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battery charger circuit

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Advanced Member level 2
Mar 21, 2015
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Hi all....
i have made a small project which works on 7.4v li-ion battery. my issue is can i charger my battery with normal 9v power adaptors or do i need a battery charger adaptors. will my 9v power adaptors charge the battery full. is 9v compatible or should i use 12v charger or power adaptors.
my battery has a inbuilt over charge protection circuit.

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my battery is 7.4v 2200mah and am using 9v 1mah to charge

A Lithium battery is EXTREMELY DANGEROUS if it is charged wrong. It can explode shooting bits of burning melted Lithium metal all over and/or catch on fire and the fire is extremely hot and water on it makes it burn hotter. Go to www.batteryuniversity to read about the maximum voltage it can be charged to (8.40V) and its maximum charging current (its label or manufacturer will tell you) and it must have the charger disconnected by a circuit that detects a full charge (low current, not 8.40V voltage).

The charge protection circuit in your battery is not a charger circuit. It probably disconnects the charger if it detects the voltage or current are wrong.

A Lithium charger circuit also measures the voltage of the battery at the beginning of charging. If it is less than about 6.4V for your battery then it will refuse to charge or it will try charging at a low current. If the low current does not cause the battery voltage to rise then it shuts off the charging because charging a low voltage Lithium battery can cause it to catch on fire.

What is 1mAh? It is a very small current of 1mA for a duration of one hour which will not charge your battery.

sorry.... its 9v 1000mah.
i agree with you.... but my question is can i charge the battery with normal power adaptors or i need to charge with the charging adaptors only....
are charging adaptors different from power adaptors...
i have placed a over charge protection circuit. which cuts off at 8.2V.

What is a "charging adapter"? Is it the power supply for the charging circuit that is inside a cell phone? It is called a charger but it is not a charger, it is just a power supply.
You need a charging circuit that probably uses a Lithium battery charger IC. The charging circuit can be powered from an normal power adapter.

You do not want the charging to cut off when the battery reaches 8.2V because then it is only about half of a full charge. The Battery University explains that a Lithium battery is fully charged when its charging current is detected to drop to 1/40th its rated current, then the charging circuit turns off the charging.

gauravkothari23, I just want to back up what Audioguru is saying.

I have used a lot of Li-ion cells, often without protection circuits, and they stll make me nervous after years of using them.

Mis-charging a NiCd or NiMH, or even a lead-acid, is not very hazardous. Most likely you will just reduce the cell's life. Mis-charging, over-charging or over-discharging a Li-ion cell really is dangerous, and the cell can even explode long after you have charged it as the damage continues internally. This has happened to people, it's not just theory. The cells can go off like fireworks when abused!

You must use a charger designed for your battery, or a specialised Li-ion charger that can be adjusted to the exact voltage and capacity like Radio Control enthusiasts often use for charging their battery packs. You cannot/must not use a basic power supply, NiCd/NiMH charger, or anything else not specifically intended to charge your exact battery.

There are integrated circuits readily available to build your own charger. You can power the charger circut however you want.

The protection circuit in a commercial Li-ion cell is not intended to do your job of regulating the charge, or anything useful to you really. It's purely there to (hopefully) stop catastophic failure (explosion/fire) if the cell is mistreated. Even so, do not rely on it to do its job if you don't do yours.

Buy a proper charger, or study some dedicated ic charger circuits (search here to start) and make one, that's not rocket science as it's mostly done for you in the ic. But don't think you can simply improvise a charger like you can for a NiCd.
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I forgot to say that your lithium battery has two cells in series. A charger for it must be a "balanced charger" that charges each cell exactly the same amount, even when the cells are different (and they will be a little different). A balanced charger makes sure that the cell with a lower capacity is not over-charged which might cause it to explode.

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