A PWM charge controller is rated to operate at a particular DC system voltage and maximum current. PV modules designed to work at the DC system voltage must be connected in parallel PV source circuits in order to achieve the minimum PV source size and the charge controller therefore must be sized to handle this amount of current. If the current rating of a PWM charge controller is exceeded, it can be damaged or destroyed.
Step 1: Determine PV module power rating and series configuration
The chosen DC system voltage limits the choices of modules and configurations that are possible with a PWM charge controller. Below is a table of the number of modules that can be connected in series for each PV source circuit depending upon the DC system voltage.
| DC system voltage
|
36 cell module
|
60 cell module
|
72 cell module
|
| 12 V
|
1
|
—
|
—
|
| 24 V
|
2
|
—
|
1
|
| 48 V
|
4
|
—
|
2
|
| Number of modules in series
|
=
|
Step 2: Determine proposed PV module configuration
This calculation will give a minimum number of PV modules - the result should always be rounded up. Different modules sizes and configurations can be explored to find the optimal design.
The final number of PV modules should always be larger than this value - the result should always be rounded up.
| Number of PV source circuits
|
= Minimum number of PV modules ÷ Number of modules in series (Step 1)
|
Step 3: Total PV source current
This calculation will give a minimum current rating to use as a basis for selecting the charge controller. The Isc rating of the PV module can be found on its specifications sheet. This value is multiplied by a required 1.25 safety factor to make sure the charge controller can handle periods of excessive current due to high irradiance.
| Total PV source current
|
= Final number of PV source circuits (Step 2) × Isc rating of chosen module (Step 1) × 1.25
|
Step 4: Select a charge controller
A single charge controller is the simplest and cheapest option, but for larger systems multiple charge controllers often are used in parallel. The final chosen charge controller should:
- Function at the DC system voltage.
- The charge controller(s) should have a total current rating that is larger than the minimum current rating (Step 2). Common charge controller current ratings: 4.5 A, 5 A, 6 A, 10 A, 12 A, 15 A, 20 A, 25 A, 30 A, 35 A, 40 A, 45 A, 50 A, 55 A, 60 A.
| Final charge controller current rating
|
=
|
The result of the following equation should always be rounded up.
| Number of charge controllers
|
= Total PV source current (Step 3) ÷ Final chosen charge controller current rating
|
Step 5: Determine final PV source power rating
The total power rating of the PV source can be calculated by multiplying the power rating of the chosen PV module by the final number of PV modules (Step 3).
| PV source power rating
|
= PV module power rating (Step 1) × Final number of PV modules (Step 3)
|
Notes/references
