help needed in lm3914 circuit design

[hansika]

Hi every one,
i want to monitor the health status of 24V battery using LM3914 IC, i am new to this type of work, what my doubt is can we monitor the 24V battery health status using this IC , can any one please explain how it will work and how many ICs i need for this requirement,thanks in advance.

 

[ericgibbs]

Hi every one,
i want to monitor the health status of 24V battery using LM3914 IC, i am new to this type of work, what my doubt is can we monitor the 24V battery health status using this IC , can any one please explain how it will work and how many ICs i need for this requirement,thanks in advance.

hi,
To monitor a 24V battery, its possible to make a resistive potential divider to reduce the 24V to 12V.
This 12V is connected to the input of the LM3914
The LM3914 is set up to display from say 10V thru 15V in 0.5V increments, so the 24V is displayed as 20V thru 30V.

Do you follow OK.?
Look here: https://www.electro-tech-online.com/blogs/ericgibbs/136-single-dual-lm3914-v3-0-calculator.html

 

[hansika]

Thank you for your quick reply i have few more doubts here when i change the signal input then only led status is changing(observed in the link given by you) when i see the data sheet of LM3914 the signal input range is only 0-5V but i need to monitor 12V so can you explain me some datails how this will operate thanks in advance.

 

[ericgibbs]

Thank you for your quick reply i have few more doubts here when i change the signal input then only led status is changing(observed in the link given by you) when i see the data sheet of LM3914 the signal input range is only 0-5V but i need to monitor 12V so can you explain me some datails how this will operate thanks in advance.

hi,
Consider the battery is at 24V, so if I have a resistor divider of two, 10K's and I connect this divider across the 24V battery I will have 12V at the junction of the two 10K resistors.
So if the 24V battery voltage falls to 22V, at the divider I will have 11V.

If the junction of the divider is connected to a LM3914 input and the Vlow of the LM3914 is set to 10V and the Vhi is set to 15V, then the LM3914 LED's will show voltages from 10V thru 15V, which corresponds to a battery voltage of 20V thru 30V, in 1Volt steps/LED.

Do you follow OK.?

 

[hansika]

hello sir,
while i am designing the circuit in proteus software i am getting some doubts, i am giving signal input as 10 to 15V as you said and as of now i am giving 10V and 15V supply from a DC battery in proteus at Vext low and Vext high pins, and i am connected 5V supply at V+ and mode pins what my doubt is what about refout and ref adj pin connections, when i am connecting refout to 3.5K with 9K and adj pin to junction of 3.5K and 9k(as shown in the above exe file) what happen is when i am grounding the 9k no led is glowing but when i am leave the 9k as floating(no ground and no supply) it is working fine , why this is happening.

 

[ericgibbs]

hello sir,
while i am designing the circuit in proteus software i am getting some doubts, i am giving signal input as 10 to 15V as you said and as of now i am giving 10V and 15V supply from a DC battery in proteus at Vext low and Vext high pins, and i am connected 5V supply at V+ and mode pins what my doubt is what about refout and ref adj pin connections, when i am connecting refout to 3.5K with 9K and adj pin to junction of 3.5K and 9k(as shown in the above exe file) what happen is when i am grounding the 9k no led is glowing but when i am leave the 9k as floating(no ground and no supply) it is working fine , why this is happening.

hi,
If you could post a sketch of your circuit, showing also the voltages it would be helpful.

It sounds as though you are connecting the incorrect voltages to the LM3914.?

 

[hansika]

sorry sir my proteus is not properly installed thats why i am unable to post the circuit, i have drawn the circuit in word, please see this and tell me where i am doing wrong

 

[ericgibbs]

i have drawn the circuit in word because my proteus is not working properly below is my circuit
**broken link removed**

and LEDs positive is connected to 5V and negative is connected to remaining pins in LM3914. when the 9KOhm shown in fig is grounded the circuit is not working properly when it is floating then the circuit working fine. please clarify these doubts

hi,
Have tried your link, all I get is page not found.???

 

[hansika]

sorry sorry i think now you can see it now ........ please tell me where i am doing wrong

 

[ericgibbs]

sorry sorry i think now you can see it now ........ please tell me where i am doing wrong

ok, I see it now.
You should have the +V & Mode to LM3914 at 15v, keep the Vled at +5V
Try that and let me know what you get, I do not use Proteus so I cannot tell you if what you are getting is accurate.

 

[hansika]

ya now i am connected V+ and mode pins to +15V , same result is coming if i am connect 9K ohm resistor to Gnd nothing is coming(No led is glowing) and when the 9K is left without any connection(floating) then the result is coming as expected

 

[hansika]

what is the purpose of Refout and Refadj in LM3914 circuit

 

[ericgibbs]

what is the purpose of Refout and Refadj in LM3914 circuit

hi,
The Reference Voltage Out is the voltage which is used internally for the 10 comparators, the Reference Voltage Adjust is used to SET the Reference Voltage out, also the current flowing in the resistor between RefOut and RefAdj sets the LED current.
The LED current is approx 10 times greater than the resistor current.

I will try your circuit in a 'real' LM3914 IC, let you know what I find.

 

[hansika]

k thanks in advance, awaiting for your reply.

 

[ericgibbs]

k thanks in advance, awaiting for your reply.

hi,
Little late but I have to eat...

Completed the hardware test of the LM3914, the +V to the LM3914 MUST be at least 2 volts higher than the RefHi volts of +15V, so I have use +18V for the +V.
Keep the Vled at +5V, if you are using only one LED per pin.

It works OK, from +10.5V thru 15V [battery voltage displayed OK]
Do you follow OK.?

 

[hansika]

k but we are giving 18V to V+ which is maximum value to that pin can't it will effect the IC for longterm purposes? ,so as per your suggestions below one is the final circuit or if you make any changes can you please post that circuit diagram.

 

[ericgibbs]

k but we are giving 18V to V+ which is maximum value to that pin can't it will effect the IC for longterm purposes? ,so as per your suggestions below one is the final circuit or if you make any changes can you please post that circuit diagram.

hi,
A supply of 18V is not the maximum supply voltage allowed, the absolute Vmax is 25V, I have used LM3914 with +20V for a number of projects, with no problems.

I will look thru your circuit.

 

[ericgibbs]

hi,
Look at these images.
This circuit has been built on a project board and is working as expected.

 

[hansika]

Thank you for your guidance, i want some guidance in dspic serial programming in mikroC IDE ,if you can help me please let me know so that i can know so many new things from a expert like you

 

[ericgibbs]

Thank you for your guidance, i want some guidance in dspic serial programming in mikroC IDE ,if you can help me please let me know so that i can know so many new things from a expert like you

hi,
I am sorry I dont use mikroC and dsPIC's, I know there are lots of members who do..
I would suggest you start a new thread in the micro-controllers Forum.