I've been searching for a few days now and can't seem to find anything that may work. I need a low battery indicator (that draws very little power) for a circuit I am using. The battery bank I expect to peak out around 18 volts or there abouts, and eventually decrease to about 6 volts before my peripheral devices crap out. So, does anyone have any idea how to make a low cost, simple low battery monitor that can be powered from unregulated source that will swing between a minimum of 6 volts to a max of around 18 volts?

I would like it to light a red led when source voltage drops below around 8 or 9 volts, so I guess something adjustable would be great (or how to calculate voltage sets). Also, I would like a green led to be a part of the circuit for anything above 8 or 9 volts but not lit 100% of the time, maybe a pushbutton could be incorporated to at least show that it is still above 8 or 9 volts as the led constantly on will only pull power.

Anyone with a schematic? Thanks for the help.

 

An LM10 has an opamp that can be used as a comparator and has a precision adjustable voltage reference.
Its minimum supply voltage is 1.1V and its maximum is 40V. Its current is only 270uA.
It is in an 8-pins DIL case.

 

An LM10 has an opamp that can be used as a comparator and has a precision adjustable voltage reference.
Its minimum supply voltage is 1.1V and its maximum is 40V. Its current is only 270uA.
It is in an 8-pins DIL case.

Would you by any chance have a schematic? Thanks.

 

Here is the schematic for an LM10 to make its output go low when the battery voltage drops to 6V or less:

 

Do you have a figure for maximum current consumption with no LEDs lit?

Search Digikey or Mouser for comparators with a built-in reference. There are many low-power options from companies like Maxim and Linear Technology. There may be a problem with that high maximum supply voltage; you may need a low-current regulator (again search on Digikey or Mouser). It's a tradeoff between simplicity / low cost, and low current.

Hewlett-Packard (now Avago) make some high-efficiency red LEDs - HLMP-D150 and HLMP-K150 I think. These glow quite brightly at only 1 mA. Their green ones aren't as efficient though.