Solar Charge Controllers; everything you need to know

Solar panels have come in leaps and bounds over the last two decades, and in the camping and 4WDing world its completely changed the way people travel and enjoy themselves.

A good solar panel and battery setup will allow you to run anything from fridges through to lights, water pumps and even inverters running normal 240V appliances like you would at home.

In todays post, we are looking at what a solar charge controller is, what you need to know about them and what your options are. Please know this is all referring to 12V applications, and not inverters for household use!

To clear up any confusion, these are often referred to as Solar Regulators as well; its the same thing; it controls, or regulates the charge to your battery.

What is a solar charge controller?

In the camping and 4WD world, almost all batteries are 12V. This means they need to be charged at a rate that is around 12 – 14.5 volts, depending on the battery type.

No solar panels output at this rate, and so you need a solar panel regulator to convert the higher voltage into something suitable for your battery.

Why do you need one?

You need a solar charge controller to charge your batteries. Without one, you’ll fry your batteries in no time. It would be similar to putting petrol in a diesel motor; its not something you can be flexible with.

What options are there for solar charge controllers?

There’s a lot of different types of solar regulators that you can purchase and use, and they will vary in price and ability dramatically.

You can buy a cheap PWM regulator for $30, or a high end battery management system and DCDC for upwards of $800. 

The choice is yours, and you don’t need to spend huge money, but getting something that suits what you need is important.

PWM

The cheapest solar regulator is going to be a PWM, or pulse width modulation charger. These just step the power down in the most simple way, and are a great, economical way to charge your batteries.

MPPT

The next step up is MPPT, or maximum power point tracking, which is a bit smarter in the way it converts the power, and you’ll generally see better results.

It’s hugely important to know that a lot of solar regulators you purchase on eBay are labelled as MPPT, and are actually not.

Much like many of the solar panels are incorrectly advertised, you need to be very careful. Keen to know more? Check this out – eBay solar panels.

A lot of people end up with an MPPT solar regulator, as they do a great job. These are stand alone solar regulators.

DCDC with solar input

If you have the ability to charge your batteries from your vehicle as well, a lot of people are going down the DCDC charger route, with a solar input.

These will take alternator power and charge your batteries, or they will take power from your solar panels and charge the batteries that way.

Its important to ensure that your DCDC will tolerate the voltage from your panels, as some are higher voltage and will damage the charger. Not everyone needs a DCDC though, and if you are considering one, have a read of this; What is a DCDC charger and do you need one?

Factory solar regulators stuck onto the panel

You’ll see a lot of cheaper solar panels that come with regulators will have them stuck onto the back of the panel.

We have a Rich Solar folding panel that we carry around like this, and its done a decent job over the years. However, its not a good idea to have the regulator stuck onto the back of the panel for a number of reasons.

Cables suffer voltage drop, and you really want your solar regulator as close to the batteries being charged as possible. If its a long way away (like when its stuck to the solar panel), you’ll find that by the time the current gets to your battery its lost some of its strength.

Electrical components should be kept cool and out of the weather as much as possible, and if you’ve ever put your hand on a solar panel in the middle of the day you’d know that they are anything but cool and out of the weather!

Ideally, you run the unregulated cables to a nicer environment near your batteries, and let them do the charging from there. That said, if it works, it works and you don’t have to change anything.

Panel sizes and wattage

Solar panels come in a huge range of sizes and wattages. You can get the normal 12V panels (18V input), or they can be 36V (like what you have on the roof of your home). Your solar panel size should suit your setup, and ensure your batteries stay healthy.

More importantly, the voltage needs to match your solar charger, as a huge number of solar controllers will not take higher wattage panels.

One of the most common ways to set up a cheap solar system is to use old house solar panels that you can literally pick up for under $30 each, and feed them into a solar controller that will take the higher voltage and convert it down to charge a 12V panel.

MC4 vs Andersons

A large majority of panels purchased today come with MC4 connectors. These are a black, round, plastic fitting that works pretty well (although many are fakes).

The alternative is to use Anderson plugs, which are very well known and work well. MC4 connections should be waterproof, whereas Andersons can get wet and remain unaffected. 

Anderson plugs are probably easier to work with, but both do the job just fine. It is worth knowing that if you cut your MC4 connectors off you can probably say good bye to any warranty that you have, and that it is possible to get MC4 to Anderson plug adapters.

Parallel or series

If you have more than one solar panel, you’ll have to decide how to link them up. The most common way  is in parallel, resulting in 18V coming from the panels, but double the wattage.

For example, you could have two 100 watt solar panels, and you’d get 200W coming in at 18V. If you wire them up in series, you’d get 100W at 36V.

How you wire them up depends on your exact system and the solar controller that you are running, but you are best off sticking with Parallel unless you have reason to change. There are some pro’s and con’s to each, but parallel is far more common.

Cable sizing

Like anything electrical, you need to ensure that the cable length and size is suitable for your setup.

If you have a significant solar system, you’ll need decent thickness cables to ensure there is limited voltage drop and to ensure that you don’t start a fire with the cables getting too hot.

There’s a number of voltage drop calculators around, where you can put the amperage going through them and the cable run length, and get the correct cable size for the job. Don’t undersize it; its just not worth it.

Battery type

Most solar regulators are set up to charge your standard lead acid battery, and are not able to correctly charge lithium.

If you have a lithium battery, you need to ensure that the solar charger has a lithium charging profile, as its got different voltages than your normal lead acid.

Yes, you can use a traditional lead acid charger to charge a lithium; its not going to blow it up if the voltages are not too high but its inefficient, and not the right way to go about it. Drop in lithium batteries are a bit misleading in this way. More to come on that on another post.

The regulator voltage needs to suit the charger

When designing a system, you should ensure that everything is compatible. What I mean by this, is that the solar panel voltages vary, and not all chargers will take all voltages. For example, house panels, and even some high wattage panels designed for 12V will not work through a number of regulators. 

A lot of chargers will not take a current of over 28V, and there’s plenty of panels that exceed this, so check carefully before you commit to any parts.

Using two solar regulators

I often see people asking whether they can more than one solar regulator into their batteries. For example, if you had a 100W panel with a regulator on it, can you connect that to a battery that is also receiving charge from a DCDC via solar, or a different regulator?

The answer is yes, you absolutely can, and you won’t do any damage. How it behaves will be determined by the regulators, and they can reduce the overall efficiency when working with each other, but they will both put charge into your system.

We’ve done this many times, and our Reconn R2 is actually wired up with an Enerdrive DCDC being fed by alternator power from our 4WD and a 120W panel on the roof, and then 600W of panels feeding a Renogy Solar controller.

They both feed our 340aH of lithium batteries and we have no issues with them.

Of course, you can read more about this here – can you run two controllers into the same battery?

What have we missed? What else do you want to know about solar charge controllers?

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