Can someone help me understand how to create a meter that will allow me to read how much power I have left in a battery?

I have been getting back into RC cars and I am getting tired of just guessing how much run time I have left on my receiver pack. I would like to be able to make a meter that would be fairly small I would be able to keep inside of the car. I do not care about the numbers, I would just like to have a visual representation that would utilize one of these


That is the main goal.

However something that would be great and make my life much easier when it comes to measuing the run time left would be something that would allow me to adjust the maximum and minimum that the meter measures. This would be great because it would allow me to make as many as I want that would still work even though some receivers may be running with different amounts of cells. For example, I have a bat pack that has 5 cells (so 6v), so I would want that to be my "100% left" bar (so all bars) on the graph. And lets the receiver can run no lower that 4.5v, I would want that to be my "1% charge left" bar (so 1 bar left). However I have another reciver that runs off of 4 cells, so 4.8v, I would like to be able to make another identical meter that would be able to be set to these new numbers. So basically I would like to be able to set the "servo endpoints" except for the meter (obviously it is not a servo, that is just the reference I used)

My knowledge of electrics is very limited, but I would like to learn much more. So please do not go all out on they vocabulary because you will for sure lose me.

Thanks for your help

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There is an easier way of doing it than Frollard suggests, use an LM3914

Here is a website describing it - a lot fewer wires, and configured for what you want to do.

lemonie7 years ago
To do this, meters normally draw some power and measure the voltage. As batteries lose charge the voltage reduces a bit. To make one of these you'd need more knowledge of electronics, but here is a schematic:

En-jin lemonie7 years ago
I am the writer of this question (forgot to log in). The schematic is for a 4 led meter, If I were to want to use 10 led's (# on the bar graph). Would I have to just double the lm339 chips? And is that something that would be specific to a certain battery pack, or is it could it be used on different batteries with different voltages (basically meaning, is it adjustable.)
En-jin En-jin7 years ago
I meant use 3 chips, not double.
frollard En-jin7 years ago
I think LM339 chips can be cascaded - you just change the biasing resistors on each stage.

That circuit looks like the perfect answer to this question. A good article also.