We all know about charge controllers, and there are two types, PWM and MPPT, These take the power produced by the solar panel and changes that to charge a battery.
There are a lot of fake charge controllers and there are the costly controllers, but you can built your own.
Single panel and Simple.
Solar panels produce around 37v and have a mppv of around 30v.
The current of the panel is around 8 amps.
Understanding.
Ohms law, conservation of energy and Power factoring. come into effect when looking at building a controller, you must be able to handle the power.
Voltage on solar will happen easy, the hard part is the current which comes from sunlight (intensity).
V x I = W and in English, voltage (V) multiplied by amps (I) which gives you the W (power)
When we change the voltage, as we step up that voltage the current lowers, and when we lower the voltage the current rises. The Maximum power point (MPP) is where W is the highest, with variation to the voltage and current.
Power factors (factoring)
Many charge controllers, will have a voltage limit and a current limit. the voltage limit is the input voltage from the panels, the current limit is usually the output current. Some times there is also a input limit shown or you have to do the math.
If we have a solar panel with 35Voc and a current of 5 amps, if we then have a 12v battery we will know the current output. Lets do some math;
35V x 5A = 175W
if we have a 12v battery, the controller will buck the voltage to 12v.
So to find the factor, we divide the voltage in by the voltage out, in this case 35/12 = 2.917
We then take the current ( using the peak current of the panel for hardware specifications) in this example we are using 5 amps.
We now know that the output current will be 5 x 2.917 = 14.583
The energy remains the same, in this case 14.583 x 12 = 175W. In the real world there are losses to the power in the conversion, maybe 10% or maybe 3%. There is always losses in converting power, even when we convert energy into chemical energy in the battery.
Building a charge controller.
A charge controller consists of a few parts, the charge and the control. – thats solved the naming...
Firstly we take a buck converter which will take the voltage and current of the panel and give us the right “stuff” to charge the battery.
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On the charger, we set the voltage and the current to the maximum of the panel as set out on the sticker as MPPV and MPPI. We set this using a multimeter, we then connect to the controller.
The controller is responsible for the battery, when its charged and when it needs charge and the parameters should be set to match your battery.
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We have to use an SSR to make the switch work, as the controller itself cannot handle the current, the controller is designed to switch on a mains powered charger, the mains charger is changed to a control voltage so that the controller will switch on and off the SSR only which is feeding the solar DC from the charger to the battery.
Input, is the control voltage, the battery is to the ssr and the monitor goes to the battery.
The charger output goes to the SSR input and the SSR output goes to the battery, the ground (negative) goes from the charger to the battery (direct).
We now have a solar charge controller. but before we make connections we must test each time to ensure that we are getting it right. and now you have built and checked, you may want to add a display to show the charge voltage and current. you can check out of battery monitor project for a more “hands on” or we offer a simple battery monitor that you put inline with the cables to the battery or on the solar side depending what readings you want to have.
If you want to see how effective your charge controller is, installing a meter before the charger and before the battery will have a difference. The smaller the difference the better it is.
Remember to calibrate and adjust, some items will not be 100% accurate, so we need to test them and make adjustment to correct them. if your tested meter reads 12v but the control is 11.4v the setting voltage for 12v would be 12.4 to compensate.
How is it working?
Your panel will provide a voltage and a current, the charger will take the power and lower the voltage to the battery voltage.
When it is doing its thing, the panel voltage will go to the maximum power point.
The charger will convert the voltage for the battery and boost the current as its lowering the voltage.
When the charge controller wishes to charge the battery the circuit is made, the power from the charger flows to the battery, the controller reads the voltage of the battery and when the battery is charged it will turn off.
Can I charge two batteries or divert the power when it is not charging?
Yes.
On relays there are three ports, they are normally open, normally closed and common.
The common is the input. When we give it power to switch, it goes from normally closed to normally open, giving two paths where you can have your controller switch on the charging when it needs it and the other port will be powered when the controller switches off.
There we see a normal relay, ports 87 and 87a are the two paths. 86 and 85 are the switch control wires, that control the relay. 30 is the common, here this would be the power from the charger. 87 would go to the battery and 87a would go else where when the controller is off.
Caution!!!!
When switching a DC circuit, there is a lot of power flowing which will arc. if you are using the other port to power devices and the controller switches under a full load you may damage the SSR or cause wear.
all DC switching is subject to this as it is more ideal to lower loads before switching. for battery charging as the battery reaches full charge, the current (load) is lower and therefore should NOT be an issue.
The shift of the stress load will be on the DC capacitors on the input.
Can I add more panels?
Depending on the panel that you are using, you can add panels only to the limit of the hardware, we do not recommend running hardware at its limits.
Can I add more of these CC?
no, these are not isolated, therefore you cannot add more without additional work. do not connect more to the panels or the battery as this will cause problems.