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What Does a Solar Charge Controller Do?

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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).

 

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Brian

Sunday 28th of March 2021

VERY cool calculator Nate! Well done!

Troy Atwood

Thursday 25th of March 2021

Nate,

What software do you use to create your wiring diagrams?