PWM solar charger

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raymond86

Joined Jun 19, 2010
2
i need help in designing pwm solar lead acid battery charger. I have designed the charger circuit and when i simulated it, it worked and when i constructed it, it failed to charge the 12V battery.the pwm signal will be geberated by a PIC 16F877A microcontroller. I have uploaded the circuit please help me rectify the problem.
 

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russpatterson

Joined Feb 1, 2010
353
Interesting design. Are you using a standard solar panel that outputs 18-22V? What's L1, the inductor, for? Are you doing a buck converter? I don't think you need to do that unless you want to add the MPPT type stuff to your circuit.

I have a schematic, work in progress, on my blog you can check out that does a battery charger and a motor controller. No MPPT yet for just battery charging but effectively works that way when running the motor.

http://backyardsolar.blogspot.com/
 

SgtWookie

Joined Jul 17, 2007
22,230
I don't know why you are using an LM350 regulator, as that is throwing away a good bit of power by generating heat.

Like hgmjr says, your caps are upside-down.

The MOSFET is installed backwards. The body diode will conduct continuously, and the MOSFET will get hot.

The method of discharging the gate will result in slow turn-off times and a hot MOSFET.

D1 is inadequate for the current, and it is not a fast recovery type.

C1 is far too small.

The PIC16F877 is obsolete. You will pay considerably more for that uC than it's more modern replacement, the PIC16F887.
 

retched

Joined Dec 5, 2009
5,208
I agree with the sarge.

A re-design is in you best interests.

I would start with the PIC. Get yourself a nice cheap and powerful 16F887 then go from there.
 

SgtWookie

Joined Jul 17, 2007
22,230
Have a look at the attached article; a MPPT charge controller that doesn't require a multiplier.

You might consider implementing the math in the uC. Remember though, using math operators in C (or other language) on a PIC will bloat your code really quickly.
 

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retched

Joined Dec 5, 2009
5,208
I may be lost in the mix, help me out.

You are trying to charge a battery (lead acid 12v type) using a solar panel or array.

You are bucking the voltage?

What is the output of the solar system?

The way I am envisioning it, the PIC could be measuring the voltage of the battery between pwm high pulses to get the battery charge level.

The PWM signal sent from the pic triggers a mosfet that lets the solar power get to the battery.

As long as the charge time for the caps are faster than the PWM level, and the voltage of the cap output doesn't exceed the mosfet ratings, all should be good.

Now, The voltage from the panel(s) should be set to the fast charge, then trickle charge levels. You could use resistors and or linear regulators for this process, but the whole point, to me, is to NOT waste the power from the solar panels.

If theres heat there is waste.

Are you using the battery while charging it?
 

retched

Joined Dec 5, 2009
5,208
Doing some research, you may want to think of using this:
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1078,C1089,P89360

This is a very impressive IC. It handles the charging, safety, and all that good stuff.

From the description from the linear website:
The LT3652 is a complete monolithic step-down battery charger that operates over a 4.95V to 32V input voltage range. The LT3652 provides a constant-current/ constant-voltage charge characteristic, with maximum charge current externally programmable up to 2A. The charger employs a 3.3V float voltage feedback reference, so any desired battery float voltage up to 14.4V can be programmed with a resistor divider.

The LT3652 employs an input voltage regulation loop, which reduces charge current if the input voltage falls below a programmed level, set with a resistor divider. When the LT3652 is powered by a solar panel, the input regulation loop is used to maintain the panel at peak output power.

The LT3652 can be configured to terminate charging when charge current falls below 1/10 of the programmed maximum (C/10). Once charging is terminated, the LT3652 enters a low-current (85μA) standby mode. An auto-recharge feature starts a new charging cycle if the battery voltage falls 2.5% below the programmed fl oat voltage. The LT3652 also contains a programmable safety timer, used to terminate charging after a desired time is reached. This allows top-off charging at currents less than C/10.
 
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