constant voltage, constant current Lead Acid Battery Charger

[Erwin_Macaraig]

I am doing a Lead-Acid, constant voltage, constant current Battery Charger using PWM.
I use AT89C51 Atmel microcontroller to generate the charging current through the battery
and a N-channel MOSFET transistor.
The intended operation of my circuit is as follows
1. The circuit will first charge the battery at a minimum level.
2. The circuit will monitor the battery voltage through the Battery Voltage Monitor Section of
the circuit (I use a 13V zener diode to trigger the transistor
that will give the microntroller the signal that the battery has reached
13V). As long as the battery voltage does not exceed 13V. The microcontroller
will increment its charging current little by little.
3. The circuit will then monitor the charging current as it is incremented, through the Current Sensing
Section (across R1 - 0.22 ohms 5W resistor). If the current reaches three amperes,
theoretically the voltage across the R1 will be .66V and then I will amplify it
in a voltage level that could trigger the Zener diode D5. Thus feeding this signal
to the microcontroller through transistor T3. The circuit will then maintain the
three-ampere charging current.
4. Reaching the three ampere charging current, the circuit will now monitor again the battery
voltage through the Float Voltage Monitor section of the circuit. If it reaches
14V, then the circuit will switch to trickle charge sso that the battery will not
be overcharge.

Any comments and suggestion will be much appreciated. I tried building a prototype,
I observed that the IRF emits excessive heat in spite of having
a heatsink. I also monitored the pulse width
modulation of the AT89C2051 through an oscilloscope and the results is not consistent.
Sometimes the processor hangs. Is it due to noise and crosstalk?
Thanks in advance!!!

 

[chrisking]

is there anyway to modify you circuit to work with two batteries and depending on the state of charge of the batteries. It will automatically sense the state of the batteries and switch the load from the lowest charged battery to the highest charged battery then proceed to charge the discharged battery.