12v battery monitor circuit help!!!!

[wireengineer]

Hi guys,

im trying to find a circuit that will monitor a 12v battery and if the voltage drops below 10v it gives a visual of sound output (LED or BUZZER).

Thanks in advance guys.

(i have found this circuit....Circuit - 9v Battery Voltage Monitor using a LTC1440 comparator - Circuits designed by David A. Johnson, P.E. but i am unsure how to alter it to meet my needs)

 

[canadaelk]

Varying the ratio of R1/R2 will change the voltage drip point. Increasing R1 will increase the voltage. E

 

[JimB]

In the circuit shown in the link, you can define a threshold voltage and R2 and use this form of the equation to calculate R1.

R1 = R2 x (V - 1)/1.18

If we set the threshold at 10 volts and the value of R2 to 620k ohm, R1 will be 4.7M ohm.

The actual threshold will of course depend on the actual values of R1 and R2, depending on the tolerance of the the resistors used.

JimB

 

[wireengineer]

JimB. So if i alter the resistors to the values you suggested the cut off point will be at 10v?

 

[JimB]

Yes.

But as I pointed out, the exact switching point will depend on the tolerance of the resistors.
But if that is a problem, there are several easy ways to overcome the problem.
1 selecting resistors
2 adjusting resistors by putting a second resistor in parallel
3 adding a variable resistor into the R1/R2 diveide chain.
4 etc etc

JimB

 

[wireengineer]

As long as it's around the 10v level that's fine but I may mount them in parallel to make sure. Also if I supply the circuit with 12v instead of 9v what else will I need to change?

 

[JimB]

The LRC1440 is only rated to 11 volts, so the supply voltage will have to be reduced.
I would do this with a simple zener diode voltage regulator, see the attachment.

It also occurs to me that the value of R3 is a bit on the low side for the average LED, I think it will be a bit dim. If you want your LED brighter, try reducing R3 to 1k.

JimB

 

[colin55]

Here are two simple circuits to monitor your battery:

**broken link removed**
A very simple battery monitor can be made with a dual-colour LED and a few surrounding components. The LED produces orange when the red and green LEDs are illuminated.
The following circuit turns on the red LED below 10.5v
The orange LED illuminates between 10.5v and 11.6v.
The green LED illuminates above 11.6v

**broken link removed**
This battery monitor circuit uses 3 separate LEDs.
The red LED turns on from 6v to below 11v.
It turns off above 11v and
The orange LED illuminates between 11v and 13v.
It turns off above 13v and
The green LED illuminates above 13v

 

[wireengineer]

JimB thanks for all your help! The circuit schematic looks perfect, do you think this configuration will work for me?

 

[JimB]

do you think this configuration will work for me?

If you want a voltage monitor which is powered from the supply which it is monitoring, then yes, it will work for you.
Why do you think it may not work?

JimB

 

[wireengineer]

Hi,

Just made a copy of the circuit using my software. Does it look ok to you JimB?

 

[JimB]

Not quite right, the 1.18 volt zener is internal to the LTC1440, it is only shown on the datasheet drawings to help understand the operation, delete it from your drawing.

Connect pins 4, 5 and 6 together, as they are now but without the diode.

Connect pin2 to the -ve supply line, the same as pin 1.

JimB

 

[wireengineer]

Ok, so i think iv fixed the issue??

 

[wireengineer]

In the schematic there is a 8.2v zener diode for the voltage regualtion to the LTC1440. Is this diode suitable...

NXP | Semiconductors | Discretes | Zener | Zener Diodes 1.3W |BZV85-C8V2

 

[gilmanli]

Made it as simple as possible ! 12v turn on the LED otherwise those LED turn off.I think one trasistor,a few resistors and one red LED can fulfil this function.

 

[JimB]

In a PM, wireengineer wrote:

***********************************************************
Hi JimB. Thanks for all the replies on the following link...

12v battery monitor circuit help!!!!

I was just wondering if you could help me' with one more thing. Could you please explain to me' the theory of operation behind the circuit?

Thankyou!
***********************************************************

I prefer to answer in the forum, then others can benefit from the information.

First, have a look at the datasheet:
https://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1002,C1463,P1172,D2764

Second, the LTC1440 works by comparing the voltage at pin3 with the voltage at pin4.
When the pin3 is a higher voltage than pin4, the putput at pin8 is high , when pin3 is at a lower voltage than pin4, the output at pin8 is low.
The voltage at pin4 is the reference voltage form the zener, the voltage at pin 3 is the supply voltage divided by the potentiometer R1/R2.

JimB

​

 

[wireengineer]

JimB, is there another alternative to the Zener diode voltage regulator as I cannot get the section to work. Also if not how long could the comparator work at 12v for?

 

[JimB]

JimB, is there another alternative to the Zener diode voltage regulator as I cannot get the section to work. Also if not how long could the comparator work at 12v for?

Also in a PM, wire engineer wrote:

I have a little question for you. What is the best way of reducing 12v to 11v? I have tried using an 8.2v Zener diode but i can't figure it out. Are there any other methods?

Looking back at the circuit as you have drawn it, the zener diode is connected the wrong way round, compare with my circuit earlier in the thread.

JimB

 

[gilmanli]

Using discrete components to build the circuitry has better,it is cheap and easy to find components.COLIN55 posted at 5th Augt. with two reference schematicsf,would you try it ?