| A Solar Charge Controller is an essential part of | | | | This is called "pulse width modulation. Both |
| nearly all power systems that charge batteries, | | | | methods work well when set properly for your |
| whether the power source is PV, wind, hydro, | | | | type of battery. A Solar Charge Controllers |
| fuel, or utility grid. Its purpose is to keep your | | | | holds the voltage more constant. If it has |
| batteries properly fed and safe for the long term. | | | | two-stage regulation, it will first hold the voltage |
| The fundamental functions of a controller are | | | | to a safe maximum for the battery to reach full |
| quite simple. Charge controllers chunk reverse | | | | charge. Then, it will drop the voltage lower, to |
| current and prevent battery swindle. Some | | | | sustain a "finish" or "trickle" charge. Two-stage |
| controllers also prevent battery overdischarge, | | | | regulating is important for a system that may |
| protect from electrical overload, and/or display | | | | experience many days or weeks of excess |
| battery status and the flow of power. Let's | | | | energy. It maintains a full charge but minimizes |
| examine each function individually. | | | | water loss and stress. The voltages at which the |
| Jamming overturn Current: | | | | controller changes the charge rate are called set |
| Solar Photo Voltaic Module work by pumping | | | | points. When determining the ideal set points, |
| current through your battery in one direction. At | | | | there is some compromise between charging |
| night, the panels may pass a bit of current in the | | | | quickly before the sun goes down, and mildly |
| reverse direction, causing a slight discharge from | | | | overcharging the battery. The determination of |
| the battery. The potential loss is slight, but it is | | | | set points depends on the anticipated patterns of |
| easy to prevent. Some types of wind and hydro | | | | usage, the type of battery, and to some extent, |
| generators also draw reverse current when they | | | | the experience and philosophy of the system |
| stop. In most controllers, charge current passes | | | | designer or operator. Some controllers have |
| through a semiconductor which acts like a valve | | | | adjustable set points, while others do not. |
| to control the current. It is called a | | | | Manage Set Points vs. Temperature: |
| "semiconductor" because it passes current only in | | | | The ideal set points for charge control vary with |
| one direction. It prevents reverse current without | | | | a battery's temperature. Some controllers have a |
| any extra effort or cost. In some controllers, an | | | | feature called "temperature compensation." When |
| electromagnetic coil opens and closes a mechanical | | | | the controller senses a low battery temperature, |
| switch. This is called a relay. The relay switches | | | | it will raise the set points. Otherwise when the |
| off at night, to block reverse current. If you are | | | | battery is cold, it will reduce the charge too soon. |
| using a PV array only to trickle-charge a battery, | | | | If your batteries are exposed to temperature |
| then you may not need a charge controller. This | | | | swings greater than about 17degrees c, |
| is a rare application. An example is a tiny | | | | compensation is essential. Some controllers have a |
| maintenance module that prevents battery | | | | temperature sensor built in. Such a controller must |
| discharge in a parked vehicle but will not support | | | | be mounted in a place where the temperature is |
| significant loads. You can install a simple diode in | | | | close to that of the batteries. Better controllers |
| that case, to block reverse current. A diode used | | | | have a remote temperature probe, on a small |
| for this purpose is called a blocking diode . | | | | cable. The probe should be attached directly to a |
| Stopping Overcharge: | | | | battery in order to report its temperature to the |
| When a battery reaches full charge, it can no | | | | controller. An alternative to automatic |
| longer store incoming energy. If energy continues | | | | temperature compensation is to manually adjust |
| to be applied at the full rate, the battery voltage | | | | the set points (if possible) according to the |
| gets too high. Water separates into hydrogen and | | | | seasons. It may be sufficient to do this only twice |
| oxygen and bubbles out rapidly. There is | | | | a year, in spring and autumn. |
| excessive loss of water, and a chance that the | | | | Manage Set Points vs. Battery Type: |
| gasses can ignite and cause a small explosion. The | | | | The ideal set points for charge controlling depend |
| battery will also degrade rapidly and may possibly | | | | on the design of the battery. The vast majority |
| overheat. Excessive voltage can also stress your | | | | of renewable energy systems use deep-cycle |
| loads or cause your inverter to shut off. | | | | lead-acid batteries of either the flooded type or |
| Preventing overcharge is simply a matter of | | | | the sealed type. Flooded batteries are filled with |
| reducing the flow of energy to the battery when | | | | liquid. These are the standard, economical deep |
| the battery reaches a specific voltage. When the | | | | cycle batteries. |
| voltage drops due to lower sun intensity or an | | | | Sealed batteries use saturated pads between the |
| increase in electrical usage, the controller again | | | | plates. They are also called "valve-regulated" or |
| allows the maximum possible charge. This is called | | | | "absorbed glass mat," or simply |
| "voltage regulating." It is the most essential | | | | "maintenance-free." They need to be regulated to |
| function of all charge controllers. The controller | | | | a slightly lower voltage than flooded batteries or |
| "looks at" the voltage, and regulates the battery | | | | they will dry out and be ruined. Some controllers |
| charging in response. Some controllers regulate | | | | have a means to select the type of battery. |
| the flow of energy to the battery by switching | | | | Never use a controller that is not intended for |
| the current fully on or fully off. This is called "on | | | | your type of battery. |
| off control." Others reduce the current gradually. | | | | |