Two-Transistor version of Daftmike's low-battery Indicator

[Mario]

I designed this circuit based on Daftmike's low-battery indicator circuit. If you're thinking of using his low-battery indicator and don't mind giving up the green LED in exchange for some parts savings, use this one.

All the info is right there. This circuit uses only two transistors as opposed to five. This saves you some parts and space as well as a bit of battery life. I took out the green LED. So, there is no indicator when the battery is OK but the LED turns on once it goes below the set voltage.

Here is his original thread:
viewtopic.php?f=7&t=255

 

[seanmacdonn]

Nice job. I might use this.
EDT: is there a way to convert it to a CMB by making batteries stop charging when it hits a certain voltage? I read about it somewhere online, but I didn't understand it very well. This would (I think) allow charge and play, depending on what power supply you use. It's easier to get a hold of a 2A 7.4V power supply than a 2A 7.4V smart charger (I've only found up to 1.5A), and It's cheaper too ($50 vs $8.95)

 

[Mario]

I combined this circuit with this alkaline battery charger:
http://www.afrotechmods.com/reallycheap ... /batts.htm

It stops charging when the battery is full. But, I would not try it with li-ion. They're just too sensitive. I probably wouldn't try it with anything other than alkalines, actually.

 

[seanmacdonn]

so couldnt you hypathetically make a low battery indicator that turns red about when its three quarters empty, and shuts off at another point? not having anything to do with recharging.

 

[Mario]

I suppose you could. You could also try simply putting two of these in, both set at different voltages.

Updated first post with better diagram.

 

[jelte1234]

would this work like a nice battery bar? ( only as an example, the resistors aren't calculated)

Jelte1234

 

[thecasperrojas]

Re: Two-Transistor version of Daftmike's low-battery Indicat

ok i want to use this for 7.4v li-on battries but am lost in what resistens i need in the R4 so the led will turn on in 7.2v

 

[Ashen]

Re: Two-Transistor version of Daftmike's low-battery Indicat

The adjustable resistor is for the led, based on its specs. The trimpot adjusts the voltage that it will turn on according to.

 

[thecasperrojas]

Re: Two-Transistor version of Daftmike's low-battery Indicat

thanks got it working

 

[thecasperrojas]

Re: Two-Transistor version of Daftmike's low-battery Indicat

@Ashen: oh man got it working but only 5 min before it turns off ,i want it to activate 20 min before runing out can you tell what values do you use

 

[Prog]

Re: Two-Transistor version of Daftmike's low-battery Indicat

Adjust the trimpot.

 

[thecasperrojas]

Re: Two-Transistor version of Daftmike's low-battery Indicat

thanks got it to 10 min but thats pretty good for me