Things that Work! Home Power tests the Heliotrope CC-20 PV Charge Controller A photovoltaic charge controller keeps the PV array from overcharging the battery. Sounds simple enough, but over the years many, many electronic solutions have been designed for controlling the PVs output. Some worked, and some didn't. Some lasted and some failed within hours of installation. This one works and lasts. The Heliotrope CC-20 is a series type PV controller that will handle arrays of up to 20 Amperes and in either 12 or 24 VDC systems. The CC-20 uses a very effective method of controlling the array while also maintaining the highest possible state of charge in the battery. How the C-20 PV Controller Works There are two basic types of PV controllers: series and shunt. They both perform the same function: voltage regulation of the system to prevent overcharging the batteries. A series controller essentially disconnects the PVs from the battery when they are full. A shunt regulator adds an electrical load to the system and the additional consumption of the shunt load keeps the system's voltage within limits. The CC-20 is a series type regulator. It pulse width modulates (PWMs) a metallic oxide semiconductor (MOS), field effect transistor (FET) ON and OFF in response to the battery's voltage. If the battery isn't full, then the CC-20 passes all the PV array's power to the battery. When the battery gets full, the CC-20 rapidly turns the MOS FET on and off (many times per second) to maintain the battery at the fullest state of charge possible. Relay type controllers, however, totally disconnect the array from the battery. This is not only less effective in maintaining the battery, but also wastes already paid-for, pollution-free solar energy. The PWM scheme that Heliotrope uses in their controllers pulses the array to maintain a constant system voltage. Net result is a fuller, better maintained battery and less wasted energy from the PV array. The use of a MOS FET instead of a relay enormously increases the reliability of the controller. Relays are very failure prone since they use moving parts and mechanical electrical contacts. Transistors on the other hand have no moving parts and all the connections are soldered. Installing the CC-20 The unit arrived in good shape and was ruggedly packaged. The documentation was adequate to program and install the CC-20. We put this test CC-20 in series between a PV array of 4 Kyocera J48 modules (producing Å12 Amperes at 12 VDC) and a set of 4 Trojan L-16W batteries (storing Å700 Ampere-hours at 12 VDC). The CC-20 is user programmable for system voltage (we choose 12VDC) and state of charge voltage regulation point. We choose 15.0 VDC as the PWM voltage level of the controller. This voltage level is user adjusted on a set of small switches. You can set the unit as low as 13.2 VDC (26.4 for 24 VDC systems) and as high as 15.0 VDC (30.0 for 24 VDC systems). CC-20 Performance We've had this regulator in line now for about four months and it works great. Some of the features we like are it's built-in LED bargraph metering for both system voltage and PV array current output. These two bargraphs can be read from across the room and tell all you need to know to run the system. The ammeter was somewhat generous and read high. Heliotrope has informed us that the metering circuit has been fixed and is now accurate. The system voltmeter was checked against a Fluke 77 DMM and proved accurate. The controller also has several other features. There are three status LED lights on its front. One lights when the PV array is producing electricity. Another indicates that the batteries are fully charged and that the controller is regulating (a good time to vacuum the floors). The third indicator informs the user if the regulator has shut itself off because of overtemperature. Rather than french fry its MOS FET into destruction, the CC-20 will shut off the FET if its temperature gets too high. The CC-20 is also protected against reverse polarity hook-up. There is a front panel switch that selects one of two battery packs (great for RVs). CC-20 Cost and Conclusions The CC-20 costs around $180., complete with LED bar graph metering. This controller offers excellent value for its cost. It is effective, easy to install, user programmable, virtually indestructible, and best of all it treats the batteries right. We highly recommend it to any PV system user with an array of 20 Amps or less. For bigger systems, Heliotrope uses the same PWM scheme in controllers up to a whopping 120 Amperes and that at either 12 or 24 VDC. The Heliotrope PWM Controllers work better than any other PV regulation device we've ever used (and there have been more than a few that were "Things that DON'T Work!"). RP