# FULL SIMPLER BATTERY INDICATOR WITH LEDS

Joined May 4, 2020
78
I am having a 7.6v chargeable battery. I am charging the battery direct with 9v charger but it might over charge the battery. Is there a way can I do this with (Bi-colour LED) or 2 LEDs one red for charging and green for full, with 7.1v zener diode. How can I connect this pieces of electronic components?

#### AlbertHall

Joined Jun 4, 2014
11,155
You connect the 9V supply to the battery. The green LED comes on. <time passes> The battery reaches its full charge voltage and the red light comes on. From then until you notice that the red LED has come on the battery is being overcharged.

Use the proper charger for whatever chemistry this battery is.

Joined May 4, 2020
78
The aim is simple bi-colour indicator without an integrated circuit. I am having a shaving machine which is charged by 4.4v charger but the li-lion battery in there is just 2.4v, there is only one red LED for charging and no full indicator LED. I think the charger is only 9v when is not loaded.

#### AlbertHall

Joined Jun 4, 2014
11,155
I am having a shaving machine which is charged by 4.4v charger but the li-lion battery in there is just 2.4v
So where did "I am having a 7.6v chargeable battery. " come from?

Joined May 4, 2020
78
if you are having 7.6v battery you dont charger it with exactly 7.6v charger. 9v charger is okay. what I want is full battrey indicator

#### crutschow

Joined Mar 14, 2008
26,829
if you are having 7.6v battery you dont charger it with exactly 7.6v charger. 9v charger is okay. what I want is full battrey indicator
Still doesn't explain why you talk about a 2.4V battery in post #3.

The simplest circuit to accurately turn on an LED when the voltage becomes high is with a TLV431 inexpensive programmable reference as a comparator.

LTspice simulation of example circuit below:
The LED switches when the Ref voltage crosses 1.24V as determined by the R2 - R3 voltage divider.
The values shown give a Vb switch point of 7.6V.
Those values can be changed to give the trip point you want.

#### KeithWalker

Joined Jul 10, 2017
1,600
7.6 volts is the nominal voltage of two general purpose Li-ion cells connected in series. The actual voltage can range between 8.4V(4.2V per cell fully charged) and 6V (3V per cell discharged). If you continue to charge the cells past the 4.2 volts per cell cutoff, you will drastically shorten the life of the cells. A 9V charger will do that! If the voltage across one cell drops below 2.7V, it will become permanently damaged.
The correct way to charge a Li-ion battery is by limiting the current to about 3.7C (C is the battery capacity in mAH ) until the voltage reaches 4.2 volts per cell and then maintaining that voltage until the current drops to 10% of the initial charge current. If you charge it any other way you will either not fully charge it or you will permanently damage it.
Regards,
Keith

#### Tonyr1084

Joined Sep 24, 2015
5,830
When I was a kid we went visiting out of state. One person we visited had a flash light that could be plugged into the house outlet to charge it. The warning was not to overcharge it otherwise it would cease to function. Well, I was mesmerized by such a flash light. The person we were visiting bought one for me and presented it as a gift. When we returned home I promptly plugged it in to charge it. Then I forgot about it. Then it didn't work.

OK, you're not a child. But my concern would be two fold: First, Li-ion batteries require a limited current for charging. And that current changes during different states of charge. It's not simply linear, it's more of a two level charge current. Now, I'm certainly not the expert on Li-ion's, but the second issue that becomes a concern is that if improperly charged they can become serious fire hazards. Simply applying a voltage higher than the battery's rating can be dangerous IF certain batteries are being charged. And given MY propensity for forgetting things - I'd be homeless if I tried what you want to do.

Battery chemistry is important. If we were talking about a lead acid battery - that's an entirely different story. Give them an available 14.4V DC and they will take a charge until they are fully charged. Their current will depend on the battery itself. But Li-ion's can bite.

#### Alec_t

Joined Sep 17, 2013
11,984
the li-lion battery in there is just 2.4v
Are you sure it's a Li-ion cell? The normal cell voltage is 3.7V nominal.

#### Tonyr1084

Joined Sep 24, 2015
5,830
I am having a 7.6v chargeable battery.
7.6 volts is the nominal voltage of two general purpose Li-ion cells connected in series.
I am having a shaving machine which is charged by 4.4v charger but the li-lion battery in there is just 2.4v
At this point we don't know what you have. IF you are charging via 4.4V, I have an old shaver that has two Nickel Metal Hydride batteries that are charged from a charger with an unloaded voltage output of 9 volts. Sounds similar to what you have. These batteries, the ones I have, also have a charge control board. Meaning they can not be over charged, nor can they be overly drained. The circuitry is far from "simple".

Joined May 4, 2020
78
Thanks crutschow for the TLV431 reference as a comparator, and thanks all for your advises. But the subject was full battery LED indicator, not technical types of batteries!

Joined May 4, 2020
78
shaving machine which is charged by 4.4v charger but the li-lion battery in there is just 2.4v was another example, the 7,6v li-lion battery and 9v charger is a complete device manufactured. what I wanted is only to add LED to show full battery, nothing improvised except for the LED I wish to add

#### Alec_t

Joined Sep 17, 2013
11,984
But the subject was full battery LED indicator, not technical types of batteries!
You can't design a 'full battery' indicator without knowing the type of battery. Different battery chemistries have different charge termination voltages.