Solar panels cannot directly charge a battery. To get chaotic energy from the sun into usable energy for your batteries you need to use a charge controller. Most ’12 Volt’ solar panels produce around 16-20 Volts when in direct sunlight. Batteries are finicky, and if they get too much voltage they get stressed and damaged.
A charge controller regulates this. Charge controllers can also keep track of roughly how much power is currently in the battery for smart charging cycles.
Standard Charge Controllers (PWM) vs MPPT Charge Controllers
- PWM: Pulse Width Modulation. When a solar panel produces 18v of electricity, the charge controller has to convert that to a safe 13.8V that is healthy for the batteries. This type of charge controller will effectively throw any voltage above 13.8V away so you lose some of the energy produced. PWM technology is simple and has been used for decades in solar system installs. Cheaper and less internals to break.MPPT: Maximum Power Point Tracking. This uses electrical wizardry to change the input Volts to match the needed output without having to throw much energy away. For example, if your panels are producing 18V at 6 Amps, the charge controller will adjust this by dropping the Volts to 13.8 and increasing the Amps to something like 7. Your batteries get most of the available power from increasing the amps this way.
Because MPPT controllers can accept higher voltage input, they offer benefits when wiring multiple panels together
There are two ways to wire panels together: series and parallel. We cover that more in our solar panel basics article. If you have a PWM controller, you don’t have much choice but to wire in parallel. This means you have more Amps which needs combiners, fuses, and bigger wires. All of these things cost more money and time to install. If you have an MPPT controller, you can wire multiple panels in series to input higher voltage and let the controller figure it all out. No fuses, combiners, or oversized wires needed.
If you ever come across an inexpensive charge controller that says something like “MPPT simulating”, it’s just a PWM in disguise. There’s no way to make the internal electronics cheap.
For some further reading and cool graphs, check out this article by mozaw.com.
How To Size Your Campervan Charge Controller:
At least 7.5 Amps for every 100W of solar
This is easier for campervans because we already know our batteries are at 12V. Vandwellers are not usually using above 1000W of solar, so use the above for a good rule of thumb. Going bigger isn’t an issue with this, other than price, and allows you to add more panels later if your setup proves to not be enough.
Installing A Charge Controller
First and foremost, always connect the solar panels last. You don’t want current running into the controller with nowhere to go! Read the instructions for your specific controller, but here is what to generally expect:
- Install the controller as close to the batteries as possible with enough of a gap for heat ventilation. This reduces current loss. It also helps with controllers that have an internal temperature sensor to have an accurate estimate of battery temp for proper charging.
- Don’t install a charge controller above the batteries. You don’t want any off-gassing to disturb the controller’s electronics.
- Make sure to fuse the (+) wire close to the battery so any system short doesn’t start a fire.
- If the charge controller has an external ground (chassis ground) terminal on it, you should run a separate wire from this directly to the vehicle chassis. This subject gets really complicated to understand as a vehicle is different from most other types of electrical systems. Follow your instruction manual, which will most likely say to do it this way. The basic reasoning for this is that if there is an internal fault (broken bit inside the controller) then electricity still has a path back to the battery to properly pop the fuse.
What Is A Charge Controller Load Output (LVD)?
Most charge controllers have three sets of terminals. One set goes to battery. One set goes to panels. Self explanatory. Then the third set usually says LOAD or LVD. This output is designed to be a level of battery protection and there are two schools of thought on this. But first, where do these wires go?
The load output is meant to power all of your small electronic gizmos through the charge controller. So you’d have the (+) wire run to a DC fuse box that is connected to your lights, refrigerator, usb chargers, etc. And the (-) wire connects to a bus bar for the return wires of all these gizmos. If the batteries drop below a certain voltage, the charge controller will cut power to to the fuse box to protect your batteries from being drained further. Some smart charge controllers will adjust this voltage cutoff if your batteries aren’t getting full charge daily. This is how wiring to the load terminals looks (fuses omitted):
We don’t find the benefits of this feature all that helpful. Instead, you can wire your fuse box directly off of the batteries, as shown below (fuses omitted):
Both ways are just as safe and easy to wire, so you can choose to do it however you wish. Here are the reasons we like it better without the load terminals:
- The charge controller load terminals only work for small powered items. You will not be able to run an inverter through them. So you will usually have things that can drain the battery even if the charge controller cuts them off, which makes the battery cutoff less effective.
- Having power cut to certain items is inconvenient. We have used the load terminals before and having your lights switch off as you’re cooking dinner is alarming and annoying. Because the cutoff is at a 50% battery level, we would have preferred to run the batteries to 45% and get extra power the next day to make up for it. Plus, it feels weird to not have your fridge running when it should be.
- You will always be nearby your solar system, so a simple voltage display in the van will allow you to monitor the battery charge yourself and adjust your electrical usage. It puts you a bit more in charge and you can often predict and adjust well in advance of needing a battery cutoff.
- Larger electronics such as inverters and fridges usually have their own low power cutoff for when the batteries get really low, so you won’t likely kill them without using the charge controller load terminals.
Recommended Charge Controllers
|Charge Controller Recommendations||Size||Max 12V Solar Capacity|
|PWM Charge Controller||10A||100W|
|MPPT Charge Controller||20A||260W|
|MPPT Charge Controller||60A||860W|