DC Voltage indicator

[Don Wright]

I'm looking for an indicator lamp that will indicate when a battery voltage drops below a certain voltage setpoint (i.e. 10 volts). I need to keep some engine electronics alive during transport of an engine with a battery and need an indicator that is green, or steady, or something when the voltage of the battery is above the setpoint, put changes to red, or flashes, or something when the voltage drops below the setpoint to alert someone to throw a charger onto the battery.

Anybody have any ideas? We found one, but the green color was so dim, you couldn't really tell it was on unless you were looking right over it...not good for a test cell.

Thanks. I know this isn't FIRST related, but I hoping someone here can help...

[mechanicalbrain]

Now this is probabely me being crazy but you might want to google DC voltage indicator . The first result was this http://www.gibsonteched.com/ck005.html .

[BrianBSL]

Are you looking to buy one, or is building one an option?

My knowledge of electronics is far more limited than I would like it to be, but what I would probably do is use a regulator to get you a fixed 5V value, and then use a comparator with your 5V reference and a resistor voltage divider on a line coming off the battery, if the 5V line is higher then the battery is below your value, and if its lower, then the battery is still good.

[Mike Betts]

I agree with Brian. Building is better. A resistor divider as the - input to a comparitor (LM211?) IC and a zener diode as the + input with an LED on the output should work fine.

[Al Skierkiewicz]

Don,
Maxim has a line of battery monitor ICs and they are available from Digikey. A simple LED will not give the indication you are looking for without additional circuitry.

[Don Wright]

Thanks for the help guys.

Designing and building one is an option, but only if I can't find an already designed solution. There are a lot of voltage level IC's out there and "kit" solutions, but it needs to be a very complete and robust solution. It will be living in a test cell environment and needs to be very reliable. So, it would require circuit board design, prototyping, beta units, final production...all things I would like to avoid due to costs and time.

I know it requires more than just a simple LED, but I didn't know if anybody here had any experience with something that already exists. The unit we found was a nice large LED, housing made of machined aluminum, with simple jumpers on the back to select the voltage level, and small terminals for connecting wires. It is very nice, and cheap (<$40), but just is not bright enough. We are in discussions with the supplier to try and recitify, but I'm just trying to find other options to fall back on.

And mechanicalbrain, I've googled everything I could think of believe me. The circuit you show would not work because it would require modifications for panel mounting in the box... Thanks for the suggestion though.

Thanks again for the help everyone... I appreciate it...