.89V which is a virtually empty 12V lead acid battery, and the last green LED (D10) will light up at a voltage of 12.65V corresponding to a full 12V lead acid battery. The other LEDs will turn on one by one as the measured voltage increases through the range.
To calibrate the monitor, connect it to 12.65V and adjust the 10K potentiometer (VR1) until the last green LED turns on. With the resistor values used, you will just need to check that the first red LED turns off as it should at 11.89V.
The
LM3914 has two modes - DOT and BAR. With DOT mode (as used in our example above) only one LED is on at a time. With BAR mode - achieved by connecting pin 9 to the incoming positive voltage - all LEDs up to the measured voltage are on at the same time like a bar graph.
In DOT mode the circuit shown above would draw under 10mA. In BAR mode the current consumption would be increased by an amount depending on the number of LEDs turned on.
To change the
brightness of the LEDs, R3 can be changed. Increasing the value reduces the brightness (and also reduces current consumption), decreasing the value increases the brightness (and also increases the current consumption). Replacing R3 with a
variable resistor in series with a 1K resistor enables the brightness of the LEDs to be easily changed for example for indoor or outdoor use.
Instead of using 10 individual LEDs, an alternative is to use an
LED bargraph display such as that shown above. It is basically 10 LEDs packaged nice and small and tidy. These are available in a range of different colours and sizes here:
LED Bargraph Display.
Changing the Battery Monitor Voltage Range
Changing the
voltage range for use with different types of battery or any other reason is very easy. The upper limit is set with the 10K pot as during calibration - just connect the desired upper limit voltage (above which the last green LED will turn on) to the monitor and adjust the 10K pot until the last green LED just turns on.
Adjusting the lower limit is a bit trickier. Replace the R2 resistor(s) with a
200K potentiometer (as shown above), connect the desired lower limit voltage to the monitor and adjust the 200K potentiometer until the first red LED just turns on. You can leave this 200K pot in place, but for reliability it is better to measure the resistance across the two potentiometer terminals connected in place of R2 and then replace the potentiometer with fixed resistors totalling the measured value.
The above steps are made very much easier if you have access to a
variable voltage power supply.
More Information
Click here to buy an
LM3914 LED Display Driver, and here for the
LM3914 Datasheet for more technical information.
Article Last Modified: 13:09, 4th Aug 2012Comment on this Article
If you have any comments on this article, please email them to
neil@reuk.co.uk.
Recommended Related Articles
People who read this article also enjoyed the following articles:
LED Dimmer CircuitFind out how to put together a simple but efficient PWM dimmer circuit for LEDs
Article Last Modified: 09:42, 16th Mar 2011lighting | electronics | electric circuitDynamo Hubs For Wind TurbinesDynamo Hubs and bottle dynamos for use in small DIY wind turbine generators
Article Last Modified: 12:18, 11th Apr 2009wind | electronics240V LED Bulbs and Dimmer SwitchesFind out more about 240V AC LED bulbs and dimmer switches
Article Last Modified: 16:12, 16th Jul 2007lightingMake a Simple Battery Status MonitorMonitor battery status with this easy electric circuit project - no skill required!
Article Last Modified: 12:33, 16th Mar 2007storage | electric circuitSolar Panel Mounting AngleFind out how to position a solar panel to maximise power output
Article Last Modified: 08:08, 12th Dec 2012solar | educationMake a Mini Wind Turbine Battery ChargerConvert a PC fan into a wind turbine battery charger
Article Last Modified: 20:19, 7th Aug 2012wind | electronics | educationFuel CellsIntroduction to Fuel Cell technology and its benefits and disadvantages
Article Last Modified: 20:52, 17th Dec 2012transport | electronicsSolar Water Heating Swimming PoolsBuild a solar powered water heating system for a swimming pool
Article Last Modified: 10:06, 8th Oct 2012solar | water | heatingTL431 Battery Voltage MonitorMonitor the voltage of a battery or battery bank using an TL431 (aka LM431) shunt regulator
Article Last Modified: 16:42, 11th Jun 2007storage | electric circuit | electronicsReverse Polarity ProtectionProtect your circuits from reverse polarity power connection
Article Last Modified: 15:32, 13th Aug 2012electronics | electric circuit | education
|
|
