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# how can i adjust thi charger circuit to fully charge battery with light up LED at 1.3

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#### tengyy

##### Member level 1

one NiMH 1.2V cannot light up the LED1, i think that is due to insufficient current. but with two 1.2VNimh battery can light up.

So, how can i adjust the resistance value in order to light up the LED1, or how to increase current in the LED 1 way when i plug in one NImh battery?

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k... solve it... jst adjust the value of R1.... but still under investigate wat value suitable for it...

R4 needs to be reduced to increase the brightness of the LED when two batteries are being charged.
With only one battery ( 1.2V) there will never be enough voltage to switch on a LED which will need more then 1.7V (special type) or 2.2 V general purpose type.
Frank

tengyy

### tengyy

Points: 2
LED1 is "stupid" and simply lights when the circuit is powered and its output is not shorted. LED2 lights all the time the circuit is powered and even lights if the output is shorted.
The LED does not only light when the battery is fully charged.

RV1 adjusts the maximum output voltage. One fully charged Ni-MH cell is 1.35V if charged from a low current and is 1.5V when charged from a high current. I charged my Ni-MH cells 2 weeks ago to 1.45V and today without a load they all measure 1.35V.

A Ni-MH battery charger IC detects the slight rise then drop in voltage that occurs when a cell becomes fully charged then shuts of the charging and turns on the LED that indicates the charging is finished.
Here is a graph of the voltage of a Ni-MH cell being charged a various currents. See the slight rise then drop in voltage when it becomes fully charged:

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tengyy

### tengyy

Points: 2
R4 needs to be reduced to increase the brightness of the LED when two batteries are being charged.
With only one battery ( 1.2V) there will never be enough voltage to switch on a LED which will need more then 1.7V (special type) or 2.2 V general purpose type.
Frank

Actually, after pass through the LM317T, the output for LED1 around 2.5V, but after assembly the battery, the voltage across LED1 become 0, and the open circuit part of battery is around 3.5V...

RV1 adjusts the maximum output voltage. The values shown result in a minimum of 4.79V when RV1 is shorted and the maximum voltage is 8.63V.
The voltage across LED1 will never be 0V because the minimum output of an LM317 is 1.25V.

RV1 adjusts the maximum output voltage. The values shown result in a minimum of 4.79V when RV1 is shorted and the maximum voltage is 8.63V.
The voltage across LED1 will never be 0V because the minimum output of an LM317 is 1.25V.

I advised tengyy to replace the 0.5 ohm with a link, if he did that then he will get 0V on the LED when the cell is s/c.

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Of course the output voltage and the voltage to LED1 is 0V when the output is shorted. But the output is not supposed to be shorted.

View attachment 117004

one NiMH 1.2V cannot light up the LED1, i think that is due to insufficient current. but with two 1.2VNimh battery can light up.

So, how can i adjust the resistance value in order to light up the LED1, or how to increase current in the LED 1 way when i plug in one NImh battery?

- - - Updated - - -

k... solve it... jst adjust the value of R1.... but still under investigate wat value suitable for it...

Do you want CV mode to turn on LED or when CV mode drops to below 10% current?
If so ,then detect that with a comparator across Rcl with threshold =0.07V and use open collector to shunt LED2 via a smaller equivalent R value. Swap LED colours so Green is on output and thus 3.3V/6.6mA= ~470 Ohm or less. between open collector and LED2 Anode.(+)

It works.. gauranteed

Simple modification only with open collector comparator

Red = ON with no battery or CC complete and now CV mode
Red= OFF = CC mode

Green = ON CHarge complete or no battery

Obviously there is no faulty battery test in this simple design, except if you find it charges too fast, you know it is bad.

With another simple modification you can makeit work properly with Red= charging and Green = charge complete or no battery, can you guess what it is?

Any questions?>

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