9V rechargeable battery circuit

Hi, One of my friend shared this circuit which charge 9V rechargeable battery with all protections(Overcurrent, Overvoltage, EMC, etc).

Is this circuit has any disadvantages. Kindly explain.

hemnath said:

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my friend shared this circuit which charge 9V rechargeable battery with all protections(Overcurrent, Overvoltage, EMC, etc).

Is this circuit has any disadvantages.

Click to expand...

Whatever protection you have, the term galvanic isolation is not associated with this charger. You should use galvanic isolation for mains powered system.

This charger poses a serious electric shock hazard to both technicians and users. Contact with mains can drive high currents through the body.

Input will be galvanic isolation. 230V AC to 12V AC.

The 12V AC is the input to this circuit.

charge 9V rechargeable battery with all protections(Overcurrent, Overvoltage, EMC, etc)

Click to expand...

The description doesn't match the circuit. The only clear protection is against reversed battery connection (Q1, R2, D6). I don't recognize current limiting or effective voltage limiting. You also didn't mention the battery type.

Under circumstances, the output impedance of the transformer might be utilized as poor man's current limiter. But the zener diode hardly provides useful charging voltage limiting.

By the way, what's the unnamed black square meant to be?

Battery type: 9V Lithium Ion rechargeable battery.
Black square will be Fuse I think so. I'll ask my friend and confirm you soon.

Hi,

Li Ion batteries need very tightly tolerated cut off voltage. Read the battery datasheet and follow the charging recommendations. Overcharging a Li Ion battery may lead to explosion and fire. It's no fun, so take care.

Klaus

The schematic was missing the AC input voltage, the battery type (Lithium-Ion), how many cells the battery has (so we know its maximum charging voltage) and now it is missing the mAh rating so we know how much current limiting the circuit should have.
The circuit is poorly designed and will not charge the battery but luckily it also will not explode the battery:

1) The 1N4744 15V Zener diode will do nothing most of the time but it might blow the fuse if the input voltage becomes higher than 12VAC.
2) The high voltage IRF720 Mosfet will also do nothing since it has nothing to turn it on. It will turn on if its gate voltage is somewhere around +20V but with no current limiting.
3) The 1N4742 12V Zener diode will also do nothing.

Your friend who designed this circuit should learn about how to safely charge a Lithium-Ion battery from www.batteryuniversity.com then learn the basics of electronics.

In addition to a wide initial tolerance, common zeners have a significant tempco and a very soft knee.
In other words, *very sloppy* charging characteristics.

As Klaus mentions, Li ion batteries are sensitive about its charging requirements. In the best of cases, you'll have a not-completely-charged battery. In the worst case, you'll end up with a ruined battery, and in many cases the failure could prove to be catastrophic.

EDIT: After re-reading your original post, I noticed that this is a N-chan Mosfet! As Audioguru mentions, it will never turn on.

I suggest you accept no further circuits from this "friend" as he obviously does not know what he is doing.

Hi all,

I have asked another friend to design a battery charging circuit with sufficient protection.

Kindly check and provide your comments.

Battery: 2 lithium 3.6V => 7.2V battery, 1050-1150mAh

It would take me all week to unscramble that schematic but based on all the connections to the battery and 'device' leaving the emitter of a 2N2222, my first impression is it will not work, at least any better than a simple current limiting resistor!

Brian.