Confirm circuit would work

[wob_b]

Hi,
I was looking for a circuit which i could attach to a car battery and which would give me an idea of how long its going to last (its powering other things, not in a car). I found this on a website which looked perfect:

Electronics Circuit::12V Lead-Acid Battery Monitor

But looking at it now the leds are even protected with resistors. Please would someone beable to confirm wether it would actually work or not. and if not does anyone have an example of one which would?

Thank you
Rob

 

[Nigel Goodwin]

Looks a pretty standard 3914 based meter, you don't need resistors to the LED's, they are internal (or at least current sources are).

 

[audioguru]

The 47k resistor from pin 7 to ground adjusts the LED current for only 1.3mA each so they will be extremely dim.

 

[MikeMl]

Rob,

For the 12V battery in my travel trailer, I just bought an LCD Panel-mounted voltmeter. It is the kind that can read the voltage it is powered with. The meter needs a supply voltage of 5V, so I used an LM78L05 to reduce the 12V to 5V.

The intrinsic meter has a full-scale voltage of +-200mV, so I used two 1% resistors to make a voltage divider which makes the full-scale 20.00V. It has a resolution of 10mV.