Calling on Solar Techies
I have been thinking of going solar for some time and decided to pull the plug. My wants are a 400 to 500 watt system. I have four 12 volt batteries with 340ah. I am not planning on changing b...
Forum Discussion
Well said Steve.
There are several misconceptions in this thread. As stated well designed MPPT does not switch to PWM in absorption and float. It switches to CV (constant voltage) mode. Consider the edge case for a second - a 100V string of panels feeding a 12V battery, for half of the absorption phase the charge current is > 50% of the bulk current, if it was in PWM mode the current would be limited to about 15% of the bulk charge current. Secondly in float charge the current is very low, so you typically don't get any extra power out of an MPPT, but it is still not acting as a PWM charger. Consider if you turn a load on - the charger will ramp up the current to carry the load while keeping the voltage at the float set point (until it maxes out the available power).
The other thing to consider is that solar panels are NOT constant voltage sources, they are closer to constant current sources. This is hard to conceptualize, but will help understand how MPPT harvests 'lost power'.
For the OP, this doesn't make a huge difference as his panels are in parallel and it is a small system, but it is important to provide accurate information.
There are several misconceptions in this thread. As stated well designed MPPT does not switch to PWM in absorption and float. It switches to CV (constant voltage) mode. Consider the edge case for a second - a 100V string of panels feeding a 12V battery, for half of the absorption phase the charge current is > 50% of the bulk current, if it was in PWM mode the current would be limited to about 15% of the bulk charge current. Secondly in float charge the current is very low, so you typically don't get any extra power out of an MPPT, but it is still not acting as a PWM charger. Consider if you turn a load on - the charger will ramp up the current to carry the load while keeping the voltage at the float set point (until it maxes out the available power).
The other thing to consider is that solar panels are NOT constant voltage sources, they are closer to constant current sources. This is hard to conceptualize, but will help understand how MPPT harvests 'lost power'.
For the OP, this doesn't make a huge difference as his panels are in parallel and it is a small system, but it is important to provide accurate information.
StirCrazy wrote:
I tdhink people need to learn more about MPPT chargers before they recomend against them..... yes they benifit more during bulk charging, no they do not switch to PWM mode, they are a three stage MPPT charger so basicly a DC_DC charger that converts DC to AC then back to DC at the most efficent combination ov voltage vs current. in the summer on a nice day they may only give you an aditional 10% but in the winter when it is cold that number can go up to 40% or when its raining or overcast it will be inbetween. also you could basicly run pannels in series lowering the current while raising the voltage which allows you to get away with a small cable and less loss than running in parallel. if you can aford it it is always worth getting a MPPT controler, if you cant then dont worry about it, but you can always upgrade later, would just mean reconfiguring your pannels to take advantage of a series setup.
Steve
