Float Charger

[AliasZ50]

I found this circuit on a page and i want to do it, but i don't understand what's the point of the capacitor in the circuit and i'm kinda new to electronic circuits , could someone explain it to me ?

 

[Externet]

The manufacturer of the voltage/current regulator IC recommends the use of a capacitor in its data sheet for better behavior under input spikes or ripple.

 

[AliasZ50]

The manufacturer of the voltage/current regulator IC recommends the use of a capacitor in its data sheet for better behavior under input spikes or ripple.

Thanks a lot!! but what about the transistor connected to the regulator ?

 

[Bluejets]

Seems you are unappreciative of #2 with your exclamation marks.
You didn't ask originally about the transistor, just the capacitor.
However, the transistor monitors current (RCL) and adjusts the regulator output to suit, depending on set point.( I would imagine)

 

[Audioguru]

When the charging current causes a voltage of more than about 0.7V across the 1.2 ohm resistor (0.7V/1.2 ohm= 583mA) then the transistor turns on and drops the regulator voltage which limits the current.

The horrible circuit does not detect that a battery is fully charged then it over-charges the battery that is bad. Ni-MH battery manufacturers recommend disconnecting the charger when the battery is detected to be fully charged.

 

[AliasZ50]

Seems you are unappreciative of #2 with your exclamation marks.
You didn't ask originally about the transistor, just the capacitor.
However, the transistor monitors current (RCL) and adjusts the regulator output to suit, depending on set point.( I would imagine)

Sorry that wasnt my intention , english is not my native lenguage so expressing myself can be hard

 

[AliasZ50]

Thanks for the info , but i have one last question: Why is there a diode attached to the regulator ?

 

[(*steve*)]

There are 4 diodes.

The green LED lights if there is input power, or if sufficiently charged batteries are present.

The red LED lights when input power is connected, sufficiently charged batteries are connected, but not if the batteries are shorted.

The diode D1 protects the circuit from power being connected backwards.

The diode D2 protects the base emitter junction of the main pass transistor in the regulator which can be damaged if more than 7 or 8 voltage of batteries are connected to the charger without input power and with C1 discharged.

As you can see, the LEDs don't really indicate anything special.

It's also really odd that it has two forms of current limiting.

then it over-charges the battery

It may not. It might under charge them instead.

 

[AliasZ50]

There are 4 diodes.

The green LED lights if there is input power, or if sufficiently charged batteries are present.

The red LED lights when input power is connected, sufficiently charged batteries are connected, but not if the batteries are shorted.

The diode D1 protects the circuit from power being connected backwards.

The diode D2 protects the base emitter junction of the main pass transistor in the regulator which can be damaged if more than 7 or 8 voltage of batteries are connected to the charger without input power and with C1 discharged.

As you can see, the LEDs don't really indicate anything special.

It's also really odd that it has two forms of current limiting.



It may not. It might under charge them instead.

Thanks i really appreciate the help

 

[AliasZ50]

I don't want to be annoying , but i want to know if the batteries should be in connected series or parallel

 

[(*steve*)]

Connect them as shown in the schematic. In series.

 

[AliasZ50]

Connect them as shown in the schematic. In series.

thanks i'm really new with this

 

[AliasZ50]

When the charging current causes a voltage of more than about 0.7V across the 1.2 ohm resistor (0.7V/1.2 ohm= 583mA) then the transistor turns on and drops the regulator voltage which limits the current.

The horrible circuit does not detect that a battery is fully charged then it over-charges the battery that is bad. Ni-MH battery manufacturers recommend disconnecting the charger when the battery is detected to be fully charged.

What can i add so it detects when the battery is fully charged?

 

[(*steve*)]

What can i add so it detects when the battery is fully charged?

For NiMH, the easiest method would be either a dedicated chipset or a microcontroller and lots of programming.

Detecting SOC for these batteries is non-trivial.