Battery level indicator.. (1 Viewer)

[Jay H]

I'm wondering if it is possible to build a simple battery level indicator and exactly what is measured to determine Percent Full?

I have a 6v 8ampHour NiMH battery used for my bike lights, what would a batter level indicator measure? the voltage across the terminals or something else? I can probably buy a opposite gender plug for the battery and wire it up to a analog meter and figure out the left over charge...

Would this be possible?

Jay

 

[Keith Outhouse]

Maybe something like this. You would need to measure the voltage across the battery when new and almost dead and mark the meter at those points
http://www.radioshack.com/product.as...%5Fid=22%2D410

 

[Jay H]

Well, I already have a simple multimeter with a DC Voltmeter on it, but the hard part is getting to the plus/minus of the connector. It kind of uses a phone plug but not entirely sure of the size, it's not a standard 1/8" mini phono or a full sized plug but if I could get the female connector and then solder some wires just to make it easier to probe it, that would be a start. I found some schematics online on people making 12V ones for say car batteries, but I think that using a voltmeter would serve my purpose since it's not something I would permanently connect on it. I would just connect it now and then to make sure the lights aren't almost empty.
Sometimes I can't guage length simply by time of use and when NiMH batteries die, they die FAST, they don't slowly die, they seem to go from on to off.
For example, I've biked to work all week this week, all mornings are about 15°F and I take about an hour to go to work, I don't use the lights after work because I get home before dark but going to work is before sunrise. I used it only three times this week and the battery is now uncharged. The battery was sitting around last week though fully charged and normally in normal summer temps I can go for a week and a half before I need a charge. This is sucking it dry.
But it is voltage that determines whether a battery is full or not right? That's the important part..
Jay

 

[NickSo]

I've tried playing around with batteries and a multimeter...

Im pretty sure its NOT the VOLTAGE that determines if its full or empty.

 

[Christ Reynolds]

Im pretty sure its NOT the VOLTAGE that determines if its full or empty.

thats correct, a battery that is almost dead will read the same voltage as a new one. batteries are measured in volt-amps. the voltage will always stay the same, so a voltmeter wont work as a battery tester. although i have a battery tester here, i dont really know how it works (i havent thought about how it works) but it seems to be fairly accurate.

CJ

 

[Kevin P]

The battery has to be tested under load. Hooking a voltmeter to a battery will only tell you if it's dead or nearly dead. But a voltmeter connected to the light so it's measuring the voltage while the light is on will be more accurate, though as has been mentioned before NiMH and NiCd batteries hold pretty steady and then drop suddenly. The voltage may drop slightly but then it'll just drop like a rock, at which point the battery is dead.

Cold weather has an affect on battery life, as does usage. Batteries gradually lose their ability to hold a charge, and NiCd/NiMH can exhibit a memory effect if recharged too soon or overcharged. So the shorter battery life could be attributed to these things as well, or a cell in the battery is going bad.

KJP