The post describes simple battery charge monitor circuits or battery status circuits. The first design is a 4 LED voltage monitor circuit using the versatile IC LM324. The idea was requested by Ms. Piyali.
I've a project, if you could help me out:
1. basically its a battery voltage detector cum indicator circuit.
2. the output from a transformer is 6V, 12V, 24V resp., depending on the supplied input. O/p is A.C.
3. by converting it into D.C. I've to design a circuit which will detect and indicate the voltage o/p by colored LED lamps. Such as,
Blue LED - 6V
Green LED - 12V
Red LED - 24V
4. Circuit should be compact in nature as much as possible.
1. should we be using comparator circuit ?
2. how to detect the diff. voltage levels ?
3. Is relay required ?
Please consider at earliest.
1) The Design
The proposed battery voltage status monitor circuit using 4 LEDs makes use of comparators in the form of opamps from the IC LM324.
This IC is much versatile than the other opamp counterparts due to its higher voltage tolerance level and due to the quad opamps in one package.
In the proposed LED battery voltage monitor/indicator circuit all the four opamps have been used, although a few of them may be eliminated in case they are not required or depending on the specs of the individual users.
As can be seen the circuit diagram, the configuration is simple yet the outcome too effective.
Here the inverting pins of all the four opamps are clamped to a fixed reference level determined by the value of the zener diode which is not critical and can be any value close to the suggested one in the parts list.
The non-inverting pins of the oipamps are configured as the sensing inputs and are terminated with variable resistors or the presets.
How to Adjust the Thresholds
The preset should be adjusted in the following manner:
Initially keep all the presets slider arm shifted toward the ground end so that the potential at the non inverting pins become zero.
Using a regulated variable power supply apply the first voltage to be monitored starting from the lowest value to the circuit.
Adjust P1 such that at the above level the white LED just lights up. Fix P1 with some glue.
Next apply the second higher voltage or increase the voltage to the next level which is to be monitored and adjust P2 such that the yellow LEDs just switches ON. This should instantly shut OFF the white LED.
Similarly proceed with P3 and P4. Seal of all the presets after they are set.
The shown battery indicator circuit is configured in the "dot" mode meaning only one LED glows at any instant indicating the relevant voltage level.
If you want to make it respond in a "bar graph" mode, simply disconnect the cathodes of all the LEDs from the existing points and connected them all with the ground or the negative line.
Parts List for the battery status monitor circuit
- R1---R4 = 6K8
- R5 = 10K
- P1---P4 = 10k presets
- A1----A4 = LM 324
- z1 = 3.3V zener diode
- LEDs = 5mm, color as per individual preference.
The above circuit can be also configured in the following manner:
How it Works
The LED voltmeter discussed is generally used to track the charging and discharging of a vehicle battery. Because of its tiny size, it may be placed almost anywhere on the dashboard. The device is based on a low-cost quad opamp Type LM324, which may be powered directly from the automobile battery.
A comparison of the battery voltage and a reference voltage from each of the four opamp inputs generates the voltage readout. The reference voltage is generated using a zener diode connected to a bias resistor R1 and allowing a current of roughly 6 mA. 5V6 was chosen as the zener voltage because zener diodes running between 5 and 6 V have the highest thermal stability.
ALL THE LED CATHODES ARE SUPPOSED TO BE CONNECTED TO THE GROUND LINE.
2) Modifying the above 4 status Battery Indicator with Flashing LEDs
The above explained 4 LED battery status indicator can be modified appropriately for enabling it with flashing LED indicators, as shown in the following diagram:
- R1 = 2k2
- R2 = 100 ohms
- LED = 20mA 5mm type
- C1 = 100uF to 470uF depending on flashing rate preference
The article shows a simple method of using the IC LM3915 for monitoring battery voltages right from 1.5V to 24V in 10 discrete steps using 10 LED indicators.
3) Using a LM3915 IC for the 10 Step Function
The third circuit explained below allows you to visualize precisely what voltage your battery has at any particular instance while it's being charged.
The LM3915 is basically a 10 stage dot/bar mode LED driver circuit which provides a sequential 10 step LED display corresponding to the varying voltage levels set at its signal input pinout#5.
This input can be set with any voltage level right from 1 to 35V for acquiring a correspondingly sequencing readout of the voltages fed on that pin.
In the proposed 10 step battery charging indicator and monitor circuit we assume the battery to be a 12V which is to be monitored, the circuit functioning may be understood as follows for the aforesaid condition:
The transistor at the right end is configured as an emitter follower replicating a high current, constant voltage zener diode, fixed at 3V.
This is required so that the LEDs are restricted from drawing excessive current, unnecessarily making the IC warm.
The battery voltage is also fed to pin#5 via a voltage divider network made from a 10K resistor and a 10K preset.
The outputs of the IC are all connected with 10 individual LEds for producing the required 10 step indications. The color of the LEDs can be as per your preference.
How to Set up the above explained battery status indicator Circuit.
- It's pretty simple.
- Apply the full-charge voltage level across the point indicated "to battery positive" and ground.
- Now adjust the preset such that the last LED just illuminates at that voltage level.
- Done! Your circuit is all set now.
- For calibrating, simply divide the above mentioned full charge level with 10.
- For the present case, let's assume the full charge level to be 15V, then 15/10 = 1.5V, meaning each LED would stand for an increment of 1.5V. For example with the 8th LED just ON would indicate 1.5 x 7 = 10.5V, 8th LED = 12V, 9th LED = 13.5V and so on.
- Similarly, the circuit can be used with any battery and just needs to be set as per the above guidelines for achieving the proposed 10 step battery level monitoring.
Car Battery Voltage Monitor Circuit
The first concept above can be also modified as a 4 LED car voltmeter which will allow us to monitor the voltage level of the battery of our car at any instant, continuously.
To achieve the above feature it must be placed somewhere in the dash of the car so that the group of 4 LEDs remain protruded, each with a label indicating the battery voltage having at that instant.The circuit is designed for executing the following:
- 1st LED lights with 11V battery
- 1st and 2nd LEDs light with battery 12V
- 1st, 2nd and 3rd LEDs light with battery 13V
- 1st, 2nd, 3rd and 4th (all) LEDs light with battery 14V
When the battery voltage drops to 11 or 12 volts, it may need charging. If its around 13 volts it is in acceptable condition. At 14 volts it is fully charged. The colors of the LEDs indicate these status.
The main components of the circuit are just a few operational amplifiers used as comparators.
The inverting inputs of these operational are set at fixed reference voltages using resistor R1, and a zener diode D1 that may be rated at 3.3V or more, but below 6V.
The non-inverting inputs of the op amps are adjusted using the resistors R2, R3, R4, R5, R6. These may be calculated fixed resistors, or these may be replaced with 1 K presets so that the desired adjustment can be implemented for turning ON the LED at the respective battery voltages.
The battery voltage is delivered to non-inverting inputs of the opamps through the shown voltage divider networks formed by R4 and R6 terminals.
Depending on the battery voltage, the voltage at the non-inverting terminal will vary and will put a high voltage level at the output of the comparator, activating the corresponding LED for the required indications.
Parts list for the circuit
- IC1: LM324 integrated (quad opamps in a single integrated) Circuit
- D1: 3.3V zener diode, 1/4 watt
- D2 = D3 = D4 = D5: Diodes LED (2 red, 1 yellow or amber, 1 green)
- R1 = 1K
- R2.....R6: all 1K preset
+12V: is the car battery whose voltage is to be sensed
Another simple 4 LED battery monitor circuit is shown in the following image, using the IC LM324: