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All About Solar Charge Controllers - Types & Installation

There is some confusion about solar charge controllers and which one to pick for your particular needs. This article takes you through the different types of solar charge controllers and shows you how to install them.

 

There are two main types of solar charge controllers. There is the lower priced PWM (pulse width modulated) solar charge controller and the MPPT (maximum power point tracking) solar charge controller.

 

Solar Charge Controller

 

Pulse Width Modulated Solar Charge Controllers

 

The PWM solar charge controller is lower on the price scale. These are the standard and most commonly seen solar charge controllers. These pulse the solar panel output to the battery bank and disconnect the solar panels when the batteries are topped off.

 

The quality of these vary but it is hard to tell on the outside. You want a solar charge controller that will condition the batteries and help maintain them properly for a longer life. The cheap solar charge controllers simply connect the solar panels until the battery reaches a certain voltage and then disconnects them. The better solar charge controllers will take the batteries through all the stages that they need for long life.

 

These stages are the bulk charge, absorption charge and float mode. You can read my previous article on battery charging and voltages here: All About Batteries - Charging - Maintenance - Voltages

 

When buying any solar charge controller the best thing you can do is to get the most expensive on that you can afford. Read reviews on the product before you buy it. Unless you are working on some small solar power project and now your home or garage then do not buy the cheaper solar charge controllers at all.

 

 

 

In the video linked at the end of this article I show you two PWM solar charge controllers from Harbor Freight. One is a bit more expensive and is heavier. This one costs between 60 to 80 dollars and has some cooling fins on the back side. I would think, at first glance, that this is a better quality solar charge controller from the heft and looks of it. The other one is larger in size but this is unusual. Generally the cheaper solar charge controllers are actually smaller. In this case it is only larger because it has a lot of fancy outputs and connections on it. This is why I keep these around. I like to use the different voltage outputs.

 

Maximum Power Point Tracking Solar Charge Controllers

 

MPPT solar charge controllers are better for your solar power system in a couple ways. They are higher quality in the first place and generally most will also condition your batteries and go through the multiple stages of charging. But MPPT solar charge controllers also give you more solar power from each solar panel.

 

They are able to do this by matching the voltage of your solar panels to the battery bank. First, lets see why this helps.

 

With a cheaper solar charge controller or PWM solar charge controller the power output from the solar panels is simply connected to the battery bank until they are full and then removed. A lead acid battery will take any current in its voltage range and ignore any excess. This means that if you put 15 volts into a 12 volt battery, the battery will ignore anything above its 12 volts. The rest is lost.

 

Most 12 volt solar panels are rated to put out about 18 volts or so. This is done so that you can get more charging output in varying sunlight intensities. But with a PWM solar charge controller anything above the battery voltage is ignored. This is wasted energy.

 

An MPPT (Maximum Power Point Tracking) solar charge controller will actually step the voltage up or down to match that of the battery bank. This will give you the maximum amount of charge from your solar panels at any given time. If you are in low light conditions the MPPT solar charge controller will step up the lower voltage to match that of your battery while reducing the available current a bit. Power cannot be changed. Power (Watts) = Voltage times Current (Amps).

 

W = V x A

So by increasing the voltage of the output you are reducing the current. The advantage is that you are still putting some charge into the battery bank whereas a cheaper PWM solar charge controller would disconnect the solar panels at this time.

 

When the sun is shining brightly and the solar panels are producing their maximum output power then the MPPT solar charge controller will reduce the voltage output to the batteries and increase the current. This gives you maximum output to the batteries. With a PWM solar charge controller all this excess power would be lost. It would be simply ignored by the batteries.

 

A Maximum Power Point Tracking solar charge controller will also check the temperature of the battery bank at any given time to ensure that the voltage shows is the actual charge status of the batteries. A battery voltage will vary with a change in temperature so this is not the best way to check battery charge status.

 

Now an MPPT solar charge controller gives you one more huge advantage over a PWM solar charge controller. The MPPT solar charge controllers allow you to string up a series of solar panels to increase their overall voltage. This reduces loss in the wires. Its too much to go into at this time but lower voltage in a wire increases the energy lost in the wires over longer distance. By increasing the voltage going through the wires you can use smaller wires and have less loss in the lines. Smaller wires means cheaper installation cost up front.

 

The MPPT solar charge controllers are generally rated at 24 volts, 48 volts on up to around 130 volts input. This means that you can connect multiple solar panels in series. When you connect solar panels in series you are increasing their output voltage. Two 12 volt solar panels in series gives you 24 volts output. Just add the totals together to get your output voltage.

 

In this way you are gaining much more power into your batteries for any given weather and sunlight conditions.

 

Current and Watts

 

When buying a solar charge controller, not matter if it is a PWM or an MPPT solar charge controller, you have to know about amps and watts. Most solar charge controllers are rated in Watts. But some only show Amps.

 

To know what you need, you will have to do a little bit of math. For this article we will keep it simple but in a future article we will go into amps, watts and volts more deeply and how to select and match up your system for your needs.

 

But for know simply know that Watts = Amps x Volts.

 

If a solar charge controller is rated at 10 amps and 12 volts then it can handle a maximum of 120 watts of solar panels. 10 A x 12 V = 120 W.

 

If your solar charge controller is rated at 120 Watts then you know that this is the maximum size solar panel you can use.

 

Buy a solar charge controller that is rated for more than you plan to use so that you have room for expansion later.

 

Connecting Solar Charge Controllers

 

Connecting a solar charge controller is relatively easy. Most solar charge controllers have three sets of input wires. There is the battery connection. There is the solar panel connection. And generally there is the output section.

 

Always first connect the batteries to your solar charge controller before anything else. If you do not connect the batteries to the solar charge controller first then you run the risk of damaging the solar charge controller.

 

Next connect the solar panels to the solar charge controller solar panel terminals.

 

And finally, if you want, you can connect your load (devices you are powering) to the solar charge controller. I never use this connection myself because I prefer to keep an eye on the level of my batteries manually. This output will shut off power to your devices if the voltage in the battery gets too low. This will protect your battery bank from damage. If you prefer not to worry about the voltage in the battery yourself then use this output. But never connect anything larger than the rated output of the solar charge controller.

 

I always connect the load (devices) to the battery bank myself with a fuse inline. This allows me to pull all the power I need at any given time without being limited by anything but the wires and the battery capacity.

 

Again this means that you will have to keep an eye on your solar battery bank voltage manually to ensure that you do not drain them too low and cause damage.

 

Combining Solar Charge Controllers

 

You can always expand your solar power system later by adding more solar charge controllers. You do this by simply adding a solar charge controller in parallel with the others. There is no harm in using different makes and models of solar charge controllers but you will have the best output if they are the same make and model.

 

Try not to pair up PWM and MPPT solar charge controllers in the same system. This would be wasteful.

 

When mixing solar charge controllers from different manufacturers, they will work but you will have losses in the system. Different manufacturers have different settings so one solar charge controller may be pumping out the power while another is just sitting there because the first one has a slightly higher voltage output than the other. This little difference will mean you lose output power overall.

 

Try to match up your solar charge controller and stick with one type for best results.

 

Summary

 

In conclusion always buy the most expensive solar charge controller that you can afford. Also get one that is rated higher for your needs in order to allow for future expansion.

 

If you are on a budget then the PWM solar charge controllers will get you started with a solar power system. But if you want to go for real power and maximum energy output then use MPPT solar charge controllers.

 

Always read reviews before buying any solar charge controller to make sure you do not get cheated. There are many fakes out there so be careful and do your research.

You can watch today's video here: All About Solar Charge Controllers ~ Types ~ How To Install

 

While you are over there please subscribe to my YouTube channel and follow our daily videos as we strive to become self sufficient and off the grid on a budget.





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Troy Reid

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