hi all. after browsing for a bit and not finding anything that actualy works, can somes kindly share a schematic of how to configure the 3914 to monitor the voltage of a single cell lithium battery, so from 3v to 4.2v?

any help would be greatly apreciated

steve

 

12V battery monitor
another one
more
AllAboutCircuits

 

12V battery monitor
another one
more
AllAboutCircuits

Hi.
Thanks. But non of these answer my question. Non apart from the last one are
About the voltages I need to measure. And the last one I have read and there is no actual schematic they agree on that works.
Steve

 

There are two pins, RHI and RLO which set the voltages on each end of the string of 1k resistors inside the IC.
There are formulas in the data sheet showing how to set the two voltages.
Work out the math so RHI=highest voltage on the battery and RLO for the lowest voltage you will allow. Might use a resistor + TL431 to get a higher voltage for RHI.
RHI=full battery, RLO=empty battery.
In many examples they can't get RHI at the right voltage. In some of the battery monitoring examples they use two resistors to divide down the battery voltage to a lower level. (SIG IN)

You can connect RHI to 1.25V REF OUT. Put a 10k POT under RLO to raise its voltage. Put a 100k pot from +Battery to ground. Set the battery-pot so a fully charged battery just lights the top LED. Set the RLO POT to light the bottom LED when the battery voltage is low.

 

R2 sets the brightness of the LEDs.
R1 sets the voltage for the bottom LED.
R3/VR1 divides down the battery voltage so the voltage at SIG-IN is at 1.25V when the battery is very full.
With RHI connected to 1.25V from OUT the top LED is set for about 1.25V.
S1 sets bar or dot mode.

The IC should work down to 3V supply so it will run off the battery under test. (do not use white LEDs, their voltage is about 3V, use low voltage LEDs)
With the battery range 4.2 to 3.0 was divided by 3.3 by VR1 you get a range of 1.25 to 0.9. The top LED responds in the 1.25 range which is 4.2 on the battery. Now we need to set R1 so there is 0.9V across it.

 

Hello,

See below.
Each LED gets about 3mA. You'll have to adjust P1 so LED at pin 10 turns on at 4.2v

eT

 

See below.

Good job. Please post your spice files. Thanks RonS.

 

you sir are awesome. finaly someone who can show a circuit that actually works. thanks so much
my only issue is (not your fault) my led 1 lights up very faint no matter where the voltage is. any idea why this is? when it gets to 3v it lights up fully. but anywhere above this it lights up very dim when it should in fact be off? cheers

 

Good job. Please post your spice files. Thanks RonS.

Thanks Ron.

Attached is spice files.

eT

 

you sir are awesome. finaly someone who can show a circuit that actually works. thanks so much
my only issue is (not your fault) my led 1 lights up very faint no matter where the voltage is. any idea why this is? when it gets to 3v it lights up fully. but anywhere above this it lights up very dim when it should in fact be off? cheers

Hello,

Pin 1 always has a constant current of 100uA. Its used for "carry" when cascading multiple LM3914.
See excerpt from datasheet below.



eT

 

Hello,

Pin 1 always has a constant current of 100uA. Its used for "carry" when cascading multiple LM3914.
See excerpt from datasheet below.

View attachment 198239

eT

awesome thanks, although im confused as to where led 11 is meant to be?

is it easy for me to change it from 3v low end to 3.2v? am i right in saying i will need to adjust R1 (make it a larger value) to get the desired effect?

cheers

steve

 

awesome thanks, although im confused as to where led 11 is meant to be?

Pin 11 is on the second LM3914 when two or more devices are being cascaded. There is an example on the datasheet.
Pin 1 on first device is connected to pin 11 of the second device.

is it easy for me to change it from 3v low end to 3.2v? am i right in saying i will need to adjust R1 (make it a larger value) to get the desired effect?

cheers

steve

I'm not clear on the effect your trying to achieve(?)
You mean eliminate the glow on pin 1 when off? If so, you might try shunting LED 1 with a 10k resistor.

eT

 

Pin 11 is on the second LM3914 when two or more devices are being cascaded. There is an example on the datasheet.
Pin 1 on first device is connected to pin 11 of the second device.



I'm not clear on the effect your trying to achieve(?)
You mean eliminate the glow on pin 1 when off? If so, you might try shunting LED 1 with a 10k resistor.

eT

Hi

thanks for the reply.

i assumed pin 1 was meant to have the 10k accross it, i tried this and it no longer issuminates. so thanks again for the info.

ref the other part, i was refuring to adjuting the low end led, so instead of it lighting up from 3-4.2 volts, would i need to adjust R1 to make it go from 3.2-4.2v?




steve

 

Hi

thanks for the reply.

i assumed pin 1 was meant to have the 10k accross it, i tried this and it no longer issuminates. so thanks again for the info.

ref the other part, i was refuring to adjuting the low end led, so instead of it lighting up from 3-4.2 volts, would i need to adjust R1 to make it go from 3.2-4.2v?




steve

Try changing R3 to 38K.

eT