"high" or "low" voltage battery monitor parts: U1 LM741 op amp IC R1 100k ohm potentiometer R2, R3 10k ohm resistor R4 330 ohm resistor LED1 light emitting diode all resistors are 5 or 10 percent tolerance, 1/4-watt R1 controls the trip-point of the circuit. adjust it accordingly. to reverse the logic (have the led light up when the battery has at least X amount of power,) connect the led to ground through R4. http://www.reconnsworld.com/forum/read.php?14,4,4#msg-4 Sat, 25 May 2013 13:26:13 -0400 Phorum 5.2.9a http://www.reconnsworld.com/forum/read.php?14,4,208#msg-208 Re: "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,208#msg-208 can you tell me values for 6 volt?]]> eeko Battery Power Monitors Thu, 29 Jul 2004 08:53:10 -0400 http://www.reconnsworld.com/forum/read.php?14,4,142#msg-142 Re: "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,142#msg-142
Quote

(andrew @ June 27 2003,02:28):


parts:
U1 LM741 op amp IC
R1 100k ohm potentiometer
R2, R3 10k ohm resistor
R4 330 ohm resistor
LED1 light emitting diode

all resistors are 5 or 10 percent tolerance, 1/4-watt
R1 controls the trip-point of the circuit. adjust it accordingly. to reverse the logic (have the led light up when the battery has at least X amount of power,) connect the led to ground through R4.


This circuit doesn't work.

Try this one. Zener diode for 12V battery is 11V, threshold is 11,7V. LD1 light when voltage drops under threshold voltage, threshold voltage is zener voltage + 0,7V
For another threshold voltage use another zener diode.]]> reber Battery Power Monitors Tue, 20 Jan 2004 08:31:16 -0500 http://www.reconnsworld.com/forum/read.php?14,4,134#msg-134 Re: "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,134#msg-134 MP]]> MP Battery Power Monitors Mon, 22 Dec 2003 10:41:56 -0500 http://www.reconnsworld.com/forum/read.php?14,4,127#msg-127 Re: "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,127#msg-127 conducts.

See, what Peter's saying is that both + and - of the opamp are on the (variable because it's a battery) 12V, so readings won't be accurate. You need a steady reference (-, pin 2).

He suggests a zener instead of R2, which will hold pin 2 at 6V, even as the battery runs down. So by referencing this lower fixed voltage (6V) to the battery coming down from 12V, we know when its discharging. Circuit will fail below 6V tho, which is OK.

Only thing is, Peter suggests hysteresis (a good idea, to stabilize) on pin 3, whereas it should instead go a 10K from pin 6 to pin 2. No biggie.

I am grateful to Peter for this idea, because my Vcc is 5V, but I must measure a signal of 6-8V. So I will put a 6V zener where he suggests, and a resistor divider on pin 3 instead of the pot, to make a difference opamp. Hopefully it will then take the difference between6V, and 6-8 on pin 3, which theoretically will be 0-2V. Only thing I'm worried about is temperature drift, as mine will be an outdoor device.

Wish Peter or anyone could comment?]]> rooter Battery Power Monitors Sat, 06 Dec 2003 19:17:50 -0500 http://www.reconnsworld.com/forum/read.php?14,4,105#msg-105 Re: "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,105#msg-105 violet Battery Power Monitors Mon, 17 Nov 2003 21:50:21 -0500 http://www.reconnsworld.com/forum/read.php?14,4,98#msg-98 Re: "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,98#msg-98
Quote

(andrew @ June 26 2003,21:28):


parts:
U1 LM741 op amp IC
R1 100k ohm potentiometer
R2, R3 10k ohm resistor
R4 330 ohm resistor
LED1 light emitting diode

all resistors are 5 or 10 percent tolerance, 1/4-watt
R1 controls the trip-point of the circuit. adjust it accordingly. to reverse the logic (have the led light up when the battery has at least X amount of power,) connect the led to ground through R4.

OOPS! Nice idea but you have two variables feeding your op amp. Make one fixed by replacing the lower resistor of the voltage divider with a zener or programmable zener TL431 set to 6 volts or so and the squircuit will work fine. Zener diodes need a minimum current and their zener voltage may vary with supply voltage and temperature. The TL431 or equiv are easily "programmed" with two resistors. Data available from Texas Instruments and many other places on the web. If you want to add hysterisis, add a 470K resistor between pin 6 and pin three. You may need to experiment with the exact value to get the desired offset (try a 1 meg pot first).]]> Peter Battery Power Monitors Tue, 14 Oct 2003 04:52:25 -0400 http://www.reconnsworld.com/forum/read.php?14,4,4#msg-4 "high" or "low" voltage battery monitor http://www.reconnsworld.com/forum/read.php?14,4,4#msg-4

parts:
U1 LM741 op amp IC
R1 100k ohm potentiometer
R2, R3 10k ohm resistor
R4 330 ohm resistor
LED1 light emitting diode

all resistors are 5 or 10 percent tolerance, 1/4-watt
R1 controls the trip-point of the circuit. adjust it accordingly. to reverse the logic (have the led light up when the battery has at least X amount of power,) connect the led to ground through R4.]]> andrew Battery Power Monitors Thu, 26 Jun 2003 21:28:14 -0400