Charge Controllers For Solar Installations

Charge controllers control the charge reaching your batteries there by prevent the batteries from getting damaged due to overcharging.

Most quality charge controller units have what is known as a 3

stage charge cycle that goes like this :

BULK

This is the very first stage of the charging process and it is characterized by  Current  being sent to batteries at the maximum safe rate. This process continues until the battery is about 80-90 % fully charged. Voltage at this stage typically range from 10.5 volts to 15 volts.

ABSORPTION

This is the second stage of the battery charging process. At this stage, the Bulk Voltage is maintained for a specified period of time and current gradually tapers off as internal resistance increases as a result of the charging up of the batteries.

FLOAT

 As soon as the batteries become fully charged, the voltage is lowered to float level (usually 13.4 to 13.7 volts) to prevent over-charging which could lead to battery damage. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging

A charge controller that is worth it should at-least be a pwm controller.But if you want to maximize the power from your solar panels then i suggest you go for an mppt charge controller.

Mppt stands for maximum power point tracking. which could be defined as the point on the current-voltage (I-V) curve of a solar panel, where the product of current and voltage is equivalent to maximum wattage.

Hence Maximum Power Point Tracking (MPPT) is a charge controller technique that attempts to supply maximum power to the batteries by tracking the maximum power point (MPPT) at all times thereby achieving a 15% to 35% increase over other types of charging techniques.

A normal charge controller charges your battery bank at battery voltage irrespective of its rated output. for example, a 200w panel rated at 32v, 6.25a charging a 24v battery bank, will supply 24v*6.25a = 150watts. but your panel is supposed to be 200w, so (200w-150w) that then means that you are goin to loose 50w on any given day regardless of how bright the sun is in the sky.

it even gets worse if your battery voltage is low, assuming you used your batteries heavily overnight and your  battery bank voltage dropped to about 18v, in the morning when the sun comes up,your panels will only be outputting 18v*6.25a = 112.5watts. hence you lose about 87.5watts! suddenly your 200w panel is only as good as a 100w panel, half what you paid for!

Now, with an mppt solar charge controller, the charge controller looks at the output of the panels, and compares it to the battery voltage. it then figures out what is the best power that the panel can put out to charge the battery. it takes this and converts it to best voltage to get the maximum current into the battery.

Most modern mppt's are around 93-97% efficient in the conversion. you typically get a 20 to 45% power gain in cloudy weather and 10-15% in bright sunlight.

for example, assuming you use a 200 watts solar panel and your battery is currently low, at 24 volts. an mppt controller takes that 32volts at 6.25amps and converts it down, so that what the battery gets is now 8.33 amps at 24 volts. which means you will still end up having approx 200w power

24v*8.33 = 199.92 approx 200w.

assuming your battery bank voltage is low, it even gets better:

18v*11.1 = 199.8 approx 200w

unlike the normal charge controller where you lose power as your battery voltage reduces,
with an mppt charge controller, he exact opposite is the case.

when thinking about purchasing a charge controller, you don't just think of the present, i feel you need to give allowance for future expansions, so that when that time comes, you don't have to start thinking of buying another charge controller.

Atleast a 60amp charge controller should be able to serve an average home with some room for future expansions.

Charge controllers have an adjustable voltage system which can be changed to sooth the voltage system you are using, be it 12,24,48 volts.

Just Like Inverters, Charge controllers can also be stacked and connected in  parallel which increases the overall current while the voltage remains constant or in series to increase the overall voltage while the current remains constant. So even if you bought a charge controller which became undersized as time went on, you could consider buying another one of the same brand and capacity and then stacking them together.