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Charge Controller Guide and Sizing

Ideally your charge controller amp output rating is about 25% of the total Ah of your battery bank. For example, if you’re battery bank is capable of 450Ah of current you’d like to find a charge controller which can output 112.5Ah of current. This is a bit high for most RV applications as you won’t have an array that can produce that much current. Why does this matter? If your charge controller is too small then it’s a bottle neck of the energy coming in from your charge source (solar). If your panels can produce 35 amps, but your controller can only handle 20, then you’re wasting potential charging power.

Many of the solar kits come packaged with smaller 30-35 amp charge controllers which are adequate to handle moderate current needs, but for someone with heavy current demands they aren’t up to the task. You’ll need a larger array (perhaps as high as 800 watt) and with it a larger charge controller (60-80 amp). Planning ahead is wise so if you think you’ll be expanding your system in the future it’s wise to buy accordingly.
Types and Purpose of a Charge Controller

Because the energy produced by panels has peaks and lows it it
necessary to control the power entering the batteries to ensure optimal
charging and to protect them from damage as well as maximize throughput. The
controller performs this function and can handle many panels being attached to
a single unit.

A controller does many additional functions by understanding the
charge state of your batteries and how to get the best charge with the
available current from your power source whether solar, generator or shore
power. Using complex algorithms a solar specific charge controller works
tirelessly to get every bit of power from your panels to your batteries for
optimal charging.

Single phase: Single phase chargers have
a single output and charge continuously at the same rate regardless of the
charge condition of the battery. Often they charge at a high voltage the entire
time they are connected. These are good when you need a short burst of current
(amps) to get a dead battery up to charge quickly. They don’t do well fully
topping off a battery. Once you remove the charge the battery doesn’t have time
to absorb fully the current and once it drops back down to its static internal
voltage it may be closer to 90% charged at best.

Single phase trickle: Trickle chargers also have
a single output rate but usually it’s a much lower voltage such as the mid 13
volt range and slowly bring a battery up to full voltage. These chargers are
common on rigs that often hook to shore power and simply need to keep batteries
topped off, rarely charging them from a deep discharge. A trickle charger will
do a superior job of getting a battery topped off as the lower voltage will
help the battery fully absorb the charge. The drawback is a trickle charger can
take hours to charge a dead battery fully, which isn’t ideal when you have
solar energy which comes in peaks or you need to use the generator to gives the
batteries a boost.

Multi phase: Multi phase chargers are the best of both single
phase and trickle chargers all in one with many added benefits such as complex
logic to cycle batteries and adjust output based on the current being fed into
them (solar currents vary wildly throughout the day depending on sun exposure,
clouds, shade etc). A good multiphase controller will be able to open the
current flow wide to get the batteries up to peak voltage quickly and then
switch modes to absorb to help the battery get that last tiny bit of voltage
stored and finally hold the battery at full capacity. A solar multi-phase
charger is unique because it uses more complex logic to handle the constant
varying of current coming from the solar panels and helps maximize the charging
potential for the batteries.