Hi guys,
I am designing a circuit of battery charger of lead acid battery using PWM microcontroller which will help in getting effective voltage and current using shunt resistor. ADC pins of Arduino micro will be used across the resistor to calculate the current(resistor value is known).
By reading some forums came to know that MOSFET should be used but don't know how to use and which should be used.
Any help will be much appreciated.
Thanks
charlie_chap:
across the resistor to calculate the current(resistor value is known)
But please don't show us the schematic as that would help us to help you.
Your description has me worried. We need a circuit to work out what you are doing.
Weedpharma
I think maybe from your post your target is to get maximum charge into the battery in minimum time. The first step in this is to define the strategy or algorithm you intend to use.
I have a very good commercial battery charger (lots of $) which I've dug into. Starting with a dead battery it charges at constant current and the voltage rises until the battery reaches a preset high voltage then it switches to constant voltage and the current falls until it drops to a preset low current then it switches to a low constant "trickle charge" current which it holds forever.
All this is software development inside the Arduino.
The biggest task ahead of you is to develop the power supply. You need 20 amps or so at 16 or 18 volts (maybe 20) available so a transformer to go from your domestic supply (120 or 240 vac 50 or 60 Hz depending on where you are) to the low voltage then a rectifier to get DC then a control element, transistor or MOSFET, possibly several in parallel to get the current needed.
The voltage and current feedbacks to the Arduino will come from a voltage divider bridge and a series resistor respectively. One little "gotcha" is that to decide when to switch from current control to voltage control you must turn off the charging current and measure the open circuit voltage then make the decision. My charger does this every few minutes.
If you're going to develop this project start by writing out what your strategy is, then make a block diagram showing each function in its own block and how they are connected to implement the strategy then start designing and testing each block, both hardware and software and only then can you put it together into a working system.
It's probably a bigger job than you originally contemplated.