Post #9606

Solar Battery Chargers. These come in two varieties. PWM are the older ones and MPPT are the newer ones. 1)PWM. In short, don't use these. They are not efficient. If these were a car, you would have a one speed transmission and would have to slip the clutch to make the car move. Because of the way they work, solar panels end up not operating in their ideal voltage range. Back about 15 years ago they are all that was available. Most commonly seen in 12v systems like the Harbor Freight solar kits. 2)MPPT. If MPPT chargers were cars, these would be the CVT (constant variable transmission) version. These have a computer on board that finds the sweet spot in the solar panel's power output and keeps it running at that level. It converts that power down to the voltage of your battery. An example is you have 4 solar panels making 2000watts at a specific voltage and amps. if you reduce the load on them, they "rev" too high and get out of their power band. if you load them down too much they drop to a lower "RPM" and make less power. The MPPT's job is to figure out what "speed" these panels make the most power at and convert that down to the battery voltage. Let's imagine that the panels are making 10amps at 200vdc but the battery is at 50v. In my car analogy, we need a 4:1 ratio transmission.... and so the MPPT ends up converting 200v down to 50v and the amps goes from 10amp from the solar panels to 40 amps into the batteries. 200v x 10amp = 2000w.... and 50v x 40amp = 2000w. It does this with a 99% efficiency.