Skip to Content

What Does a Solar Charge Controller Do?

A solar charge controller is a vital piece of a camper electrical system. It is installed between the solar array and the battery bank (or busbars, more often) and regulates the voltage and amperage of the solar array down to a level that is appropriate to charge a battery bank with.

Long story short, the charge controller is essentially a high powered voltage regulator.

Here are the three things we know about charging a battery bank from a solar array:

  • The voltage and amperage of the solar array can be altered depending on how the array is wired.
  • Batteries want to be charged at a very specific voltage.
  • Solar arrays don’t put out a very specific voltage at all.  They can be anywhere from 0 volts at night or upwards of 250V or more depending on the panels used and how the array is wired.

Q: So, how to we charge a battery bank that wants to be charged at a very specific voltage when our solar array puts out an incredibly variable voltage that is potentially much to high to charge a battery bank with?

A: We install a charge controller to regulate the high and variable voltage from the solar array down to a level that is more appropriate to charge a battery bank with. And here’s how it works:

What Does a Solar Charge Controller Do? – Video

Charging a 12V Battery Bank with an 80V Solar Array

A solar array with 4 panels operating at 5A delivered at 20V each, wired with 4 panels in each series-string with 1 series-strings wired in parallel would result in a solar array that operates at 5A delivered at 80V to the charge controller for a total array wattage of 400W (Watts = Amps x Volts).

The Charge Controller will then convert the 80V from the solar array down to the 14.5V that it takes to charge a 12V Battery Bank.  The 400W from the solar array is now being delivered to the battery bank at 14.5V and is therefore charging the battery bank at a rate of 28A (Watts/Volts=Amps).

Charging a 12V Battery Bank with a 40V Battery Bank

A solar array with 4 panels operating at 5A delivered at 20V each, wired with 2 panels in each series-string with 2 series-strings wired in parallel would result in a solar array that operates at 10A delivered at 40V to the charge controller for a total array wattage of 400W (Watts = Amps x Volts).

The Charge Controller will then convert the 40V from the solar array down to the 14.5V that it takes to charge a 12V Battery Bank.  The 400W from the solar array is now being delivered to the battery bank at 14.5V and is therefore charging the battery bank at a rate of 28A (Watts/Volts=Amps).

Effects of a Higher Voltage Battery Bank on the Charge Controller

A solar array with 12 panels operating at 10A delivered at 40V each, wired with 4 panels in each series-string with 3 series-strings wired in parallel would result in a solar array that operates at 30A delivered at 160V to the charge controller for a total array wattage of 4800W (Watts = Amps x Volts).

The Charge Controller will then convert the 160V from the solar array down to the 14.5V that it takes to charge a 12V Battery Bank.  The 4800W from the solar array is now being delivered to the battery bank at 14.5V and is therefore charging the battery bank at a rate of 331A (Watts/Volts=Amps).

Now… This is really too many amps for a single charge controller to handle So… We could either use multiple charge controllers to handle this many watts coming from the array OR we could investigate using a higher voltage battery bank.

Understanding that the wattage from the solar array gets divided by the battery bank charging voltage to get the battery bank charging amps, we can see that as we increase the voltage of the battery bank, the amps charging the battery bank will decrease as the watts stay the same.

WATTS LAW

X

=

0

This would mean that the same array as earlier could be charged by a single 100A charge controller because the increased voltage of the battery bank as decreased the amperage demand even though the charging wattage remains the same.

A solar array with 12 panels operating at 10A delivered at 40V each, wired with 4 panels in each series-string with 3 series-strings wired in parallel would result in a solar array that operates at 30A delivered at 160V to the charge controller for a total array wattage of 4800W (Watts = Amps x Volts).

The Charge Controller will then convert the 160V from the solar array down to the 58V that it takes to charge a 48V Battery Bank.  The 4800W from the solar array is now being delivered to the battery bank at 58V and is therefore charging the battery bank at a rate of 83A (Watts/Volts=Amps).

Charge Controller Operation Calculator

Here is a calculator that you can play around with that will show you how various array configurations and battery bank voltage interact with each other. (This calculator is NOT to be used for accurate sizing of a charge controller as it does not account for max voltages, amperages nor temperature compensation.)

20
5
2
2
12

SOLAR ARRAY

Operating Voltage: V

Operating Amperage: A

Wattage: W

BATTERY BANK

Charging Voltage: V

Charging Amperage: A

Charging Wattage: W

A solar array with panels operating at A delivered at V each, wired with panels in each series-string with series-strings wired in parallel would result in a solar array that operates at A delivered at V to the charge controller for a total array wattage of W (Watts = Amps x Volts).

The Charge Controller will then convert the V from the solar array down to the V that it takes to charge a V Battery Bank.  The W from the solar array is now being delivered to the battery bank at V and is therefore charging the battery bank at a rate of A (Watts/Volts=Amps).

 


Peter Andrrews

Thursday 19th of May 2022

Hi Just discovered your site excellent, I have a DC to DC charger (JayCar 20 Amp) which has a maximum input of 25 volts, to increase volts from solar array is it possible/ practical to use a higher voltage MPPT controller to step higher voltages down for the DC to DC charger. I know this could complicate the system by the DC-DC also automatically connects and disconnects from alternator as required.

Peter for Perth Australia

Chad Brewster

Thursday 21st of April 2022

I have 6 interstate gc2 deep cycle batteries that are connected in series, I think! (I have a diagram I can send?) to a Xantrex Freedom 458 - 2500w inverter. I need to purchase a Charge controller and need to know how to connect it to the batteries? Is one charger enough? Do you recommend a brand for those batteries?

Luke

Monday 11th of April 2022

Quick question for you...I've got a 48v golf cart that I will be putting a lithium (72ah) setup in, and toying with the idea of getting something like an MPP 3048LV to have the additional power available for power tools and such when out in the woods. To get the MPP unit to charge the batteries (just top them off here and there) would I be able to use two 12v panels in series or would that not be enough solar input for the MPP to charge the 48v battery?

I assume two 24v panels in series would be fine, but I'm a bit confined on space based on my use of the cart, unless I built a new/custom roof to hold the larger panels. Just figured I'd ask someone with a lot more time/experience than I'll likely ever have!

Damien Davies

Friday 14th of January 2022

Hello Nate from across the pond, Firstly thanks for all the information and tutorials that you put out via YouTube. I am struggling to understand the settings I should have on my Victron Solar Controller 100/30. The details supplied by the battery manufacturer do not seem to be what the Victron is asking me for. Now that could well be my naive understandings as I am not from an electrical background. Is there a way of understanding what these settings should be? Thanks again for all you do. Kind Regards Damien Davies Lancaster United Kingdom

Jeff Roller

Wednesday 5th of January 2022

I have the Furrion 50A solar charge controller with a 165W Furrion monocrystalline panel. The price of additional panels are too expensive ($500 each) to add many to my fifth wheel. Suggestions for replacement panels that would give a better per watt price to use with this controller?

Nate Yarbrough

Wednesday 5th of January 2022

Mixing and matching solar panels rarely works properly. I'd recommend selling that panel and controller and start from scratch. Check out these various options I've put together: https://shop.explorist.life/product-category/all-products/camper-wiring-kits/solar-charging-wiring-kits/