In General:

 

 

What does a charge controller do

 

 

 

 

 

A charge controller, is like the voltage regulator in your cars alternator.

It regulates the voltage and current coming from the solar panels to the battery.

 

 

 

 The primary job of the Solar charge control is to prevent battery overcharge.  If your solar array were connected directly to the battery without a controller, battery life would be severely reduced. 

 

 When charging lead acid batteries the first 70 - 80 % of capacity is easily accepted and does not require a controller, but as the battery approaches a full state of charge the current must be controlled. This is where the three or four stage controller comes in.

I. The first stage, called BULK, lets 100% of the available power into the battery when the voltage is low. As the battery voltage climbs upward to the bulk voltage set point the controller goes into the second stage.

II. The second stage, called ABSORPTION, starts to taper the current by switching the array on and off at a very fast rate.  This ultra fast switching  is called Pulse Width Modulation. After the battery has been at the absorption mode for a set time limit the controller goes into the third stage of the controlling process.

III. The third stage is called FLOAT.  When in the float mode the controller turns the array off more than on to keep the battery at a full state of charge without overcharging or causing the battery to use an excessive amount of water.

VI. The fourth stage, called EQUALIZE and performs a controlled overcharge. It allows the battery voltage to rise to a user selected voltage which is usually 1 - 1.5 volts higher than the bulk voltage. When the battery reaches this higher voltage the controller will hold the set voltage for a user selected amount of time. Many of today's controllers will perform this automatically once a month.

 

 Charge controls come in all shapes, sizes, features, and price ranges. They range from a  small 4.5 amp control, up to the Heliotrope controls in the 300 Amp range.12, 24, 48VDC.

 

 Most controllers come with some kind of indicator, either a simple LED, a series of LED's, or meters - on many these are options. The simplest usually have only one or a couple of small LED lamps, which show that you have power and that you are getting some kind of charge. 

 

 Most of those with meters will show both voltage and the current coming from the panels and the battery voltage. Some also show how much current is being pulled from the LOAD terminals.

 

 

 

What is a PWM controller?

 

 Quite a few charge controls have a "PWM" mode. PWM stands for Pulse Width Modulation. PWM is often used as one method of float charging. Instead of a steady output from the controller, it sends out a series of short charging pulses to the battery - a very rapid "on-off" switch. 

 

The controller constantly checks the state of the battery to determine how fast to send pulses, and how  long (wide) the pulses will be. In a fully charged battery with no load, it may just "tick" every few seconds and send a short pulse to the battery. In a discharged battery, the pulses would be very long and almost continuous. The controller checks the state of charge on the battery between pulses and adjusts itself.

 

 

MPPT (Maximum Power Point Tracker)

 

- for an extra 25% output from your panels). Those have complete computer interface, communications, and data logging built in. These are rather expensive, and can usually only be justified on systems with 300 watts or more of solar panel. 

 

 These MPPT charge controls, ( SEC, Outback, RV Power, Apollo and such) used with a panel tracking system, such as the Zomeworks, can total up to nearly a 40% year around gain in systems.

 

 

Pictured below one of our home 48V arrays at peak power:  Solar Panel Current: 19.9A. Output charge Current: 26,2A

 

 

 

That means 6.3A or 32% more. That's what we call significant!

 

 

 

 Some controllers also have a "LOAD", or LVD output, which can be used for smaller loads, such as small appliances and lights. If you have any questions about charge controllers call us at (306) 298-2088 or e-mail us.