....@mikeMI,
...When the voltage of the battery is below 14 V, the PWM is at maximum duty cycle which charges the battery at Vmp of the panel. When the battery voltage rises upto 14 V, the duty cycle is reduced so as to keep the battery at trickle charge....
A simple on/off switch wont perform this.
Using MPPT tracking for charging lead-acid batteries is a total waste of time.
If you simply connect a ~20Voc solar panel to a 14V LA battery, the panel is so close to its MP voltage, that the switching losses in a MPPT tracker totally cancel out the few percent gain that you could potentially achieve by operating the panel at a volt or two higher (nearer its actual MP voltage...
Charging a battery implies that at some point in the solar cycle, the battery achieves full charge, and the available panel power after that point is lost anyway..., so why worry about saving a couple of % during the actual charging time? The whole MPPT thing only makes sense if you are generating AC power and putting it back on the grid (i.e., you have a load which absorbs all of the available power, which a battery does not).
I just use a simple on-off switch (PFET) to connect-disconnect the panel from the battery. A simple Schmitt-trigger voltage sensor controls the gate of the PFET. Algorithm is for a SLA is dirt simple: Connect the panel to the battery when the battery voltage drops below 13.2V; disconnect the panel from the battery when the voltage reaches 14.7V.
In my case, there is an intermittent load (green house thermostatically-controlled vent open/close actuator, water misting pump) that occasionally draws down the battery voltage, and starts a new charge cycle. If none of the loads turn on, and the battery just sits full, it takes several hours for its terminal voltage to drift down below the cut-in voltage, at which point the panel is reconnected to the battery until it reaches the cut-out voltage. That would happen about once per solar day, and it only take a couple of minutes, assuming none of the loads come on. If they do, they trigger a recharge cycle that takes longer...