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What Does a Solar Charge Controller Do?

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).

 


Joe

Saturday 9th of October 2021

I want to charge 2 independent battery banks from 1 solar panel. The idea is 1 battery would be the house battery and sit in our cargo trailer to run lights. The 2nd battery would be disconnected from the trailer, used elsewhere and then reconnected once it is depleted to get recharged. I have been looking at the following 3 charge controller because it looks like they are designed to handle independent battery banks. The problem is most are thinking house battery and starter battery, not my situation.

https://www.victronenergy.com/solar-charge-controllers/bluesolar-pwm-charge-controller-lcd-usb#datasheets https://www.epsolarpv.com/product/65.html https://gpelectric.com/products/30-amp-solar-controller-bluetooth/

Any advice or guidance on how you would do this?

Craig Racicot

Friday 11th of June 2021

This is huge! I have a very small trailer (17’) and room for only 2 panels. Your diagrams, calculators, and written descriptions have provided me with the understanding and knowledge to create a safe and fully functional RV solar system based on our specific needs!!! Thank you Nate!

Craig R

Scott

Sunday 6th of June 2021

Hey Nate! Many of us are finally starting to receive our Airstream Basecamp 20x trailers and I have a couple of questions that I think will help everyone out. It comes from the factory with 2x90 watt panels and a 100V 30amp MPPT controller but a lot of folks are adding 2 or 4 more 90 watt panels (for a total of 4 to 6 90 watt panels), would the 150V 35amp controller be needed for this and would it be enough?

The other big consideration, is how best to wire in an inverter. If I wire in an inverter, like say a Renogy pure sine wave inverter, is there a switch that can automatically disconnect the converter to prevent the dreaded inverter-converter charge loop? I'm assuming someone makes one but I'm not sure what it's called. If expense is no matter, do you expect there's an easy way to remove the factory converter and wire in a Victron inverter-charger all in one?

Thank you!

Nate Yarbrough

Saturday 12th of June 2021

If you wire the panels in series parallel, you could get away with the smaller 100|30 or 100|50.

Sure! Here is a 30A RV retrofit diagram that would show you how to do that: https://www.explorist.life/30a-camper-inverter-with-solar-and-alternator-charging-wiring-diagram/ The OEM converter would simply be disconnected.

Yohann

Tuesday 4th of May 2021

Hi Nate, I watched a few of your video about solar panel array and charge controller, but I am still a little bit confused, especially after looking at your calculator right there: https://www.explorist.life/solar-charge-controller-calculator/

Basically, I want to install an array of 400w solar panels. I have a Victron MPPT 100/30 and 2 Discover EVGC6A-A (in series)

My main concern is to know if the charge controller can handle 400W, even in cold temperature (I live in British Columbia).

Then secondly if I can use any the following combinations:

2x 200W "12V" solar panels in series (my original choice) 2x 200W "24V" solar panels in series (Because most 12V option are out of stock at the moment) or 4x 100W "12v" solar panels in series (least favourite option)

If those were not possible, what would recommend doing?

Thanks for all you precious content! It is so helpful :)

Carlos

Thursday 29th of April 2021

Hi Nate,

I have a question, i have 4 - 100w panels and when i use your calculator and use them in series/parallel i get 52.8 Volts and 11.44 Amp array and it recommends a viltron 100/50 Mppt. I plan on a 12 volt Lithium ion bank but i am being told that i need to run my array in just parallel and not series/parallel as that is too much volts for the controller? Can you clarify this for me?