lead acid battery charger using PWM

[abdoalghareeb]

I want to build battery charger using AVR and PWM.
Is it possible ?
This is my simple schematic.

 

[Tahmid]

With the potentiometer turned up all the way to the "top side" in your schematic, the voltage to the ADC input will be more than 5V. For safety of the microcontroller, you should thus redesign your voltage divider network to limit max voltage to less than 5V. Consider adding a 5.1V (or 4.7V) zener across the ADC input to prevent damage.

You should use a low-side MOSFET driver instead of driving the IRF3205 directly from the microcontroller. The way you have it now, you won't be fully turning the MOSFET on. You should have at least 8V VGS to ensure that you have fully turned on the MOSFET.

You can't measure the battery voltage if the battery isn't being charged since your battery -ve is not connected to ground. Consider using a P-channel MOSFET in the high-side configuration to ensure that your battery -ve is common grounded (to the circuit).

The +12V rail is incorrectly labelled since the voltage won't be +12V.

I assume that you're trying to charge a lead-acid battery. Am I correct?

Hope this helps.
Tahmid.

 

[abdoalghareeb]

thanksssssssss
All your notes are helpful 100%.
another questions :
-In general, is the Principle of my design the best method of charge battery using MC and PWM ?

-I can't find in the local shops P-channel MOSFE as high as N-channel MOSFE current. also I will supply the circuit from the battery if the main 220 VAC turned off. is there another way?

 

[Tahmid]

You can make a very simple boost circuit to boost up the voltage so that you can drive the N-channel MOSFET in the high side configuration. In fact, you can even generate the required PWM signal from the ATmega itself. You can't use a capacitor-based bootstrap driver if you have high duty cycles.

Your method looks like it's going to employ a form of 'pulse charging' to 'regulate current' (which if you want to do you need to measure the current using a shunt for example). If you plan on just turning the MOSFET on and leaving it on until the battery is charged completely, that's not a great idea. You'll have no control of the current and can easily damage the battery.

One method employed in many commercial inverters is to control the charging on the primary high voltage side of the transformer using a triac and a lower voltage tapping on the primary. By using phase angle control, the voltage and current on the primary side and thus the secondary are controlled. While this isn't necessarily the best method, it's one that's widely used and works well.

Hope this helps.
Tahmid.

 

[panesar]

abdoalghareeb
battery rating is 100ah in ur schematic
so for best results charging current upper limit should be 10amps

try to make a current loop in the MC to vary the duty cycle
for that u also need a current sense resistor

 

[Tahmid]

abdoalghareeb
battery rating is 100ah in ur schematic
so for best results charging current upper limit should be 10amps

try to make a current loop in the MC to vary the duty cycle
for that u also need a current sense resistor

For a 100AH battery, charging current should be more than 10A when the battery isn't near fully charged. If you use 10A current all the time, the charging time will be too long (> 10 hours from fully discharged to fully charged). Usually you can charge at a higher current if you're careful enough to reduce current before overcharging.

 

[abdoalghareeb]

You ask me to use a shunt or resistor as current sensor .
I read this document (curve page 2)and I notice that I can monitor a Battery State of Charge depending on its voltage .So I think I don't need to current sensor .
What do you think ?

https://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

 

[panesar]

The curves are temperature dependent
If 200Ah battery has discharge of 50A and a 100Ah has discharge of 25A , both will show same curve char. (i think so)

Ur MOSFETs can handle only limited current (say around 10Amps)
Or use bank of MOSFETs for large currents

The current sense will only save the MOSFET from burning down in charging and discharging
Protections like overcharging and overload can be achieved

PANESAR