Electronics > Beginners
How to use LM3914 bar graph to indicate 7S Li-ion
<< < (4/4)
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).


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s

Sent from my iPhone using Tapatalk
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.
Navigation
Message Index
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod