This is the Sunny Buddy, a maximum power point tracking (MPPT) solar charger for single-cell LiPo batteries. This MPPT solar charger provide you with the ability to get the most possible power out of your solar panel or other photovoltaic device and into a rechargable LiPo battery. Set-up is easy as well, just plug your solar panel into one side of the Sunny Buddy and your battery into the other and you are good to start charging!

The output of the Sunny Buddy is intended to charge a single polymer lithium ion cell. The load should be connected in parallel with the battery. By default, the Sunny Buddy comes set to a maximum charge current of 450mA with a maximum recommended input of 20V (minimum 6V). It’s recommended that batteries not be charged at greater than their capacity rating; thus, the smallest battery that should be charged with the Sunny Buddy is 450mAh.

Each Sunny Buddy comes equipped with a LT3652 power tracking 2A battery charging circuit and pre-installed barrel jack and 2-pin JST connectors with unpopulated areas to install your own personal 3.5mm screw terminals for added input/output options. This revision also adds a potentiometer to the input to set the holding voltage for MPPT and we've also tweeked the feedback resistors on the output to change the float voltage.

A battery charger, or recharger, is a device that stores energy in a battery by running an electric current through it. The charging protocol (how much voltage or current for how long, and what to do when charging is complete) depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging (i.e., continued charging after the battery has been fully charged) and can be recharged by connection to a constant voltage source or a constant current source, depending on battery type. Simple chargers of this type must be manually disconnected at the end of the charge cycle. Other battery types use a timer to cut off when charging should be complete. Other battery types cannot withstand over-charging, becoming damaged (reduced capacity, reduced lifetime), over heating or even exploding. The charger may have temperature or voltage sensing circuits and a microprocessor controller to safely adjust the charging current and voltage, determine the state of charge, and cut off at the end of charge.

Chargers may elevate the output voltage proportionally with current to compensate for impedance in the wires.

A trickle charger provides a relatively small amount of current, only enough to counteract self-discharge of a battery that is idle for a long time. Some battery types cannot tolerate trickle charging; attempts to do so may result in damage. Lithium-ion batteries cannot handle indefinite trickle charging.

Slow battery chargers may take several hours to complete a charge. High-rate chargers may restore most capacity much faster, but high rate chargers can be more than some battery types can tolerate. Such batteries require active monitoring of the battery to protect it from overcharging. Electric vehicles ideally need high-rate chargers. For public access, installation of such chargers and the distribution support for them is an issue in the proposed

Charge and discharge rates are often given as C or C-rate, which is a measure of the rate at which a battery is charged or discharged relative to its capacity. The C-rate is defined as the charge or discharge current divided by the battery's capacity to store an electrical charge. While rarely stated explicitly, the unit of the C-rate is h?1, equivalent to stating the battery's capacity to store an electrical charge in unit hour times current in the same unit as the charge or discharge current. The C-rate is never negative, so whether it describes a charging or discharging process depends on the context.

For example, for a battery with a capacity of 500 mAh, a discharge rate of 5000 mA (i.e., 5 A) corresponds to a C-rate of 10C, meaning that such a current can discharge 10 such batteries in one hour. Likewise, for the same battery a charge current of 250 mA corresponds to a C-rate of C/2, meaning that this current will increase the state of charge of this battery by 50% in one hour.[5]

Since the unit of the C-rate is typically implied, some care is required when using it to avoid confusing it with the battery's capacity to store a charge, which in the SI has unit coulomb with unit symbol C.

If both the (dis)charge current and the battery capacity in the C-rate ratio is multiplied by the battery voltage, the C-rate becomes a ratio of the (dis)charge power to the battery's energy capacity. For example, when the 100 kWh battery in a Tesla Model S P100D is undergoing supercharging at 120 kW the C-rate is 1.2C and when that battery delivers its maximum power of 451 kW, its C-rate is 4.51C.

This unit charges batteries until they reach a specific voltage, then trickle charges them until disconnected.

All charging and discharging of batteries generates internal heat, and the amount of heat generated is roughly proportional to the current involved (a battery's current state of charge, condition / history, etc. are also factors). As some batteries reach their full charge, cooling may also be observed.

Battery cells which have been built to allow higher C-rates than usual must make provision for increased heating. But high C-ratings are attractive to end users because such batteries can be charged more quickly, and produce higher current output in use. High C-rates typically require the charger to carefully monitor battery parameters such as terminal voltage and temperature to prevent overcharging and so damage to the cells. Such high charging rates are possible only with some battery types. Others will be damaged or possibly overheat or catch fire. Some batteries may even explode.[citation needed] For example, an automobile SLI (starting, lighting, ignition) lead-acid battery carries several risks of explosion.

A simple charger works by supplying a constant DC or pulsed DC power source to a battery being charged. A simple charger typically does not alter its output based on charging time or the charge on the battery. This simplicity means that a simple charger is inexpensive, but there are tradeoffs. Typically, a carefully designed simple charger takes longer to charge a battery because it is set to use a lower (i.e., safer) charging rate. Even so, many batteries left on a simple charger for too long will be weakened or destroyed due to over-charging. These chargers also vary in that they can supply either a constant voltage or a constant current, to the battery.

A smart charger can respond to the condition of a battery and modify its charging parameters accordingly, whereas "dumb" chargers apply a steady voltage, possibly through a fixed resistance. It should not be confused with a smart battery that contains a computer chip and communicates digitally with a smart charger about battery condition. A smart battery requires a smart charger (see Smart Battery Data).

Some smart chargers can also charge "dumb" batteries, which lack any internal electronics.

The output current of a smart charger depends upon the battery's state. An intelligent charger may monitor the battery's voltage, temperature or charge time to determine the optimum charge current or terminate charging.

For Ni-Cd and NiMH batteries, the voltage of the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, "delta-V," or sometimes "delta peak" charger, indicating that they monitor voltage change. This can cause even an intelligent charger not to sense that the batteries are already fully charged, and continue charging. Overcharging of the batteries may result. Many intelligent chargers employ a variety of cut-off systems to prevent overcharging.

A typical smart charger fast-charges a battery up to about 85% of its maximum capacity in less than an hour, then switches to trickle charging, which takes several hours to top off the battery to its full capacity

Simple AC-powered battery chargers usually have much higher ripple current and ripple voltage than other kinds of battery chargers because they are inexpensively designed and built. Generally, when the ripple current is within a battery's manufacturer recommended level, the ripple voltage will also be well within the recommended level. The maximum ripple current for a typical 12 V 100 Ah VRLA battery is 5 amps. As long as the ripple current is not excessive (more than 3 to 4 times the battery manufacturer recommended level), the expected life of a ripple-charged VRLA battery will be within 3% of the life of a constant DC-charged battery.