2.0 Charge Controllers 2.1 Maximum Power Point Tracking: What is it? Have you ever wondered why you are not getting 60 watts of power into you battery when you paid for 60 watts of solar panel. A typical 60 watt panel produces 3.5 amps into your 12 V battery. This is 12 X 3.5 = 42 watts, not the 60 that you paid for -- why? The key hides in the voltage that the panel produces its full power. For a typical 12 volt panel, the panel produces its full power at about 17 V - read the label on your panel, but your battery is forcing the panel to 12 V - creating a mismatch that is affecting how much power you are getting from the panel. Wouldn't it be great if the panel produced its power at 17 volts, and all the power went into your battery at 12 V. This is basically what our charge controllers do and this is where the extra charge current we speak of comes from. Solar Converters Charge controllers perform 2 functions simultaneously, they track the maximum power point of the panel to get the most power from your panel investment, then use an ultra high efficiency DC-DC PWM converter to "transform" this maximum power point power to the battery voltage, giving an effective increase in charge current over normal charge methods. The increase in current is simply the same percentage difference between the panel Maximum power point and the battery voltage (less efficiency). The bigger the difference, the more charge current is delivered. This means the more discharged the battery is the more current the MPPT will put into it. The nemesis of this scheme is very hot panels, where the Maximum Power point voltage is the same as the battery voltage i.e. no increase at this time, however as the sun angle moves and the panels cool, the increase will come back. The maximum power point tracker part adjust the operating parameters continuously "on the fly" of the DC-DC converter to keep the power transfer at its maximum. There simply is no more power available. This has significant advantages on cold panels, where we have seen 40% more battery current. On hot panels, the panel characteristics move the maximum power point voltage down close A nice feature of the DC -DC converter is it is a true DC-DC conversion, with DC voltages in and out. It even produces smooth Dc voltage at the float voltage without the battery attached (say battery fuse blew) so your equipment will not be overvoltaged. Figure 2.1 shows a typical system setup. It is connected much the same as any other systems. Our charge controller have integral fusing and LVD so you just hook up the panel, a battery and load and your done. 2.3 The Newer High Voltage Panels A trend seems to be towards higher voltage panels, for example BP Solar's excellent 90 watt panel. This panel has a very high maximum power point voltage relative to 12 V batteries. This gives a high percentage difference between the MPP voltage and the battery voltage, giving rise to great increases in charge current for your battery above what you would expect from a higher panel, even when hot. 2.4 Voltage Conversion: Charge Low Voltage Batteries from High Voltage Panels Some applications may require the panels to be a long way from the battery to be charged. For example home owners may not like the "look" of the panels and want them to be far away out of sight. In order to carry power over a few hundred feet, a very heavy gauge of wire is required., hence cost. The answer of course is to carry the power at high voltage over the distance, then transform it down to the battery voltage at the battery. This gives great saving in wiring, not to mention the aggravation of handling heavy wire over long distances. Solar Converters charge controller have an integral DC-DC converter in them. As a voltage conversion is done anyway, this voltage conversion can be between 2 entirely different voltage classes. For example, 65 V MPP panel charging a 24 V battery with MPPT tracking on the panel and transforming all the power to your 24 V battery. As it is impossible to stock all combinations of input voltages and output voltages, these units are custom units, usually with only the change of a few resistors to "tell" the unit what the voltages are. Please call the factory with your needs. 2.3.2 Using "odd" voltage panels Some panel manufactures produce "odd" panel voltages that are cost effective on a power basis or have some other neat attribute, but are at the wrong voltage for your system. An example are some of the newer panels produced in quantity for direct to utility conversion, not really for 12 V systems. The panels may now be used to power your system. Please contact the factory with your needs for input and output voltage. 2.3.2 1.5 V NI-CAD charger Some applications, like railway switching require very low voltage batteries. Model PT 12/1.5-10 will float charge control a 1.5 V NI-CAD battery from a 12 V solar panel. In this case, the percentage difference between the panel MPP and the battery voltage is very great, giving tremendous current into the NI-CAD. Even a single 20 Watt 12 V panel puts over 10 amps into the NI-cad. Other charge voltages available. Contact the factory with your needs. 2.4 Timed Load Functions Some functions, like security lighting, billboards, pond aeration, walkway lights, backup lighting, or any other function where you may like to disconnect the load without a large disconnect. All Solar Converters Charge controllers have a small signal input that opens the LVD relay, effectively disconnecting the load from the battery. This may be driven by float switches, event timers, a solar panel, or any other switch device that will actuate to turn your load off the battery. 2.5 High Voltage Charge Controllers High Voltage normal charge controllers are few and far between, mainly due to the problems of switching high current DC loads on and off at high DC voltage and the power used to drive these relays that have the required ratings. See Figure 2.5 As the basis of our charge controller is a DC - DC converter, operation at high voltages poses no unusual constraints. For very high voltage systems, our charge controllers can be married to our auxiliary supply to supply auxiliary rails. Solar Converters Inc. design expertise, includes a number of 150,000 V X-ray generators done with DC-DC converters, making charge controllers under 10 KV well within our reach and quite possible with components readily available. Please contact the factory with your high voltage charge controller needs.Last Updated -- October 1998