9Volt Battery charge Indicator (LED)

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Greetings to all ,

Today i successfully Developed a (TDA2822 based) Mini Stereo system for my Mp3/Mobile , i have attached some pics if interested in taking a look at it .

It has a very lovely output (crystal clear stereo sound) & no distortion at all, Thnx to
"Bertus" as he helped me a little to figure out the RFI problem i was facing.

The feature i have added in this system is that it is equipped with USB charging system , that charges the 9V 200mAh rechargeable battery fitted inside.

Presently everything is fine with the stereo system , all i need to do next is make a simple LED charge indicator , when the battery is fully charged , the LED should Lit & i can disconnect the USB supply.

So, Any help will be deeply appreciated .

Best regards,
Lubnaan


 

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MikeML

Joined Oct 2, 2009
5,444
Here are two voltage detectors, one which lights a LED on voltage rise, and the other on voltage drop. You can easily tailor them to different voltages...

Be advised that during charging, the fact that a battery reaches a particular voltage is NOT a reliable indicator that the battery is fully charged. The correct way to do it is to charge using a current-limited, constant-voltage power supply, watch the current flowing into the battery, and terminate charging when the current drops BELOW a threshold.
 

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Last edited:

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Here are two voltage detectors, one which lights a LED on voltage rise, and the other on voltage drop. You can easily tailor them to different voltages...

Be advised that during charging, the fact that a battery reaches a particular voltage is NOT a reliable indicator that the battery is fully charged. The correct way to do it is to charge using a current-limited, constant-voltage power supply, watch the current flowing into the battery, and terminate charging when the current drops BELOW a threshold.
Thank you MIKE , noted your points , & will try to experiment wth the same .

Best regards
Lubnaan
 

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
This 12 Volt Battery Auto Charger circuit will quickly and easily charge most any lead acid battery. When the battery is fully charged, the circuit Relay switches off and lights a LED.

I would like to know , can this circuit be used in 5 volt application ,
Will this be able to charge 9V NiMH battery & whats the use of a 10K pot here ???

REGARDS
 

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MikeML

Joined Oct 2, 2009
5,444
The circuit you posted is marginally (it is a poor design) suitable for charging Lead-Acid batteries. It is not suitable at all for NIMH batteries, which require a different charging algorithm.
 

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Hello,

Is it possible to make a cutoff circuit using a resistor (heat sensor) which can shut down the charger if the battery's temperature reaches 33 degree in case of overcharging/overheating .

Regards
 

Audioguru

Joined Dec 20, 2007
11,249
Why not use a battery charger IC that is designed to charge your battery properly?
It has a temperature sensor as a backup in case it fails to sense that the battery is fully charged. The IC will refuse to over-charge a battery that is already charged.
 

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Why not use a battery charger IC that is designed to charge your battery properly?
It has a temperature sensor as a backup in case it fails to sense that the battery is fully charged. The IC will refuse to over-charge a battery that is already charged.
Can you plz be specific about the IC , i mean any recommendation which is easy to find .
 

Audioguru

Joined Dec 20, 2007
11,249
I have never been to the Ukraine so I don't know if Maxim battery charger ICs are available there. I think most American and European semiconductor manufacturers make battery charger ICs.
 

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
No , Maxim ICs aren't available in Ukraine.

Here's one LED indicator i found , looks quiet simple .
The red led will blink when the battery charge is less then 6.9 V & the green Led will blink when the charge is more then 6.9 v.

Is it possible to make some modifications in the circuit in such a way that the Green light should blink when the charge is more then 8.3 volts ?
 

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Audioguru

Joined Dec 20, 2007
11,249
A "9V" Ni-MH battery is either 7.2V or 8.4V. It is either 9.8V to 10.5V or it is 11.2V to 12V when it is fully charged.

it will not be charged much if it measures only 8.3V when it is charging.

A battery charger IC detects the very small voltage drop that occurs when a Ni-MH battery becomes fully charged. Your simple LED cannot do this.

Look at the Ni-MH Battery Applications Manual online at Energizer. It shows a graph of the typical voltage of a charging Ni-MH cell. The voltage is higher when the charging current is higher and changes with temperature changes. Each battery is a little different. If you over-charge a Ni-MH battery then its life is shortened.
 

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Thread Starter

lubnaan90

Joined Jan 13, 2010
198
A "9V" Ni-MH battery is either 7.2V or 8.4V. It is either 9.8V to 10.5V or it is 11.2V to 12V when it is fully charged.

it will not be charged much if it measures only 8.3V when it is charging.

A battery charger IC detects the very small voltage drop that occurs when a Ni-MH battery becomes fully charged. Your simple LED cannot do this.

Look at the Ni-MH Battery Applications Manual online at Energizer. It shows a graph of the typical voltage of a charging Ni-MH cell. The voltage is higher when the charging current is higher and changes with temperature changes. Each battery is a little different. If you over-charge a Ni-MH battery then its life is shortened.
NOTED ! Thank you
 
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