Hey guys,

I'm in need of an 8.4v battery monitor circuit, using a LM3914 from National. The battery is NiMH (though it shouldn't make a difference...).

Also, if I wanted to change the battery from 8.4v to 7.2v, what would I have to change on the diagram (I'm guessing some resistor values)?

How would I calculate the resistor values if I wanted the circuit to monitor a different size battery?

Thanks in advanced!

-Skyone

 

I just posted one on another forum for a lead-acid. The monitor had a range of 11.8 to 13.8V. I could change it for you if you tell me the range you want to cover.

__________________
Ron

 

Atleast a 7.2v-8.4v would be awesome, maybe 7.2-9.6v, if it's not any trouble.

Thanks again!

 

Do you mean you want it to be adjustable? Keep in mind that the high end indicates fully charged, and the low end means you need to recharge.

__________________
Ron

 

It would be nice to be adjustable, yes.

 

Sorry for the BUMP, but I still need such a diagram. Ron, can you help?

 

Each fully charged cell is about 1.5V fresh from the charger. Then an 8.4V battery with 7 cells will be 10.5V.

Each discharged cell will be about 1.0V. Then a 7.2V battery with 6 cells will be 6.0V.

Do you want the voltmeter to accurately show this entire range?

__________________
Uncle $crooge

 

Yeah, Skyone, you need to specify the adjustment range and the full-scale range(s).

__________________
Ron

 

Ok, I need a 7 Cell (8v-10.5v) battery monitor. I have no more need for the 6 Cell 7.2v one. Does this help?

EDIT: Meaning that it doesn't need to be adjustable, just set to measure a regular 8.4 NiMH battery.

 

I think the schematic is on my home computer. I'll look for it when I get home.

__________________
Ron

 

Thanks man, you guys are awesome.

 

Skyone, what are you going to use as a power supply for this monitor?

__________________
Ron

 

What does the power supply's voltage have to be? I would like to use the battery I'm monitoring as a supply, with a voltage regulator to cut down the voltage to however much the 3194 needs.

Thanks!

 

OK, here's the schematic. I haven't tested it, or even simulated it, but I think it will work.

Attached Images

expanded scale battery monitor.PNG (25.1 KB, 101 views)

__________________
Ron

 

Thanks, Ron.

The only thing I'm confused on is the TL071 (U2). What are the pins that are shown in the schematic? I'm guessing IN+, IN-, OFFSET 1 and OFFSET 2, while OFFSET 2 is attached to GND? Or is IN- attached to GND? Also, on R5, and R8 - are those linear pots?

EDIT: What do the LEDs have to be rated at, in voltage?

-Thanks!