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How to use LM3914 bar graph to indicate 7S Li-ion

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StillTrying:
Just removed the lower resistor R7 and connected R5 between BAT and pin 5.

That won't work because Vsig = Vbat = V+ = RHI

and Page 7, Common-Mode Limits says the inputs can't go within 1.4V of V+.

www.ti.com/lit/ds/symlink/lm3914.pdf

anishkgt:
The LM3914 is set up for Rlo =3V and Rhi at 4.2V. It is measuring one nominal 4V cell, hence removed R7 making the resistor divider.

In the video Dave used a 10K/10K divider as he was measuring two cell in series, ie: 6v thru 8.4v, the divider was used to drop pin#5 to 3V thru 4.2V

StillTrying:
"as he was measuring two cell in series, ie: 6v thru 8.4v, the divider was used to drop pin#5 to 3V thru 4.2V"

I'd bet his V+ was 8.4V.

anishkgt:

--- Quote from: StillTrying on April 23, 2019, 09:18:57 pm ---"as he was measuring two cell in series, ie: 6v thru 8.4v, the divider was used to drop pin#5 to 3V thru 4.2V"

I'd bet his V+ was 8.4V.

--- End quote ---
Yes he was that was why the 10k/10k voltage divider was used to drop it down for SIG(pin 5).


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StillTrying:
"10k/10k voltage divider was used to drop it down for SIG(pin 5)."

Some divider is need to keep SIG 1.4V below V+.

I changed the resistors in LTs LM3915 to work as an LM3914, and using the the values I posted in Reply#5 it's not too bad with V+ 3 to 4.2V and SIG 1.5 to 2.1V. Bottom of the plot is the 10 LED currents, they're probably too high 4 or 5mA would do.

Edity.
If I was using this to monitor 18650 charging I'd make to top 3 LEDs 4.1V, 4.2V, 4.3V, I've seen 18650 get very warm very quick at 4.3V.

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