Solar charge controller charging after after set point

Thread Starter


Joined Dec 27, 2010
Hi everyone, been reading here for a long time but never post before .
I'm trying to build this circuit for a 30W panel and a 34WH battery.
I choose this one because all other circuits around N channel mosfets create a lot of heat after the battery has been charged.
So I build this one on a breadboard an test it out.
I find that after the set point has been reached the op-amp goes high turning on Q2 and essentially grounding the gate of the mosfet therefore shutting it down, the problem is that if I set the charge voltage to say 13.6 the mosfet would remain conducting past 14+ volts, one thing I notice is that the voltage at the gate never really gets to 0 volts but remains around 0.1 volts.
I'm using IRF9530 part for the mosfet which should be more or less compatible.
I did make some modifications on the left side of the circuit, I'm using a LM317 to make the reference voltage and 2x47k voltage divider for the battery voltage sensing this changes should not make any difference in the circuit operation I think.
Any hints would be very much appreciated.