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

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anishkgt:
Hello All,

I have the attached schematic please advise the correct way to wire these up to indicate the voltage of each cell. The voltage is 7 cells in series at 4.2v and the lower voltage is 3 and highest is 4.2. I saw Dave's video on how he uses the IC with 8.4v but i did not know how it would be in a 7 cell configuration.

Audioguru:
You might be too late because the LM3914 in the DIP through holes package is obsolete and not available anymore. Tiny surface-mount ones are still made and available if you can use them. The datasheet explains how to calculate and wire resistors to show the voltage range you want but I am sorry that I am too busy to do it for you.

If you use surface-mount ICs then calculate that they do not overheat if you use them in the bar mode, they will be much cooler in the dot mode.

anishkgt:

--- Quote from: Audioguru on April 19, 2019, 07:46:56 pm ---You might be too late because the LM3914 in the DIP through holes package is obsolete and not available anymore. Tiny surface-mount ones are still made and available if you can use them. The datasheet explains how to calculate and wire resistors to show the voltage range you want but I am sorry that I am too busy to do it for you.

If you use surface-mount ICs then calculate that they do not overheat if you use them in the bar mode, they will be much cooler in the dot mode.

--- End quote ---
Thank you for the comments. Still searching for the values of the resistors.


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Equipments: DSO104z, Hakko FX888D, Brymen BM869s

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StillTrying:
"lower voltage is 3 and highest is 4.2."

As you're dividing the cell voltage by 2 with the 10ks, SIG will be 3V/2 to 4.2V/2, so you need to arrange RLO = 1.5V and RHI = 2.1V.

anishkgt:

--- Quote from: StillTrying on April 20, 2019, 09:52:53 am ---"lower voltage is 3 and highest is 4.2."

As you're dividing the cell voltage by 2 with the 10ks, SIG will be 3V/2 to 4.2V/2, so you need to arrange RLO = 1.5V and RHI = 2.1V.

--- End quote ---
Thanks

My battery voltage is 7s. So is there is max voltage that the SIG can withstand.
I need keep my RHI = 4.2v and RLO = 3. So in a 7s that would translate as 29.4v and 21v.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s

Sent from my iPhone using Tapatalk

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