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Low cost, low power battery led indication cirucit

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Vindhyachal.takniki:
1. I have a battery, a charger & a load as in ckt attached.
2. Have to glow led when charging happens. While charging current decreases while battery getting full.
Have conencted a small resistor in battery path whenever current will flow across it from charger to battrey, there will be drop across the resistor, which appears across opamp input. Since opamp  is in open loop configuration even a small drop will saturate the opanmp & will glow led.
3. Will it work as intended? Havent tried in actual yet.
4. Most of time bothe charger and battery will be connected to load, once in a month mains may go then system shifts to battery.


Probem may arrise:
1. There is small vid diff due to offsets, so opamp may be saturating even if no current is flowing, so how to avoid this situation
2. Any other low cost solution based on voltage measurements or current measurement circuit will work only?
3. Low cost is must have, low power is better if available.
4. Any other better way to do that with/without cost constraints.

VEGETA:
You have to see your opamp capabilities, like it may not be able to drive 2.2k ohm connected to an LED. Maybe 100 ohms is enough.

In your circuit, the LED will always be on (assuming op-amp specs are good) until the battery is fully charged or until voltage difference is beyond the capabilities of the op-amp.

mikerj:
No, it won't work.  You are attempting to use the input offset voltage of an op-amp as a voltage reference, but the offset voltage is not a well defined or controlled parameter; it can vary in both magnitude and polarity across parts and over temperature.  If you build enough devices a few may work well enough over a limited temperature range, some will never switch off the LED or may switch it off prematurely.  Even if you hand picked a device with a suitable offset at room temperature, without any hysteresis the LED will flicker as the current approaches the switching point.

Additionally for switching applications rather than linear operations, you should be looking at comparators rather than op-amps.

Jwillis:
Simple low cost , low voltage indicator for 12V.Can be adapted for any voltage by changing diode values.
With this circuit the LED remains off when the voltage is above  approximately 11V and turns on below approximately 11V.
Use across your battery terminals .
If you want it go turn on at around 8V use 5.1 Zeners.

TerminalJack505:
Here's a circuit that can be made with jellybean parts and will, in theory, detect when a small current is flowing into the battery.  The P-channel MOSFET can be pretty much any part.

The gain can be adjusted by changing the values of R1, R2, and R3.  As shown it has a gain of 510 which should illuminate the LED when about 5mA of current is flowing into the battery.

This seems to work in the simulator but I can't really say how well it would work in real life.  It's something you would want to prove-out on a breadboard, obviously.

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