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Simple battery charge level indicator? Answered

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I need to be able to see the charge level of a 12v rechargeable battery and want it to be as simple as possible. Would this setup work: 3 zener diodes (at different breakdown voltages 10, 11 and 12 volts for example) with cathodes connected to positive so that when the battery was above their breakdown voltage an led could light up. Here is a diagram:

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joeyc3 (author)2015-01-17

is there a simpler way to do this that only lights up a red led when charging and a green one when full?

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icengBest Answer (author)2011-08-01

Here is a fine dot battery indicator.
Leftmost RED LED is adjusted to 10 V and the
rightmost GREEN LED is 12 V giving a fractional view of
a lead acid state of charge.

A

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phantomboy (author)iceng2014-01-23

I'm tying to build a similar version of this, and was wondering how the reference voltage setup works even when v+ is variable (since battery level will be changing)? I've looked through the datasheet and still don't fully understand how the Rhi reference setup works. Thanks in advance!

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iceng (author)phantomboy2014-01-23

On the LM3914 PDF page7 see the Reference Voltage Source 1.25V is

a built in reference better then a low voltage zener found on pin_7.

Works the same way a 3 pin regulator reference like the LM317 does.

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Brose549 (author)iceng2012-06-25

Can you change this to read voltages from 11.5 vdc to 16 vdc. I will use this in my electric car project. In fact, I have 12 batteries so will probably build 12 as small as possible to measure individual batteries in my series wired battery pack. This would make a great battery pack monitor system and maybe other EV builders will use it. LED 11.5v (red) 12,12.5,13,13.5,14,14.5 (green) 15 (amber)15.5,16v (red) Thanks

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Scytheon3 (author)iceng2011-08-01

Thanks this is exactly what I was looking for

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scorpio88 (author)2012-02-09

Have you done it? did it work?

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lemonie (author)2011-07-31

You can't get (single) diodes with that much voltage drop.
You could try using transistors instead.

L

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Scytheon3 (author)lemonie2011-07-31

But you can get 10, 11 and 12 volt zener diodes which when inserted in a circuit in reverse only let voltage through after their breakdown voltage. So if the battery was flat (say 9v) then none of the diodes will allow current to pass but if it was half full (say 11 volts) then only the 10 and 11 volt diodes will conduct and so only 2 out of 3 LEDs will be lit giving a representation of battery level.

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steveastrouk (author)Scytheon32011-07-31

Yes, but you're assuming that 10V = 10V in reality etc.

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Scytheon3 (author)steveastrouk2011-07-31

OK, just as a theoretical situation then would my idea work?

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steveastrouk (author)Scytheon32011-08-01

Theoretically. Try it !

Steve

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