Solar Controllers--Don't be a Sucker! :(
Just got to say it again, how it is we are sitting here for five months off grid on solar with no problems at all (third season on solar like this), using the non-programmable, non-MPPT, solar control...
Forum Discussion
BFL13;
MPPT - Panel Isc can be exceeded by using excess Volts when panel volts exceed battery Volts.
Peak Amps depends on the difference between the charging Volts and the battery Volts.
Consider morning Volts as the daily lowest battery volts. This is when MPPT kicks in with the best increase in Amps.
As the days charging progresses, the difference decreases and so does the percent of current increase.
PWM - max current is the Isc of the panel all day.
A 12V panel is used with a 12V PWM if the battery bank is 12V.
A 24V panel is used with a 24V PWM if the battery bank is 24V.
A 48V panel is used with a 48V PWM if the battery bank is 48V.
Not flexible!
PWM discards excess volts. This is why the Salvo's KD-135 panel works so well; it is designed to be used with PWM because it has a very low Vmp and a high Imp resulting is less excess volts dropped. As you can see in his chart, when the panel gets too hot, there is not enough excess volts, and the graph flattens. His panel is optimized for PWM.
What if the 135W panel was 135 Vmp and 1 Imp and the battery is discharged to 12.0V and you use 14.4V for Vabs:
The PWM would charge at 1.1A(allowing an extra 10% for Isc).
The MPPT would attempt 135W by 135/12 = 11.25A. The MPPT would lead the battery Volts until Vabs where 135/14.4 = 9.375A. MPPT would beat the PWM all day. What % gain is that?
MPPT is not cheaper until you run out of roof real estate.
HTH;
John
MPPT - Panel Isc can be exceeded by using excess Volts when panel volts exceed battery Volts.
Peak Amps depends on the difference between the charging Volts and the battery Volts.
Consider morning Volts as the daily lowest battery volts. This is when MPPT kicks in with the best increase in Amps.
As the days charging progresses, the difference decreases and so does the percent of current increase.
PWM - max current is the Isc of the panel all day.
A 12V panel is used with a 12V PWM if the battery bank is 12V.
A 24V panel is used with a 24V PWM if the battery bank is 24V.
A 48V panel is used with a 48V PWM if the battery bank is 48V.
Not flexible!
PWM discards excess volts. This is why the Salvo's KD-135 panel works so well; it is designed to be used with PWM because it has a very low Vmp and a high Imp resulting is less excess volts dropped. As you can see in his chart, when the panel gets too hot, there is not enough excess volts, and the graph flattens. His panel is optimized for PWM.
What if the 135W panel was 135 Vmp and 1 Imp and the battery is discharged to 12.0V and you use 14.4V for Vabs:
The PWM would charge at 1.1A(allowing an extra 10% for Isc).
The MPPT would attempt 135W by 135/12 = 11.25A. The MPPT would lead the battery Volts until Vabs where 135/14.4 = 9.375A. MPPT would beat the PWM all day. What % gain is that?
MPPT is not cheaper until you run out of roof real estate.
HTH;
John
